44
1 Introduction of Ethernet Metcalfe’s Ethernet sketch Also refer to http://www.cs.nthu.edu.tw/~nfhuang/chap04.htm

1 Introduction of Ethernet Metcalfe’s Ethernet sketch Also refer to nfhuang/chap04.htm

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Page 1: 1 Introduction of Ethernet Metcalfe’s Ethernet sketch Also refer to nfhuang/chap04.htm

1

Introduction of Ethernet

Metcalfersquos Ethernetsketch

Also refer to httpwwwcsnthuedutw~nfhuangchap04htm

2

Questions (12)

OSI 7-layer What is LAN 如何連結電腦形成一個 LAN 是什麼網路卡 我們常用到那些網路卡 網路卡的工作是什麼 請想像 Ethernet MAC layer frame 應該要有那些欄位才能讓對方得到足夠的資訊

3

Questions (22)

同一 LAN 中的許多電腦同時透過 Ethernet 送出frames 會不會有問題

What is Multiple Access 如何用 CSMACD 的方式讓各個電腦可以在

bus 上達到相互通訊的目的 CSMACD 是好的方法嗎有沒有其他方法 如何讓 Ethernet 傳輸速度從最早 10Mbps 不斷增加再增加

Ethernet 成功的原因

4

Outlines

Ethernet History Ethernet Frame Multiple Access in Ethernet IEEE 8023

5

Part 1

Ethernet History

bus coaxial cable

switchstar

6

Ethernet History

ldquo Dominantrdquo wired LAN technology Ethernets history

Ethernets success First widely used LAN technology Simpler cheaper than token LANs and ATM Cheap $20 for NIC Kept up with speed race 10 Mbps ndash 10 Gbps

7

What is Ethernet

Link amp Physical Layers Different physical layer media fiber cable Different speeds 2 Mbps 10 Mbps 100

Mbps 1Gbps 10G bps Common MAC protocol and frame format

applicationtransportnetwork

linkphysical

MAC protocoland frame format

100BASE-TX

100BASE-T4

100BASE-FX100BASE-T2

100BASE-SX 100BASE-BX

fiber physical layercopper (twisterpair) physical layer

8

IEEE 8023 Standards

Many different Ethernet specifications Ethernet has no IEEE standard

Ethernet is similar to IEEE 8023 but not the same

9

Ethernets Name

According to PHY techniques Ethernet has several specifications and named them as

n-signal-PHY n data rate signal Base is baseband broad is broadband PHY distance media or coding methods

Examples 10Base5 10Mbs baseband 500m 10Base-T 10Mbs baseband Twisted pair

10

Comparisons of Different Spec

同軸電纜(50 )歐姆

185 m

10Mbps

925 m

30

5mm

10 Base2

每段最多可連接電腦的數目

電纜線直徑

每段最大長度

網路最大長度

資料傳輸速率

傳輸媒介

參數

同軸電纜(50 )歐姆

500 m

10Mbps

2500 m

100

10 mm

10 Base5

無遮蔽雙絞線UTP

185 m

10Mbps

500 m

-

04-06mm

10 BaseT

無遮蔽雙絞線5 UTP等級

100 m

100Mbps

-

-

-

100 BaseX

11

10Base2 Bus Topology

一條纜線的範圍稱為「區段」( segment ) 利用 MAC 位址判斷是誰的資料 若一個 T 型節點損毀則整個網路無法運作 使用終端子 ( Terminator ) 收吸收訊息的回音

A bit transmission time is 110M= 01msec

終端子

目的電腦位址MAC address03705b11345

來源電腦位址MAC address01c07b201555

12

Thin Ethernet with Repeater

3 segments connected by repeaters

terminator

repeater

Type-Tconnector

segment 1

segment 2

segment 3

兩終端電阻間最長不可超185 公尺 任兩台電腦間電

纜總長度不可超過 925 公尺

距離是05 公尺的倍數

任兩台電腦間不能超過4 個 repeater

13

10Base5 Bus Topology

terminator

repeater

Type-Tconnector

segment 1

segment 2

segment 3

兩終端電阻間最長不可超過500 公尺

任兩台電腦間電纜總長度不可超過 1500 公尺因此這 5 段同軸電纜不可以連接成一直線狀

最多 5 個 segment 任何二個工作站之間的路徑上最多只能有 2 個訊號增益器

14

10Base-T with Hub

10Base-T Centralized control by Hub

Still use Bus Topology - Broadcast Half duplex

One hub node crashes rarr Do not affect other nodes

Bus topology popular through mid 1990s All nodes in same collision domain (can

collide with each other)

HubHub

Hub

1

5

43

2 data

Hub

不可超過250 公尺

不可超過100 公尺

15

10Base-T with Switch

Centralized control by Switch Check the destination MAC address of Frame

forward this frame to a correct port No forward frames to other ports Full duplex Parallel sending many signals

Today star topology prevails Active switch in center Each ldquospokerdquo runs a (separate) Ethernet

protocol (nodes do not collide with each other)

SwitchSwitch

Switch

switchstar

16

Fast Ethernet 100BaseT Ethernet

100Mbps reduce the transmission delay of each bit

100BaseX uses 2 UTP pairs 100Base4T uses 4 UTP pairs Compatible to 10BaseT wiring system

frame format max packet size A bit transmission time is

1100M=001msec

17

Gigabit Ethernet IEEE 8023ab 1000Base-T IEEE 8023z

1000Base-SXLX Compatible to Ethernet Fast Ethernet

The same as old wiring system but speed is up to 1000Mbps

Use fiber of Category 5 UTP Used as a backbone or the

interconnection among servers

18

10 Gigabit Ethernet

IEEE 8023ae There are many differences between 8023ae

and old Ethernet specifications Use Optical Fiber Full-duplex

Have the same frame formatmax packet size Applications

Server interconnect for clusters of servers Links between switches and servers Backbone Very high-speed connections between buildings

19

Part 2

Ethernet Frame

20

Ethernet Unreliable Connectionless

Connectionless No handshaking between sending and receiving NICs NIC Network Interface Card

Unreliable receiving NIC doesnrsquot send acks or nacks to sending NIC Stream of datagrams passed to network layer

can have gaps (missing datagrams) Gaps will be filled if application is using TCP Otherwise application will see gaps

Ethernetrsquos MAC protocol unslotted CSMACD

21

Ethernet frame (13)

Define the frame in MAC layer Preamble

7 bytes with pattern 10101010 followed by one byte with pattern 10101011

Used to synchronize receiver sender clock rates

Preamble SourceDestination TypeData fromupper layer

FCS

Bytes 8 6 6 2 46-1500 4

64-1518 bytes

22

Ethernet frame (23)

Source MAC address Source accepts the data from upper layer

encapsulates as a frame then sends it to destination

Destination MAC address If adapter receives frame with matching

destination address or with broadcast address (eg ARP packet) it passes data in frame to network layer protocol Otherwise adapter discards frame

LSB=0 physical MAC address LSB=1 multicast address All 1s in 6 bytes broadcast address

23

Ethernet frame (33)

Type Indicates higher layer protocol

0800H IP 0600H XNS (Xerox protocol suit) Mostly IP but others possible eg Novell IPX

AppleTalk Data

46-1500 bytes Frame Check Sequence (FCS)

Checked at receiver If error is detected the frame is dropped

Use 32-bits CRC to check address type and data

24

Manchester Encoding

Each bit has a transition Allows clocks in sending and receiving

nodes to synchronize to each other No need for a centralized global clock among

nodes

-0225V 07V

-1825V -07V

for coaxial cable

for UTP

25

Round-trip Propagation Delay

The time delay to send a signal on one round-trip In specification the maximum distance

between 2 hosts is 2800m Use 10Mbps Ethernet as an example

Round-trip propagation delay is about 4638 s

Finally round-trip propagation delay is set to be 512 s

26

Thick Ethernet Topology

Max distance =500m3+1000m2+300m=2800m

訊號傳遞速度為光速的 065 倍 2800m2divide(3108

065)=2872s Round trip delay 還包括電纜線傳遞延遲及元件延遲等

source httpwwwcsnthuedutw~nfhuangchap04htm

27

Part 3

Multiple Access in

Ethernet

28

Sending an Ethernet Frame

Broadcast If there are two computers send data at

the same time two frames will collide A collision occurs Receivers discards these frames

CSMACD( Carrier Sense Multiple Access Collision Detection ) is used

Best Effect

29

CSMACD

Carrier Sense 表示網路卡要對 carrier 進行監測判斷網路線上是否有資料的傳送

Multiple Access 指出這種機制的目的是要讓多個網路卡可以在同一個 carrier 上存取資料

Collision Detection 表示 collision 是會發生的必須靠 detection的機制來判斷是否有 collision

30

Ethernet CSMACD algorithm (12)

1 NIC receives datagram from network layer and creates frame

2 If NIC senses channel idle starts frame transmission

If NIC senses channel busy waits until channel idle and then transmits

3 If NIC transmits entire frame without detecting another transmission NIC is done with frame

31

Ethernet CSMACD algorithm (22)

4 If NIC detects another transmission while transmitting aborts and sends jam signal Jam Signal make sure all other transmitters

are aware of collision 48 bits

5 After aborting NIC enters exponential backoff NIC chooses K at random from 012hellip2m-1

after the m th collision

NIC waits K512 bit times returns to Step 2

32

No Collision Occurs

A電腦 B電腦

A電腦 B電腦A frame開始送出

A電腦 B電腦

B聽到網路上有資 料 必須等待

A collision確定沒有繼續送資料

time=0

time=512s

Ex 10BaseT

why

33

Collision Occurs

If host B sends it frame before getting Arsquos frame a collision occurs

Host A finds noise treat it as a collision

The worst case A finds noise after a

round-trip propagation delay time

A電腦 B電腦B frame開始送出

A電腦 B電腦A frame開始送出

A電腦 B電腦collision發生

A電腦 B電腦

A collision發現接著送出

jamming signal

B collision發現

34

How Long to Find Collision

Round-trip propagation delay is 512 s for 10Mbps Ethernet

Host A must listen at least 512 s and know whether a collision occurs or not

A電腦 B電腦B frame開始送出

A電腦 B電腦A 開始送出

frame

A電腦 B電腦collision發生

A電腦 B電腦

A collision發現接著送出

Jamming signal

B collisionB發現 也 Jamming siganl會送

35

CSMACD Random Time Delay (12)

Let two collided hosts retransmit frames at a different time Host generates a random time delay (r) r 0

1 2k-1 n the number of collisions( n16) k = min (n 10)

Retransmit the frame after r Exponential backoff algorithm

The random time delay is round-trip propagation delay r For 10BaseT 512 sr

36

CSMACD Random Time Delay (22)

Goal adapt retransmission attempts to estimated current load Heavy load random wait will be

longer

37

Examples of Binary Exponential Backoff Algorithm

First collision n=1 k=min(n10)=1 r 0 1 Probability=12 to send frame immediately Probability=12 to send frame after 512 s

Second collision n=2 k=min(n10)=2 r 0 1 2 3 Four cases 0s 512 s 512times2 s 512times3

s After ten collisions choose r from

01234hellip1023

38

Data Size Limitation

To avoid that any host occupies Ethernet too long the data size is smaller than 1500 bytes

If the size of a frame is too small adapters can not detect collision in time 10MHz 01sbit Within 512s 512sdivide01sbit= 512bits

=64 bytes can be sent Every frame must be larger than 64 bytes

Data size must be larger than 46 bytes

39

Effect of CSMACD

Unpredicable when the frame can be received

Not fair Bandwidth utilization degrades if heavy

loading Not suitable for real-time applications

40

Properties of An Ethernet

Shared bus technology( broadcast) Lowest level hardware does not support

addressing Best-effort delivery mechanism No central authority to grant access Each transmission is limited in duration

41

Part 4

IEEE 8023

42

IEEE 802 Series

Fiber UTP wireless cable

80211 8023

8022 LLC (Logic Link Control)

SMTP FTPHTTP

TCP UDP

SNMP DNS

IP

Ethernet802128024 8025

bull8023 CDMACD

bull8024 Token-bus

bull8025 Token-ring

bull80211 Wireless LAN

bull80212 100VG-AnyLAN

43

IEEE 8023 Protocol

Ethernet is compatible to 8023 Length of bytes in LLC

Preamble SourceDestination Length Data from LLC FCS

Bytes 8 6 6 2 46-1500 4

64-1518 bytes

44

Flow Chart of IEEE 8023傳送訊框

組成訊框

線上有訊號

訊框過短( )衝撞

檢查碼正確

傳送訊框

發生衝撞

傳送完畢

jamming送出signal

i=i+1

i gt 16

計算延遲時間

等待延遲時間

傳送失敗傳送成功

Y es

No

No

No

Y es

Y es Y es

No

接收訊框

開始接收

接收完畢

位址辨識成功

尚有多餘位元

刪除訊框頭尾

長度錯誤對齊錯誤

Y es

No

No

No

Y es

Y es

Y es

接收成功訊框錯誤

長度欄位內容正確

No

Y es No

Y es

No

Page 2: 1 Introduction of Ethernet Metcalfe’s Ethernet sketch Also refer to nfhuang/chap04.htm

2

Questions (12)

OSI 7-layer What is LAN 如何連結電腦形成一個 LAN 是什麼網路卡 我們常用到那些網路卡 網路卡的工作是什麼 請想像 Ethernet MAC layer frame 應該要有那些欄位才能讓對方得到足夠的資訊

3

Questions (22)

同一 LAN 中的許多電腦同時透過 Ethernet 送出frames 會不會有問題

What is Multiple Access 如何用 CSMACD 的方式讓各個電腦可以在

bus 上達到相互通訊的目的 CSMACD 是好的方法嗎有沒有其他方法 如何讓 Ethernet 傳輸速度從最早 10Mbps 不斷增加再增加

Ethernet 成功的原因

4

Outlines

Ethernet History Ethernet Frame Multiple Access in Ethernet IEEE 8023

5

Part 1

Ethernet History

bus coaxial cable

switchstar

6

Ethernet History

ldquo Dominantrdquo wired LAN technology Ethernets history

Ethernets success First widely used LAN technology Simpler cheaper than token LANs and ATM Cheap $20 for NIC Kept up with speed race 10 Mbps ndash 10 Gbps

7

What is Ethernet

Link amp Physical Layers Different physical layer media fiber cable Different speeds 2 Mbps 10 Mbps 100

Mbps 1Gbps 10G bps Common MAC protocol and frame format

applicationtransportnetwork

linkphysical

MAC protocoland frame format

100BASE-TX

100BASE-T4

100BASE-FX100BASE-T2

100BASE-SX 100BASE-BX

fiber physical layercopper (twisterpair) physical layer

8

IEEE 8023 Standards

Many different Ethernet specifications Ethernet has no IEEE standard

Ethernet is similar to IEEE 8023 but not the same

9

Ethernets Name

According to PHY techniques Ethernet has several specifications and named them as

n-signal-PHY n data rate signal Base is baseband broad is broadband PHY distance media or coding methods

Examples 10Base5 10Mbs baseband 500m 10Base-T 10Mbs baseband Twisted pair

10

Comparisons of Different Spec

同軸電纜(50 )歐姆

185 m

10Mbps

925 m

30

5mm

10 Base2

每段最多可連接電腦的數目

電纜線直徑

每段最大長度

網路最大長度

資料傳輸速率

傳輸媒介

參數

同軸電纜(50 )歐姆

500 m

10Mbps

2500 m

100

10 mm

10 Base5

無遮蔽雙絞線UTP

185 m

10Mbps

500 m

-

04-06mm

10 BaseT

無遮蔽雙絞線5 UTP等級

100 m

100Mbps

-

-

-

100 BaseX

11

10Base2 Bus Topology

一條纜線的範圍稱為「區段」( segment ) 利用 MAC 位址判斷是誰的資料 若一個 T 型節點損毀則整個網路無法運作 使用終端子 ( Terminator ) 收吸收訊息的回音

A bit transmission time is 110M= 01msec

終端子

目的電腦位址MAC address03705b11345

來源電腦位址MAC address01c07b201555

12

Thin Ethernet with Repeater

3 segments connected by repeaters

terminator

repeater

Type-Tconnector

segment 1

segment 2

segment 3

兩終端電阻間最長不可超185 公尺 任兩台電腦間電

纜總長度不可超過 925 公尺

距離是05 公尺的倍數

任兩台電腦間不能超過4 個 repeater

13

10Base5 Bus Topology

terminator

repeater

Type-Tconnector

segment 1

segment 2

segment 3

兩終端電阻間最長不可超過500 公尺

任兩台電腦間電纜總長度不可超過 1500 公尺因此這 5 段同軸電纜不可以連接成一直線狀

最多 5 個 segment 任何二個工作站之間的路徑上最多只能有 2 個訊號增益器

14

10Base-T with Hub

10Base-T Centralized control by Hub

Still use Bus Topology - Broadcast Half duplex

One hub node crashes rarr Do not affect other nodes

Bus topology popular through mid 1990s All nodes in same collision domain (can

collide with each other)

HubHub

Hub

1

5

43

2 data

Hub

不可超過250 公尺

不可超過100 公尺

15

10Base-T with Switch

Centralized control by Switch Check the destination MAC address of Frame

forward this frame to a correct port No forward frames to other ports Full duplex Parallel sending many signals

Today star topology prevails Active switch in center Each ldquospokerdquo runs a (separate) Ethernet

protocol (nodes do not collide with each other)

SwitchSwitch

Switch

switchstar

16

Fast Ethernet 100BaseT Ethernet

100Mbps reduce the transmission delay of each bit

100BaseX uses 2 UTP pairs 100Base4T uses 4 UTP pairs Compatible to 10BaseT wiring system

frame format max packet size A bit transmission time is

1100M=001msec

17

Gigabit Ethernet IEEE 8023ab 1000Base-T IEEE 8023z

1000Base-SXLX Compatible to Ethernet Fast Ethernet

The same as old wiring system but speed is up to 1000Mbps

Use fiber of Category 5 UTP Used as a backbone or the

interconnection among servers

18

10 Gigabit Ethernet

IEEE 8023ae There are many differences between 8023ae

and old Ethernet specifications Use Optical Fiber Full-duplex

Have the same frame formatmax packet size Applications

Server interconnect for clusters of servers Links between switches and servers Backbone Very high-speed connections between buildings

19

Part 2

Ethernet Frame

20

Ethernet Unreliable Connectionless

Connectionless No handshaking between sending and receiving NICs NIC Network Interface Card

Unreliable receiving NIC doesnrsquot send acks or nacks to sending NIC Stream of datagrams passed to network layer

can have gaps (missing datagrams) Gaps will be filled if application is using TCP Otherwise application will see gaps

Ethernetrsquos MAC protocol unslotted CSMACD

21

Ethernet frame (13)

Define the frame in MAC layer Preamble

7 bytes with pattern 10101010 followed by one byte with pattern 10101011

Used to synchronize receiver sender clock rates

Preamble SourceDestination TypeData fromupper layer

FCS

Bytes 8 6 6 2 46-1500 4

64-1518 bytes

22

Ethernet frame (23)

Source MAC address Source accepts the data from upper layer

encapsulates as a frame then sends it to destination

Destination MAC address If adapter receives frame with matching

destination address or with broadcast address (eg ARP packet) it passes data in frame to network layer protocol Otherwise adapter discards frame

LSB=0 physical MAC address LSB=1 multicast address All 1s in 6 bytes broadcast address

23

Ethernet frame (33)

Type Indicates higher layer protocol

0800H IP 0600H XNS (Xerox protocol suit) Mostly IP but others possible eg Novell IPX

AppleTalk Data

46-1500 bytes Frame Check Sequence (FCS)

Checked at receiver If error is detected the frame is dropped

Use 32-bits CRC to check address type and data

24

Manchester Encoding

Each bit has a transition Allows clocks in sending and receiving

nodes to synchronize to each other No need for a centralized global clock among

nodes

-0225V 07V

-1825V -07V

for coaxial cable

for UTP

25

Round-trip Propagation Delay

The time delay to send a signal on one round-trip In specification the maximum distance

between 2 hosts is 2800m Use 10Mbps Ethernet as an example

Round-trip propagation delay is about 4638 s

Finally round-trip propagation delay is set to be 512 s

26

Thick Ethernet Topology

Max distance =500m3+1000m2+300m=2800m

訊號傳遞速度為光速的 065 倍 2800m2divide(3108

065)=2872s Round trip delay 還包括電纜線傳遞延遲及元件延遲等

source httpwwwcsnthuedutw~nfhuangchap04htm

27

Part 3

Multiple Access in

Ethernet

28

Sending an Ethernet Frame

Broadcast If there are two computers send data at

the same time two frames will collide A collision occurs Receivers discards these frames

CSMACD( Carrier Sense Multiple Access Collision Detection ) is used

Best Effect

29

CSMACD

Carrier Sense 表示網路卡要對 carrier 進行監測判斷網路線上是否有資料的傳送

Multiple Access 指出這種機制的目的是要讓多個網路卡可以在同一個 carrier 上存取資料

Collision Detection 表示 collision 是會發生的必須靠 detection的機制來判斷是否有 collision

30

Ethernet CSMACD algorithm (12)

1 NIC receives datagram from network layer and creates frame

2 If NIC senses channel idle starts frame transmission

If NIC senses channel busy waits until channel idle and then transmits

3 If NIC transmits entire frame without detecting another transmission NIC is done with frame

31

Ethernet CSMACD algorithm (22)

4 If NIC detects another transmission while transmitting aborts and sends jam signal Jam Signal make sure all other transmitters

are aware of collision 48 bits

5 After aborting NIC enters exponential backoff NIC chooses K at random from 012hellip2m-1

after the m th collision

NIC waits K512 bit times returns to Step 2

32

No Collision Occurs

A電腦 B電腦

A電腦 B電腦A frame開始送出

A電腦 B電腦

B聽到網路上有資 料 必須等待

A collision確定沒有繼續送資料

time=0

time=512s

Ex 10BaseT

why

33

Collision Occurs

If host B sends it frame before getting Arsquos frame a collision occurs

Host A finds noise treat it as a collision

The worst case A finds noise after a

round-trip propagation delay time

A電腦 B電腦B frame開始送出

A電腦 B電腦A frame開始送出

A電腦 B電腦collision發生

A電腦 B電腦

A collision發現接著送出

jamming signal

B collision發現

34

How Long to Find Collision

Round-trip propagation delay is 512 s for 10Mbps Ethernet

Host A must listen at least 512 s and know whether a collision occurs or not

A電腦 B電腦B frame開始送出

A電腦 B電腦A 開始送出

frame

A電腦 B電腦collision發生

A電腦 B電腦

A collision發現接著送出

Jamming signal

B collisionB發現 也 Jamming siganl會送

35

CSMACD Random Time Delay (12)

Let two collided hosts retransmit frames at a different time Host generates a random time delay (r) r 0

1 2k-1 n the number of collisions( n16) k = min (n 10)

Retransmit the frame after r Exponential backoff algorithm

The random time delay is round-trip propagation delay r For 10BaseT 512 sr

36

CSMACD Random Time Delay (22)

Goal adapt retransmission attempts to estimated current load Heavy load random wait will be

longer

37

Examples of Binary Exponential Backoff Algorithm

First collision n=1 k=min(n10)=1 r 0 1 Probability=12 to send frame immediately Probability=12 to send frame after 512 s

Second collision n=2 k=min(n10)=2 r 0 1 2 3 Four cases 0s 512 s 512times2 s 512times3

s After ten collisions choose r from

01234hellip1023

38

Data Size Limitation

To avoid that any host occupies Ethernet too long the data size is smaller than 1500 bytes

If the size of a frame is too small adapters can not detect collision in time 10MHz 01sbit Within 512s 512sdivide01sbit= 512bits

=64 bytes can be sent Every frame must be larger than 64 bytes

Data size must be larger than 46 bytes

39

Effect of CSMACD

Unpredicable when the frame can be received

Not fair Bandwidth utilization degrades if heavy

loading Not suitable for real-time applications

40

Properties of An Ethernet

Shared bus technology( broadcast) Lowest level hardware does not support

addressing Best-effort delivery mechanism No central authority to grant access Each transmission is limited in duration

41

Part 4

IEEE 8023

42

IEEE 802 Series

Fiber UTP wireless cable

80211 8023

8022 LLC (Logic Link Control)

SMTP FTPHTTP

TCP UDP

SNMP DNS

IP

Ethernet802128024 8025

bull8023 CDMACD

bull8024 Token-bus

bull8025 Token-ring

bull80211 Wireless LAN

bull80212 100VG-AnyLAN

43

IEEE 8023 Protocol

Ethernet is compatible to 8023 Length of bytes in LLC

Preamble SourceDestination Length Data from LLC FCS

Bytes 8 6 6 2 46-1500 4

64-1518 bytes

44

Flow Chart of IEEE 8023傳送訊框

組成訊框

線上有訊號

訊框過短( )衝撞

檢查碼正確

傳送訊框

發生衝撞

傳送完畢

jamming送出signal

i=i+1

i gt 16

計算延遲時間

等待延遲時間

傳送失敗傳送成功

Y es

No

No

No

Y es

Y es Y es

No

接收訊框

開始接收

接收完畢

位址辨識成功

尚有多餘位元

刪除訊框頭尾

長度錯誤對齊錯誤

Y es

No

No

No

Y es

Y es

Y es

接收成功訊框錯誤

長度欄位內容正確

No

Y es No

Y es

No

Page 3: 1 Introduction of Ethernet Metcalfe’s Ethernet sketch Also refer to nfhuang/chap04.htm

3

Questions (22)

同一 LAN 中的許多電腦同時透過 Ethernet 送出frames 會不會有問題

What is Multiple Access 如何用 CSMACD 的方式讓各個電腦可以在

bus 上達到相互通訊的目的 CSMACD 是好的方法嗎有沒有其他方法 如何讓 Ethernet 傳輸速度從最早 10Mbps 不斷增加再增加

Ethernet 成功的原因

4

Outlines

Ethernet History Ethernet Frame Multiple Access in Ethernet IEEE 8023

5

Part 1

Ethernet History

bus coaxial cable

switchstar

6

Ethernet History

ldquo Dominantrdquo wired LAN technology Ethernets history

Ethernets success First widely used LAN technology Simpler cheaper than token LANs and ATM Cheap $20 for NIC Kept up with speed race 10 Mbps ndash 10 Gbps

7

What is Ethernet

Link amp Physical Layers Different physical layer media fiber cable Different speeds 2 Mbps 10 Mbps 100

Mbps 1Gbps 10G bps Common MAC protocol and frame format

applicationtransportnetwork

linkphysical

MAC protocoland frame format

100BASE-TX

100BASE-T4

100BASE-FX100BASE-T2

100BASE-SX 100BASE-BX

fiber physical layercopper (twisterpair) physical layer

8

IEEE 8023 Standards

Many different Ethernet specifications Ethernet has no IEEE standard

Ethernet is similar to IEEE 8023 but not the same

9

Ethernets Name

According to PHY techniques Ethernet has several specifications and named them as

n-signal-PHY n data rate signal Base is baseband broad is broadband PHY distance media or coding methods

Examples 10Base5 10Mbs baseband 500m 10Base-T 10Mbs baseband Twisted pair

10

Comparisons of Different Spec

同軸電纜(50 )歐姆

185 m

10Mbps

925 m

30

5mm

10 Base2

每段最多可連接電腦的數目

電纜線直徑

每段最大長度

網路最大長度

資料傳輸速率

傳輸媒介

參數

同軸電纜(50 )歐姆

500 m

10Mbps

2500 m

100

10 mm

10 Base5

無遮蔽雙絞線UTP

185 m

10Mbps

500 m

-

04-06mm

10 BaseT

無遮蔽雙絞線5 UTP等級

100 m

100Mbps

-

-

-

100 BaseX

11

10Base2 Bus Topology

一條纜線的範圍稱為「區段」( segment ) 利用 MAC 位址判斷是誰的資料 若一個 T 型節點損毀則整個網路無法運作 使用終端子 ( Terminator ) 收吸收訊息的回音

A bit transmission time is 110M= 01msec

終端子

目的電腦位址MAC address03705b11345

來源電腦位址MAC address01c07b201555

12

Thin Ethernet with Repeater

3 segments connected by repeaters

terminator

repeater

Type-Tconnector

segment 1

segment 2

segment 3

兩終端電阻間最長不可超185 公尺 任兩台電腦間電

纜總長度不可超過 925 公尺

距離是05 公尺的倍數

任兩台電腦間不能超過4 個 repeater

13

10Base5 Bus Topology

terminator

repeater

Type-Tconnector

segment 1

segment 2

segment 3

兩終端電阻間最長不可超過500 公尺

任兩台電腦間電纜總長度不可超過 1500 公尺因此這 5 段同軸電纜不可以連接成一直線狀

最多 5 個 segment 任何二個工作站之間的路徑上最多只能有 2 個訊號增益器

14

10Base-T with Hub

10Base-T Centralized control by Hub

Still use Bus Topology - Broadcast Half duplex

One hub node crashes rarr Do not affect other nodes

Bus topology popular through mid 1990s All nodes in same collision domain (can

collide with each other)

HubHub

Hub

1

5

43

2 data

Hub

不可超過250 公尺

不可超過100 公尺

15

10Base-T with Switch

Centralized control by Switch Check the destination MAC address of Frame

forward this frame to a correct port No forward frames to other ports Full duplex Parallel sending many signals

Today star topology prevails Active switch in center Each ldquospokerdquo runs a (separate) Ethernet

protocol (nodes do not collide with each other)

SwitchSwitch

Switch

switchstar

16

Fast Ethernet 100BaseT Ethernet

100Mbps reduce the transmission delay of each bit

100BaseX uses 2 UTP pairs 100Base4T uses 4 UTP pairs Compatible to 10BaseT wiring system

frame format max packet size A bit transmission time is

1100M=001msec

17

Gigabit Ethernet IEEE 8023ab 1000Base-T IEEE 8023z

1000Base-SXLX Compatible to Ethernet Fast Ethernet

The same as old wiring system but speed is up to 1000Mbps

Use fiber of Category 5 UTP Used as a backbone or the

interconnection among servers

18

10 Gigabit Ethernet

IEEE 8023ae There are many differences between 8023ae

and old Ethernet specifications Use Optical Fiber Full-duplex

Have the same frame formatmax packet size Applications

Server interconnect for clusters of servers Links between switches and servers Backbone Very high-speed connections between buildings

19

Part 2

Ethernet Frame

20

Ethernet Unreliable Connectionless

Connectionless No handshaking between sending and receiving NICs NIC Network Interface Card

Unreliable receiving NIC doesnrsquot send acks or nacks to sending NIC Stream of datagrams passed to network layer

can have gaps (missing datagrams) Gaps will be filled if application is using TCP Otherwise application will see gaps

Ethernetrsquos MAC protocol unslotted CSMACD

21

Ethernet frame (13)

Define the frame in MAC layer Preamble

7 bytes with pattern 10101010 followed by one byte with pattern 10101011

Used to synchronize receiver sender clock rates

Preamble SourceDestination TypeData fromupper layer

FCS

Bytes 8 6 6 2 46-1500 4

64-1518 bytes

22

Ethernet frame (23)

Source MAC address Source accepts the data from upper layer

encapsulates as a frame then sends it to destination

Destination MAC address If adapter receives frame with matching

destination address or with broadcast address (eg ARP packet) it passes data in frame to network layer protocol Otherwise adapter discards frame

LSB=0 physical MAC address LSB=1 multicast address All 1s in 6 bytes broadcast address

23

Ethernet frame (33)

Type Indicates higher layer protocol

0800H IP 0600H XNS (Xerox protocol suit) Mostly IP but others possible eg Novell IPX

AppleTalk Data

46-1500 bytes Frame Check Sequence (FCS)

Checked at receiver If error is detected the frame is dropped

Use 32-bits CRC to check address type and data

24

Manchester Encoding

Each bit has a transition Allows clocks in sending and receiving

nodes to synchronize to each other No need for a centralized global clock among

nodes

-0225V 07V

-1825V -07V

for coaxial cable

for UTP

25

Round-trip Propagation Delay

The time delay to send a signal on one round-trip In specification the maximum distance

between 2 hosts is 2800m Use 10Mbps Ethernet as an example

Round-trip propagation delay is about 4638 s

Finally round-trip propagation delay is set to be 512 s

26

Thick Ethernet Topology

Max distance =500m3+1000m2+300m=2800m

訊號傳遞速度為光速的 065 倍 2800m2divide(3108

065)=2872s Round trip delay 還包括電纜線傳遞延遲及元件延遲等

source httpwwwcsnthuedutw~nfhuangchap04htm

27

Part 3

Multiple Access in

Ethernet

28

Sending an Ethernet Frame

Broadcast If there are two computers send data at

the same time two frames will collide A collision occurs Receivers discards these frames

CSMACD( Carrier Sense Multiple Access Collision Detection ) is used

Best Effect

29

CSMACD

Carrier Sense 表示網路卡要對 carrier 進行監測判斷網路線上是否有資料的傳送

Multiple Access 指出這種機制的目的是要讓多個網路卡可以在同一個 carrier 上存取資料

Collision Detection 表示 collision 是會發生的必須靠 detection的機制來判斷是否有 collision

30

Ethernet CSMACD algorithm (12)

1 NIC receives datagram from network layer and creates frame

2 If NIC senses channel idle starts frame transmission

If NIC senses channel busy waits until channel idle and then transmits

3 If NIC transmits entire frame without detecting another transmission NIC is done with frame

31

Ethernet CSMACD algorithm (22)

4 If NIC detects another transmission while transmitting aborts and sends jam signal Jam Signal make sure all other transmitters

are aware of collision 48 bits

5 After aborting NIC enters exponential backoff NIC chooses K at random from 012hellip2m-1

after the m th collision

NIC waits K512 bit times returns to Step 2

32

No Collision Occurs

A電腦 B電腦

A電腦 B電腦A frame開始送出

A電腦 B電腦

B聽到網路上有資 料 必須等待

A collision確定沒有繼續送資料

time=0

time=512s

Ex 10BaseT

why

33

Collision Occurs

If host B sends it frame before getting Arsquos frame a collision occurs

Host A finds noise treat it as a collision

The worst case A finds noise after a

round-trip propagation delay time

A電腦 B電腦B frame開始送出

A電腦 B電腦A frame開始送出

A電腦 B電腦collision發生

A電腦 B電腦

A collision發現接著送出

jamming signal

B collision發現

34

How Long to Find Collision

Round-trip propagation delay is 512 s for 10Mbps Ethernet

Host A must listen at least 512 s and know whether a collision occurs or not

A電腦 B電腦B frame開始送出

A電腦 B電腦A 開始送出

frame

A電腦 B電腦collision發生

A電腦 B電腦

A collision發現接著送出

Jamming signal

B collisionB發現 也 Jamming siganl會送

35

CSMACD Random Time Delay (12)

Let two collided hosts retransmit frames at a different time Host generates a random time delay (r) r 0

1 2k-1 n the number of collisions( n16) k = min (n 10)

Retransmit the frame after r Exponential backoff algorithm

The random time delay is round-trip propagation delay r For 10BaseT 512 sr

36

CSMACD Random Time Delay (22)

Goal adapt retransmission attempts to estimated current load Heavy load random wait will be

longer

37

Examples of Binary Exponential Backoff Algorithm

First collision n=1 k=min(n10)=1 r 0 1 Probability=12 to send frame immediately Probability=12 to send frame after 512 s

Second collision n=2 k=min(n10)=2 r 0 1 2 3 Four cases 0s 512 s 512times2 s 512times3

s After ten collisions choose r from

01234hellip1023

38

Data Size Limitation

To avoid that any host occupies Ethernet too long the data size is smaller than 1500 bytes

If the size of a frame is too small adapters can not detect collision in time 10MHz 01sbit Within 512s 512sdivide01sbit= 512bits

=64 bytes can be sent Every frame must be larger than 64 bytes

Data size must be larger than 46 bytes

39

Effect of CSMACD

Unpredicable when the frame can be received

Not fair Bandwidth utilization degrades if heavy

loading Not suitable for real-time applications

40

Properties of An Ethernet

Shared bus technology( broadcast) Lowest level hardware does not support

addressing Best-effort delivery mechanism No central authority to grant access Each transmission is limited in duration

41

Part 4

IEEE 8023

42

IEEE 802 Series

Fiber UTP wireless cable

80211 8023

8022 LLC (Logic Link Control)

SMTP FTPHTTP

TCP UDP

SNMP DNS

IP

Ethernet802128024 8025

bull8023 CDMACD

bull8024 Token-bus

bull8025 Token-ring

bull80211 Wireless LAN

bull80212 100VG-AnyLAN

43

IEEE 8023 Protocol

Ethernet is compatible to 8023 Length of bytes in LLC

Preamble SourceDestination Length Data from LLC FCS

Bytes 8 6 6 2 46-1500 4

64-1518 bytes

44

Flow Chart of IEEE 8023傳送訊框

組成訊框

線上有訊號

訊框過短( )衝撞

檢查碼正確

傳送訊框

發生衝撞

傳送完畢

jamming送出signal

i=i+1

i gt 16

計算延遲時間

等待延遲時間

傳送失敗傳送成功

Y es

No

No

No

Y es

Y es Y es

No

接收訊框

開始接收

接收完畢

位址辨識成功

尚有多餘位元

刪除訊框頭尾

長度錯誤對齊錯誤

Y es

No

No

No

Y es

Y es

Y es

接收成功訊框錯誤

長度欄位內容正確

No

Y es No

Y es

No

Page 4: 1 Introduction of Ethernet Metcalfe’s Ethernet sketch Also refer to nfhuang/chap04.htm

4

Outlines

Ethernet History Ethernet Frame Multiple Access in Ethernet IEEE 8023

5

Part 1

Ethernet History

bus coaxial cable

switchstar

6

Ethernet History

ldquo Dominantrdquo wired LAN technology Ethernets history

Ethernets success First widely used LAN technology Simpler cheaper than token LANs and ATM Cheap $20 for NIC Kept up with speed race 10 Mbps ndash 10 Gbps

7

What is Ethernet

Link amp Physical Layers Different physical layer media fiber cable Different speeds 2 Mbps 10 Mbps 100

Mbps 1Gbps 10G bps Common MAC protocol and frame format

applicationtransportnetwork

linkphysical

MAC protocoland frame format

100BASE-TX

100BASE-T4

100BASE-FX100BASE-T2

100BASE-SX 100BASE-BX

fiber physical layercopper (twisterpair) physical layer

8

IEEE 8023 Standards

Many different Ethernet specifications Ethernet has no IEEE standard

Ethernet is similar to IEEE 8023 but not the same

9

Ethernets Name

According to PHY techniques Ethernet has several specifications and named them as

n-signal-PHY n data rate signal Base is baseband broad is broadband PHY distance media or coding methods

Examples 10Base5 10Mbs baseband 500m 10Base-T 10Mbs baseband Twisted pair

10

Comparisons of Different Spec

同軸電纜(50 )歐姆

185 m

10Mbps

925 m

30

5mm

10 Base2

每段最多可連接電腦的數目

電纜線直徑

每段最大長度

網路最大長度

資料傳輸速率

傳輸媒介

參數

同軸電纜(50 )歐姆

500 m

10Mbps

2500 m

100

10 mm

10 Base5

無遮蔽雙絞線UTP

185 m

10Mbps

500 m

-

04-06mm

10 BaseT

無遮蔽雙絞線5 UTP等級

100 m

100Mbps

-

-

-

100 BaseX

11

10Base2 Bus Topology

一條纜線的範圍稱為「區段」( segment ) 利用 MAC 位址判斷是誰的資料 若一個 T 型節點損毀則整個網路無法運作 使用終端子 ( Terminator ) 收吸收訊息的回音

A bit transmission time is 110M= 01msec

終端子

目的電腦位址MAC address03705b11345

來源電腦位址MAC address01c07b201555

12

Thin Ethernet with Repeater

3 segments connected by repeaters

terminator

repeater

Type-Tconnector

segment 1

segment 2

segment 3

兩終端電阻間最長不可超185 公尺 任兩台電腦間電

纜總長度不可超過 925 公尺

距離是05 公尺的倍數

任兩台電腦間不能超過4 個 repeater

13

10Base5 Bus Topology

terminator

repeater

Type-Tconnector

segment 1

segment 2

segment 3

兩終端電阻間最長不可超過500 公尺

任兩台電腦間電纜總長度不可超過 1500 公尺因此這 5 段同軸電纜不可以連接成一直線狀

最多 5 個 segment 任何二個工作站之間的路徑上最多只能有 2 個訊號增益器

14

10Base-T with Hub

10Base-T Centralized control by Hub

Still use Bus Topology - Broadcast Half duplex

One hub node crashes rarr Do not affect other nodes

Bus topology popular through mid 1990s All nodes in same collision domain (can

collide with each other)

HubHub

Hub

1

5

43

2 data

Hub

不可超過250 公尺

不可超過100 公尺

15

10Base-T with Switch

Centralized control by Switch Check the destination MAC address of Frame

forward this frame to a correct port No forward frames to other ports Full duplex Parallel sending many signals

Today star topology prevails Active switch in center Each ldquospokerdquo runs a (separate) Ethernet

protocol (nodes do not collide with each other)

SwitchSwitch

Switch

switchstar

16

Fast Ethernet 100BaseT Ethernet

100Mbps reduce the transmission delay of each bit

100BaseX uses 2 UTP pairs 100Base4T uses 4 UTP pairs Compatible to 10BaseT wiring system

frame format max packet size A bit transmission time is

1100M=001msec

17

Gigabit Ethernet IEEE 8023ab 1000Base-T IEEE 8023z

1000Base-SXLX Compatible to Ethernet Fast Ethernet

The same as old wiring system but speed is up to 1000Mbps

Use fiber of Category 5 UTP Used as a backbone or the

interconnection among servers

18

10 Gigabit Ethernet

IEEE 8023ae There are many differences between 8023ae

and old Ethernet specifications Use Optical Fiber Full-duplex

Have the same frame formatmax packet size Applications

Server interconnect for clusters of servers Links between switches and servers Backbone Very high-speed connections between buildings

19

Part 2

Ethernet Frame

20

Ethernet Unreliable Connectionless

Connectionless No handshaking between sending and receiving NICs NIC Network Interface Card

Unreliable receiving NIC doesnrsquot send acks or nacks to sending NIC Stream of datagrams passed to network layer

can have gaps (missing datagrams) Gaps will be filled if application is using TCP Otherwise application will see gaps

Ethernetrsquos MAC protocol unslotted CSMACD

21

Ethernet frame (13)

Define the frame in MAC layer Preamble

7 bytes with pattern 10101010 followed by one byte with pattern 10101011

Used to synchronize receiver sender clock rates

Preamble SourceDestination TypeData fromupper layer

FCS

Bytes 8 6 6 2 46-1500 4

64-1518 bytes

22

Ethernet frame (23)

Source MAC address Source accepts the data from upper layer

encapsulates as a frame then sends it to destination

Destination MAC address If adapter receives frame with matching

destination address or with broadcast address (eg ARP packet) it passes data in frame to network layer protocol Otherwise adapter discards frame

LSB=0 physical MAC address LSB=1 multicast address All 1s in 6 bytes broadcast address

23

Ethernet frame (33)

Type Indicates higher layer protocol

0800H IP 0600H XNS (Xerox protocol suit) Mostly IP but others possible eg Novell IPX

AppleTalk Data

46-1500 bytes Frame Check Sequence (FCS)

Checked at receiver If error is detected the frame is dropped

Use 32-bits CRC to check address type and data

24

Manchester Encoding

Each bit has a transition Allows clocks in sending and receiving

nodes to synchronize to each other No need for a centralized global clock among

nodes

-0225V 07V

-1825V -07V

for coaxial cable

for UTP

25

Round-trip Propagation Delay

The time delay to send a signal on one round-trip In specification the maximum distance

between 2 hosts is 2800m Use 10Mbps Ethernet as an example

Round-trip propagation delay is about 4638 s

Finally round-trip propagation delay is set to be 512 s

26

Thick Ethernet Topology

Max distance =500m3+1000m2+300m=2800m

訊號傳遞速度為光速的 065 倍 2800m2divide(3108

065)=2872s Round trip delay 還包括電纜線傳遞延遲及元件延遲等

source httpwwwcsnthuedutw~nfhuangchap04htm

27

Part 3

Multiple Access in

Ethernet

28

Sending an Ethernet Frame

Broadcast If there are two computers send data at

the same time two frames will collide A collision occurs Receivers discards these frames

CSMACD( Carrier Sense Multiple Access Collision Detection ) is used

Best Effect

29

CSMACD

Carrier Sense 表示網路卡要對 carrier 進行監測判斷網路線上是否有資料的傳送

Multiple Access 指出這種機制的目的是要讓多個網路卡可以在同一個 carrier 上存取資料

Collision Detection 表示 collision 是會發生的必須靠 detection的機制來判斷是否有 collision

30

Ethernet CSMACD algorithm (12)

1 NIC receives datagram from network layer and creates frame

2 If NIC senses channel idle starts frame transmission

If NIC senses channel busy waits until channel idle and then transmits

3 If NIC transmits entire frame without detecting another transmission NIC is done with frame

31

Ethernet CSMACD algorithm (22)

4 If NIC detects another transmission while transmitting aborts and sends jam signal Jam Signal make sure all other transmitters

are aware of collision 48 bits

5 After aborting NIC enters exponential backoff NIC chooses K at random from 012hellip2m-1

after the m th collision

NIC waits K512 bit times returns to Step 2

32

No Collision Occurs

A電腦 B電腦

A電腦 B電腦A frame開始送出

A電腦 B電腦

B聽到網路上有資 料 必須等待

A collision確定沒有繼續送資料

time=0

time=512s

Ex 10BaseT

why

33

Collision Occurs

If host B sends it frame before getting Arsquos frame a collision occurs

Host A finds noise treat it as a collision

The worst case A finds noise after a

round-trip propagation delay time

A電腦 B電腦B frame開始送出

A電腦 B電腦A frame開始送出

A電腦 B電腦collision發生

A電腦 B電腦

A collision發現接著送出

jamming signal

B collision發現

34

How Long to Find Collision

Round-trip propagation delay is 512 s for 10Mbps Ethernet

Host A must listen at least 512 s and know whether a collision occurs or not

A電腦 B電腦B frame開始送出

A電腦 B電腦A 開始送出

frame

A電腦 B電腦collision發生

A電腦 B電腦

A collision發現接著送出

Jamming signal

B collisionB發現 也 Jamming siganl會送

35

CSMACD Random Time Delay (12)

Let two collided hosts retransmit frames at a different time Host generates a random time delay (r) r 0

1 2k-1 n the number of collisions( n16) k = min (n 10)

Retransmit the frame after r Exponential backoff algorithm

The random time delay is round-trip propagation delay r For 10BaseT 512 sr

36

CSMACD Random Time Delay (22)

Goal adapt retransmission attempts to estimated current load Heavy load random wait will be

longer

37

Examples of Binary Exponential Backoff Algorithm

First collision n=1 k=min(n10)=1 r 0 1 Probability=12 to send frame immediately Probability=12 to send frame after 512 s

Second collision n=2 k=min(n10)=2 r 0 1 2 3 Four cases 0s 512 s 512times2 s 512times3

s After ten collisions choose r from

01234hellip1023

38

Data Size Limitation

To avoid that any host occupies Ethernet too long the data size is smaller than 1500 bytes

If the size of a frame is too small adapters can not detect collision in time 10MHz 01sbit Within 512s 512sdivide01sbit= 512bits

=64 bytes can be sent Every frame must be larger than 64 bytes

Data size must be larger than 46 bytes

39

Effect of CSMACD

Unpredicable when the frame can be received

Not fair Bandwidth utilization degrades if heavy

loading Not suitable for real-time applications

40

Properties of An Ethernet

Shared bus technology( broadcast) Lowest level hardware does not support

addressing Best-effort delivery mechanism No central authority to grant access Each transmission is limited in duration

41

Part 4

IEEE 8023

42

IEEE 802 Series

Fiber UTP wireless cable

80211 8023

8022 LLC (Logic Link Control)

SMTP FTPHTTP

TCP UDP

SNMP DNS

IP

Ethernet802128024 8025

bull8023 CDMACD

bull8024 Token-bus

bull8025 Token-ring

bull80211 Wireless LAN

bull80212 100VG-AnyLAN

43

IEEE 8023 Protocol

Ethernet is compatible to 8023 Length of bytes in LLC

Preamble SourceDestination Length Data from LLC FCS

Bytes 8 6 6 2 46-1500 4

64-1518 bytes

44

Flow Chart of IEEE 8023傳送訊框

組成訊框

線上有訊號

訊框過短( )衝撞

檢查碼正確

傳送訊框

發生衝撞

傳送完畢

jamming送出signal

i=i+1

i gt 16

計算延遲時間

等待延遲時間

傳送失敗傳送成功

Y es

No

No

No

Y es

Y es Y es

No

接收訊框

開始接收

接收完畢

位址辨識成功

尚有多餘位元

刪除訊框頭尾

長度錯誤對齊錯誤

Y es

No

No

No

Y es

Y es

Y es

接收成功訊框錯誤

長度欄位內容正確

No

Y es No

Y es

No

Page 5: 1 Introduction of Ethernet Metcalfe’s Ethernet sketch Also refer to nfhuang/chap04.htm

5

Part 1

Ethernet History

bus coaxial cable

switchstar

6

Ethernet History

ldquo Dominantrdquo wired LAN technology Ethernets history

Ethernets success First widely used LAN technology Simpler cheaper than token LANs and ATM Cheap $20 for NIC Kept up with speed race 10 Mbps ndash 10 Gbps

7

What is Ethernet

Link amp Physical Layers Different physical layer media fiber cable Different speeds 2 Mbps 10 Mbps 100

Mbps 1Gbps 10G bps Common MAC protocol and frame format

applicationtransportnetwork

linkphysical

MAC protocoland frame format

100BASE-TX

100BASE-T4

100BASE-FX100BASE-T2

100BASE-SX 100BASE-BX

fiber physical layercopper (twisterpair) physical layer

8

IEEE 8023 Standards

Many different Ethernet specifications Ethernet has no IEEE standard

Ethernet is similar to IEEE 8023 but not the same

9

Ethernets Name

According to PHY techniques Ethernet has several specifications and named them as

n-signal-PHY n data rate signal Base is baseband broad is broadband PHY distance media or coding methods

Examples 10Base5 10Mbs baseband 500m 10Base-T 10Mbs baseband Twisted pair

10

Comparisons of Different Spec

同軸電纜(50 )歐姆

185 m

10Mbps

925 m

30

5mm

10 Base2

每段最多可連接電腦的數目

電纜線直徑

每段最大長度

網路最大長度

資料傳輸速率

傳輸媒介

參數

同軸電纜(50 )歐姆

500 m

10Mbps

2500 m

100

10 mm

10 Base5

無遮蔽雙絞線UTP

185 m

10Mbps

500 m

-

04-06mm

10 BaseT

無遮蔽雙絞線5 UTP等級

100 m

100Mbps

-

-

-

100 BaseX

11

10Base2 Bus Topology

一條纜線的範圍稱為「區段」( segment ) 利用 MAC 位址判斷是誰的資料 若一個 T 型節點損毀則整個網路無法運作 使用終端子 ( Terminator ) 收吸收訊息的回音

A bit transmission time is 110M= 01msec

終端子

目的電腦位址MAC address03705b11345

來源電腦位址MAC address01c07b201555

12

Thin Ethernet with Repeater

3 segments connected by repeaters

terminator

repeater

Type-Tconnector

segment 1

segment 2

segment 3

兩終端電阻間最長不可超185 公尺 任兩台電腦間電

纜總長度不可超過 925 公尺

距離是05 公尺的倍數

任兩台電腦間不能超過4 個 repeater

13

10Base5 Bus Topology

terminator

repeater

Type-Tconnector

segment 1

segment 2

segment 3

兩終端電阻間最長不可超過500 公尺

任兩台電腦間電纜總長度不可超過 1500 公尺因此這 5 段同軸電纜不可以連接成一直線狀

最多 5 個 segment 任何二個工作站之間的路徑上最多只能有 2 個訊號增益器

14

10Base-T with Hub

10Base-T Centralized control by Hub

Still use Bus Topology - Broadcast Half duplex

One hub node crashes rarr Do not affect other nodes

Bus topology popular through mid 1990s All nodes in same collision domain (can

collide with each other)

HubHub

Hub

1

5

43

2 data

Hub

不可超過250 公尺

不可超過100 公尺

15

10Base-T with Switch

Centralized control by Switch Check the destination MAC address of Frame

forward this frame to a correct port No forward frames to other ports Full duplex Parallel sending many signals

Today star topology prevails Active switch in center Each ldquospokerdquo runs a (separate) Ethernet

protocol (nodes do not collide with each other)

SwitchSwitch

Switch

switchstar

16

Fast Ethernet 100BaseT Ethernet

100Mbps reduce the transmission delay of each bit

100BaseX uses 2 UTP pairs 100Base4T uses 4 UTP pairs Compatible to 10BaseT wiring system

frame format max packet size A bit transmission time is

1100M=001msec

17

Gigabit Ethernet IEEE 8023ab 1000Base-T IEEE 8023z

1000Base-SXLX Compatible to Ethernet Fast Ethernet

The same as old wiring system but speed is up to 1000Mbps

Use fiber of Category 5 UTP Used as a backbone or the

interconnection among servers

18

10 Gigabit Ethernet

IEEE 8023ae There are many differences between 8023ae

and old Ethernet specifications Use Optical Fiber Full-duplex

Have the same frame formatmax packet size Applications

Server interconnect for clusters of servers Links between switches and servers Backbone Very high-speed connections between buildings

19

Part 2

Ethernet Frame

20

Ethernet Unreliable Connectionless

Connectionless No handshaking between sending and receiving NICs NIC Network Interface Card

Unreliable receiving NIC doesnrsquot send acks or nacks to sending NIC Stream of datagrams passed to network layer

can have gaps (missing datagrams) Gaps will be filled if application is using TCP Otherwise application will see gaps

Ethernetrsquos MAC protocol unslotted CSMACD

21

Ethernet frame (13)

Define the frame in MAC layer Preamble

7 bytes with pattern 10101010 followed by one byte with pattern 10101011

Used to synchronize receiver sender clock rates

Preamble SourceDestination TypeData fromupper layer

FCS

Bytes 8 6 6 2 46-1500 4

64-1518 bytes

22

Ethernet frame (23)

Source MAC address Source accepts the data from upper layer

encapsulates as a frame then sends it to destination

Destination MAC address If adapter receives frame with matching

destination address or with broadcast address (eg ARP packet) it passes data in frame to network layer protocol Otherwise adapter discards frame

LSB=0 physical MAC address LSB=1 multicast address All 1s in 6 bytes broadcast address

23

Ethernet frame (33)

Type Indicates higher layer protocol

0800H IP 0600H XNS (Xerox protocol suit) Mostly IP but others possible eg Novell IPX

AppleTalk Data

46-1500 bytes Frame Check Sequence (FCS)

Checked at receiver If error is detected the frame is dropped

Use 32-bits CRC to check address type and data

24

Manchester Encoding

Each bit has a transition Allows clocks in sending and receiving

nodes to synchronize to each other No need for a centralized global clock among

nodes

-0225V 07V

-1825V -07V

for coaxial cable

for UTP

25

Round-trip Propagation Delay

The time delay to send a signal on one round-trip In specification the maximum distance

between 2 hosts is 2800m Use 10Mbps Ethernet as an example

Round-trip propagation delay is about 4638 s

Finally round-trip propagation delay is set to be 512 s

26

Thick Ethernet Topology

Max distance =500m3+1000m2+300m=2800m

訊號傳遞速度為光速的 065 倍 2800m2divide(3108

065)=2872s Round trip delay 還包括電纜線傳遞延遲及元件延遲等

source httpwwwcsnthuedutw~nfhuangchap04htm

27

Part 3

Multiple Access in

Ethernet

28

Sending an Ethernet Frame

Broadcast If there are two computers send data at

the same time two frames will collide A collision occurs Receivers discards these frames

CSMACD( Carrier Sense Multiple Access Collision Detection ) is used

Best Effect

29

CSMACD

Carrier Sense 表示網路卡要對 carrier 進行監測判斷網路線上是否有資料的傳送

Multiple Access 指出這種機制的目的是要讓多個網路卡可以在同一個 carrier 上存取資料

Collision Detection 表示 collision 是會發生的必須靠 detection的機制來判斷是否有 collision

30

Ethernet CSMACD algorithm (12)

1 NIC receives datagram from network layer and creates frame

2 If NIC senses channel idle starts frame transmission

If NIC senses channel busy waits until channel idle and then transmits

3 If NIC transmits entire frame without detecting another transmission NIC is done with frame

31

Ethernet CSMACD algorithm (22)

4 If NIC detects another transmission while transmitting aborts and sends jam signal Jam Signal make sure all other transmitters

are aware of collision 48 bits

5 After aborting NIC enters exponential backoff NIC chooses K at random from 012hellip2m-1

after the m th collision

NIC waits K512 bit times returns to Step 2

32

No Collision Occurs

A電腦 B電腦

A電腦 B電腦A frame開始送出

A電腦 B電腦

B聽到網路上有資 料 必須等待

A collision確定沒有繼續送資料

time=0

time=512s

Ex 10BaseT

why

33

Collision Occurs

If host B sends it frame before getting Arsquos frame a collision occurs

Host A finds noise treat it as a collision

The worst case A finds noise after a

round-trip propagation delay time

A電腦 B電腦B frame開始送出

A電腦 B電腦A frame開始送出

A電腦 B電腦collision發生

A電腦 B電腦

A collision發現接著送出

jamming signal

B collision發現

34

How Long to Find Collision

Round-trip propagation delay is 512 s for 10Mbps Ethernet

Host A must listen at least 512 s and know whether a collision occurs or not

A電腦 B電腦B frame開始送出

A電腦 B電腦A 開始送出

frame

A電腦 B電腦collision發生

A電腦 B電腦

A collision發現接著送出

Jamming signal

B collisionB發現 也 Jamming siganl會送

35

CSMACD Random Time Delay (12)

Let two collided hosts retransmit frames at a different time Host generates a random time delay (r) r 0

1 2k-1 n the number of collisions( n16) k = min (n 10)

Retransmit the frame after r Exponential backoff algorithm

The random time delay is round-trip propagation delay r For 10BaseT 512 sr

36

CSMACD Random Time Delay (22)

Goal adapt retransmission attempts to estimated current load Heavy load random wait will be

longer

37

Examples of Binary Exponential Backoff Algorithm

First collision n=1 k=min(n10)=1 r 0 1 Probability=12 to send frame immediately Probability=12 to send frame after 512 s

Second collision n=2 k=min(n10)=2 r 0 1 2 3 Four cases 0s 512 s 512times2 s 512times3

s After ten collisions choose r from

01234hellip1023

38

Data Size Limitation

To avoid that any host occupies Ethernet too long the data size is smaller than 1500 bytes

If the size of a frame is too small adapters can not detect collision in time 10MHz 01sbit Within 512s 512sdivide01sbit= 512bits

=64 bytes can be sent Every frame must be larger than 64 bytes

Data size must be larger than 46 bytes

39

Effect of CSMACD

Unpredicable when the frame can be received

Not fair Bandwidth utilization degrades if heavy

loading Not suitable for real-time applications

40

Properties of An Ethernet

Shared bus technology( broadcast) Lowest level hardware does not support

addressing Best-effort delivery mechanism No central authority to grant access Each transmission is limited in duration

41

Part 4

IEEE 8023

42

IEEE 802 Series

Fiber UTP wireless cable

80211 8023

8022 LLC (Logic Link Control)

SMTP FTPHTTP

TCP UDP

SNMP DNS

IP

Ethernet802128024 8025

bull8023 CDMACD

bull8024 Token-bus

bull8025 Token-ring

bull80211 Wireless LAN

bull80212 100VG-AnyLAN

43

IEEE 8023 Protocol

Ethernet is compatible to 8023 Length of bytes in LLC

Preamble SourceDestination Length Data from LLC FCS

Bytes 8 6 6 2 46-1500 4

64-1518 bytes

44

Flow Chart of IEEE 8023傳送訊框

組成訊框

線上有訊號

訊框過短( )衝撞

檢查碼正確

傳送訊框

發生衝撞

傳送完畢

jamming送出signal

i=i+1

i gt 16

計算延遲時間

等待延遲時間

傳送失敗傳送成功

Y es

No

No

No

Y es

Y es Y es

No

接收訊框

開始接收

接收完畢

位址辨識成功

尚有多餘位元

刪除訊框頭尾

長度錯誤對齊錯誤

Y es

No

No

No

Y es

Y es

Y es

接收成功訊框錯誤

長度欄位內容正確

No

Y es No

Y es

No

Page 6: 1 Introduction of Ethernet Metcalfe’s Ethernet sketch Also refer to nfhuang/chap04.htm

6

Ethernet History

ldquo Dominantrdquo wired LAN technology Ethernets history

Ethernets success First widely used LAN technology Simpler cheaper than token LANs and ATM Cheap $20 for NIC Kept up with speed race 10 Mbps ndash 10 Gbps

7

What is Ethernet

Link amp Physical Layers Different physical layer media fiber cable Different speeds 2 Mbps 10 Mbps 100

Mbps 1Gbps 10G bps Common MAC protocol and frame format

applicationtransportnetwork

linkphysical

MAC protocoland frame format

100BASE-TX

100BASE-T4

100BASE-FX100BASE-T2

100BASE-SX 100BASE-BX

fiber physical layercopper (twisterpair) physical layer

8

IEEE 8023 Standards

Many different Ethernet specifications Ethernet has no IEEE standard

Ethernet is similar to IEEE 8023 but not the same

9

Ethernets Name

According to PHY techniques Ethernet has several specifications and named them as

n-signal-PHY n data rate signal Base is baseband broad is broadband PHY distance media or coding methods

Examples 10Base5 10Mbs baseband 500m 10Base-T 10Mbs baseband Twisted pair

10

Comparisons of Different Spec

同軸電纜(50 )歐姆

185 m

10Mbps

925 m

30

5mm

10 Base2

每段最多可連接電腦的數目

電纜線直徑

每段最大長度

網路最大長度

資料傳輸速率

傳輸媒介

參數

同軸電纜(50 )歐姆

500 m

10Mbps

2500 m

100

10 mm

10 Base5

無遮蔽雙絞線UTP

185 m

10Mbps

500 m

-

04-06mm

10 BaseT

無遮蔽雙絞線5 UTP等級

100 m

100Mbps

-

-

-

100 BaseX

11

10Base2 Bus Topology

一條纜線的範圍稱為「區段」( segment ) 利用 MAC 位址判斷是誰的資料 若一個 T 型節點損毀則整個網路無法運作 使用終端子 ( Terminator ) 收吸收訊息的回音

A bit transmission time is 110M= 01msec

終端子

目的電腦位址MAC address03705b11345

來源電腦位址MAC address01c07b201555

12

Thin Ethernet with Repeater

3 segments connected by repeaters

terminator

repeater

Type-Tconnector

segment 1

segment 2

segment 3

兩終端電阻間最長不可超185 公尺 任兩台電腦間電

纜總長度不可超過 925 公尺

距離是05 公尺的倍數

任兩台電腦間不能超過4 個 repeater

13

10Base5 Bus Topology

terminator

repeater

Type-Tconnector

segment 1

segment 2

segment 3

兩終端電阻間最長不可超過500 公尺

任兩台電腦間電纜總長度不可超過 1500 公尺因此這 5 段同軸電纜不可以連接成一直線狀

最多 5 個 segment 任何二個工作站之間的路徑上最多只能有 2 個訊號增益器

14

10Base-T with Hub

10Base-T Centralized control by Hub

Still use Bus Topology - Broadcast Half duplex

One hub node crashes rarr Do not affect other nodes

Bus topology popular through mid 1990s All nodes in same collision domain (can

collide with each other)

HubHub

Hub

1

5

43

2 data

Hub

不可超過250 公尺

不可超過100 公尺

15

10Base-T with Switch

Centralized control by Switch Check the destination MAC address of Frame

forward this frame to a correct port No forward frames to other ports Full duplex Parallel sending many signals

Today star topology prevails Active switch in center Each ldquospokerdquo runs a (separate) Ethernet

protocol (nodes do not collide with each other)

SwitchSwitch

Switch

switchstar

16

Fast Ethernet 100BaseT Ethernet

100Mbps reduce the transmission delay of each bit

100BaseX uses 2 UTP pairs 100Base4T uses 4 UTP pairs Compatible to 10BaseT wiring system

frame format max packet size A bit transmission time is

1100M=001msec

17

Gigabit Ethernet IEEE 8023ab 1000Base-T IEEE 8023z

1000Base-SXLX Compatible to Ethernet Fast Ethernet

The same as old wiring system but speed is up to 1000Mbps

Use fiber of Category 5 UTP Used as a backbone or the

interconnection among servers

18

10 Gigabit Ethernet

IEEE 8023ae There are many differences between 8023ae

and old Ethernet specifications Use Optical Fiber Full-duplex

Have the same frame formatmax packet size Applications

Server interconnect for clusters of servers Links between switches and servers Backbone Very high-speed connections between buildings

19

Part 2

Ethernet Frame

20

Ethernet Unreliable Connectionless

Connectionless No handshaking between sending and receiving NICs NIC Network Interface Card

Unreliable receiving NIC doesnrsquot send acks or nacks to sending NIC Stream of datagrams passed to network layer

can have gaps (missing datagrams) Gaps will be filled if application is using TCP Otherwise application will see gaps

Ethernetrsquos MAC protocol unslotted CSMACD

21

Ethernet frame (13)

Define the frame in MAC layer Preamble

7 bytes with pattern 10101010 followed by one byte with pattern 10101011

Used to synchronize receiver sender clock rates

Preamble SourceDestination TypeData fromupper layer

FCS

Bytes 8 6 6 2 46-1500 4

64-1518 bytes

22

Ethernet frame (23)

Source MAC address Source accepts the data from upper layer

encapsulates as a frame then sends it to destination

Destination MAC address If adapter receives frame with matching

destination address or with broadcast address (eg ARP packet) it passes data in frame to network layer protocol Otherwise adapter discards frame

LSB=0 physical MAC address LSB=1 multicast address All 1s in 6 bytes broadcast address

23

Ethernet frame (33)

Type Indicates higher layer protocol

0800H IP 0600H XNS (Xerox protocol suit) Mostly IP but others possible eg Novell IPX

AppleTalk Data

46-1500 bytes Frame Check Sequence (FCS)

Checked at receiver If error is detected the frame is dropped

Use 32-bits CRC to check address type and data

24

Manchester Encoding

Each bit has a transition Allows clocks in sending and receiving

nodes to synchronize to each other No need for a centralized global clock among

nodes

-0225V 07V

-1825V -07V

for coaxial cable

for UTP

25

Round-trip Propagation Delay

The time delay to send a signal on one round-trip In specification the maximum distance

between 2 hosts is 2800m Use 10Mbps Ethernet as an example

Round-trip propagation delay is about 4638 s

Finally round-trip propagation delay is set to be 512 s

26

Thick Ethernet Topology

Max distance =500m3+1000m2+300m=2800m

訊號傳遞速度為光速的 065 倍 2800m2divide(3108

065)=2872s Round trip delay 還包括電纜線傳遞延遲及元件延遲等

source httpwwwcsnthuedutw~nfhuangchap04htm

27

Part 3

Multiple Access in

Ethernet

28

Sending an Ethernet Frame

Broadcast If there are two computers send data at

the same time two frames will collide A collision occurs Receivers discards these frames

CSMACD( Carrier Sense Multiple Access Collision Detection ) is used

Best Effect

29

CSMACD

Carrier Sense 表示網路卡要對 carrier 進行監測判斷網路線上是否有資料的傳送

Multiple Access 指出這種機制的目的是要讓多個網路卡可以在同一個 carrier 上存取資料

Collision Detection 表示 collision 是會發生的必須靠 detection的機制來判斷是否有 collision

30

Ethernet CSMACD algorithm (12)

1 NIC receives datagram from network layer and creates frame

2 If NIC senses channel idle starts frame transmission

If NIC senses channel busy waits until channel idle and then transmits

3 If NIC transmits entire frame without detecting another transmission NIC is done with frame

31

Ethernet CSMACD algorithm (22)

4 If NIC detects another transmission while transmitting aborts and sends jam signal Jam Signal make sure all other transmitters

are aware of collision 48 bits

5 After aborting NIC enters exponential backoff NIC chooses K at random from 012hellip2m-1

after the m th collision

NIC waits K512 bit times returns to Step 2

32

No Collision Occurs

A電腦 B電腦

A電腦 B電腦A frame開始送出

A電腦 B電腦

B聽到網路上有資 料 必須等待

A collision確定沒有繼續送資料

time=0

time=512s

Ex 10BaseT

why

33

Collision Occurs

If host B sends it frame before getting Arsquos frame a collision occurs

Host A finds noise treat it as a collision

The worst case A finds noise after a

round-trip propagation delay time

A電腦 B電腦B frame開始送出

A電腦 B電腦A frame開始送出

A電腦 B電腦collision發生

A電腦 B電腦

A collision發現接著送出

jamming signal

B collision發現

34

How Long to Find Collision

Round-trip propagation delay is 512 s for 10Mbps Ethernet

Host A must listen at least 512 s and know whether a collision occurs or not

A電腦 B電腦B frame開始送出

A電腦 B電腦A 開始送出

frame

A電腦 B電腦collision發生

A電腦 B電腦

A collision發現接著送出

Jamming signal

B collisionB發現 也 Jamming siganl會送

35

CSMACD Random Time Delay (12)

Let two collided hosts retransmit frames at a different time Host generates a random time delay (r) r 0

1 2k-1 n the number of collisions( n16) k = min (n 10)

Retransmit the frame after r Exponential backoff algorithm

The random time delay is round-trip propagation delay r For 10BaseT 512 sr

36

CSMACD Random Time Delay (22)

Goal adapt retransmission attempts to estimated current load Heavy load random wait will be

longer

37

Examples of Binary Exponential Backoff Algorithm

First collision n=1 k=min(n10)=1 r 0 1 Probability=12 to send frame immediately Probability=12 to send frame after 512 s

Second collision n=2 k=min(n10)=2 r 0 1 2 3 Four cases 0s 512 s 512times2 s 512times3

s After ten collisions choose r from

01234hellip1023

38

Data Size Limitation

To avoid that any host occupies Ethernet too long the data size is smaller than 1500 bytes

If the size of a frame is too small adapters can not detect collision in time 10MHz 01sbit Within 512s 512sdivide01sbit= 512bits

=64 bytes can be sent Every frame must be larger than 64 bytes

Data size must be larger than 46 bytes

39

Effect of CSMACD

Unpredicable when the frame can be received

Not fair Bandwidth utilization degrades if heavy

loading Not suitable for real-time applications

40

Properties of An Ethernet

Shared bus technology( broadcast) Lowest level hardware does not support

addressing Best-effort delivery mechanism No central authority to grant access Each transmission is limited in duration

41

Part 4

IEEE 8023

42

IEEE 802 Series

Fiber UTP wireless cable

80211 8023

8022 LLC (Logic Link Control)

SMTP FTPHTTP

TCP UDP

SNMP DNS

IP

Ethernet802128024 8025

bull8023 CDMACD

bull8024 Token-bus

bull8025 Token-ring

bull80211 Wireless LAN

bull80212 100VG-AnyLAN

43

IEEE 8023 Protocol

Ethernet is compatible to 8023 Length of bytes in LLC

Preamble SourceDestination Length Data from LLC FCS

Bytes 8 6 6 2 46-1500 4

64-1518 bytes

44

Flow Chart of IEEE 8023傳送訊框

組成訊框

線上有訊號

訊框過短( )衝撞

檢查碼正確

傳送訊框

發生衝撞

傳送完畢

jamming送出signal

i=i+1

i gt 16

計算延遲時間

等待延遲時間

傳送失敗傳送成功

Y es

No

No

No

Y es

Y es Y es

No

接收訊框

開始接收

接收完畢

位址辨識成功

尚有多餘位元

刪除訊框頭尾

長度錯誤對齊錯誤

Y es

No

No

No

Y es

Y es

Y es

接收成功訊框錯誤

長度欄位內容正確

No

Y es No

Y es

No

Page 7: 1 Introduction of Ethernet Metcalfe’s Ethernet sketch Also refer to nfhuang/chap04.htm

7

What is Ethernet

Link amp Physical Layers Different physical layer media fiber cable Different speeds 2 Mbps 10 Mbps 100

Mbps 1Gbps 10G bps Common MAC protocol and frame format

applicationtransportnetwork

linkphysical

MAC protocoland frame format

100BASE-TX

100BASE-T4

100BASE-FX100BASE-T2

100BASE-SX 100BASE-BX

fiber physical layercopper (twisterpair) physical layer

8

IEEE 8023 Standards

Many different Ethernet specifications Ethernet has no IEEE standard

Ethernet is similar to IEEE 8023 but not the same

9

Ethernets Name

According to PHY techniques Ethernet has several specifications and named them as

n-signal-PHY n data rate signal Base is baseband broad is broadband PHY distance media or coding methods

Examples 10Base5 10Mbs baseband 500m 10Base-T 10Mbs baseband Twisted pair

10

Comparisons of Different Spec

同軸電纜(50 )歐姆

185 m

10Mbps

925 m

30

5mm

10 Base2

每段最多可連接電腦的數目

電纜線直徑

每段最大長度

網路最大長度

資料傳輸速率

傳輸媒介

參數

同軸電纜(50 )歐姆

500 m

10Mbps

2500 m

100

10 mm

10 Base5

無遮蔽雙絞線UTP

185 m

10Mbps

500 m

-

04-06mm

10 BaseT

無遮蔽雙絞線5 UTP等級

100 m

100Mbps

-

-

-

100 BaseX

11

10Base2 Bus Topology

一條纜線的範圍稱為「區段」( segment ) 利用 MAC 位址判斷是誰的資料 若一個 T 型節點損毀則整個網路無法運作 使用終端子 ( Terminator ) 收吸收訊息的回音

A bit transmission time is 110M= 01msec

終端子

目的電腦位址MAC address03705b11345

來源電腦位址MAC address01c07b201555

12

Thin Ethernet with Repeater

3 segments connected by repeaters

terminator

repeater

Type-Tconnector

segment 1

segment 2

segment 3

兩終端電阻間最長不可超185 公尺 任兩台電腦間電

纜總長度不可超過 925 公尺

距離是05 公尺的倍數

任兩台電腦間不能超過4 個 repeater

13

10Base5 Bus Topology

terminator

repeater

Type-Tconnector

segment 1

segment 2

segment 3

兩終端電阻間最長不可超過500 公尺

任兩台電腦間電纜總長度不可超過 1500 公尺因此這 5 段同軸電纜不可以連接成一直線狀

最多 5 個 segment 任何二個工作站之間的路徑上最多只能有 2 個訊號增益器

14

10Base-T with Hub

10Base-T Centralized control by Hub

Still use Bus Topology - Broadcast Half duplex

One hub node crashes rarr Do not affect other nodes

Bus topology popular through mid 1990s All nodes in same collision domain (can

collide with each other)

HubHub

Hub

1

5

43

2 data

Hub

不可超過250 公尺

不可超過100 公尺

15

10Base-T with Switch

Centralized control by Switch Check the destination MAC address of Frame

forward this frame to a correct port No forward frames to other ports Full duplex Parallel sending many signals

Today star topology prevails Active switch in center Each ldquospokerdquo runs a (separate) Ethernet

protocol (nodes do not collide with each other)

SwitchSwitch

Switch

switchstar

16

Fast Ethernet 100BaseT Ethernet

100Mbps reduce the transmission delay of each bit

100BaseX uses 2 UTP pairs 100Base4T uses 4 UTP pairs Compatible to 10BaseT wiring system

frame format max packet size A bit transmission time is

1100M=001msec

17

Gigabit Ethernet IEEE 8023ab 1000Base-T IEEE 8023z

1000Base-SXLX Compatible to Ethernet Fast Ethernet

The same as old wiring system but speed is up to 1000Mbps

Use fiber of Category 5 UTP Used as a backbone or the

interconnection among servers

18

10 Gigabit Ethernet

IEEE 8023ae There are many differences between 8023ae

and old Ethernet specifications Use Optical Fiber Full-duplex

Have the same frame formatmax packet size Applications

Server interconnect for clusters of servers Links between switches and servers Backbone Very high-speed connections between buildings

19

Part 2

Ethernet Frame

20

Ethernet Unreliable Connectionless

Connectionless No handshaking between sending and receiving NICs NIC Network Interface Card

Unreliable receiving NIC doesnrsquot send acks or nacks to sending NIC Stream of datagrams passed to network layer

can have gaps (missing datagrams) Gaps will be filled if application is using TCP Otherwise application will see gaps

Ethernetrsquos MAC protocol unslotted CSMACD

21

Ethernet frame (13)

Define the frame in MAC layer Preamble

7 bytes with pattern 10101010 followed by one byte with pattern 10101011

Used to synchronize receiver sender clock rates

Preamble SourceDestination TypeData fromupper layer

FCS

Bytes 8 6 6 2 46-1500 4

64-1518 bytes

22

Ethernet frame (23)

Source MAC address Source accepts the data from upper layer

encapsulates as a frame then sends it to destination

Destination MAC address If adapter receives frame with matching

destination address or with broadcast address (eg ARP packet) it passes data in frame to network layer protocol Otherwise adapter discards frame

LSB=0 physical MAC address LSB=1 multicast address All 1s in 6 bytes broadcast address

23

Ethernet frame (33)

Type Indicates higher layer protocol

0800H IP 0600H XNS (Xerox protocol suit) Mostly IP but others possible eg Novell IPX

AppleTalk Data

46-1500 bytes Frame Check Sequence (FCS)

Checked at receiver If error is detected the frame is dropped

Use 32-bits CRC to check address type and data

24

Manchester Encoding

Each bit has a transition Allows clocks in sending and receiving

nodes to synchronize to each other No need for a centralized global clock among

nodes

-0225V 07V

-1825V -07V

for coaxial cable

for UTP

25

Round-trip Propagation Delay

The time delay to send a signal on one round-trip In specification the maximum distance

between 2 hosts is 2800m Use 10Mbps Ethernet as an example

Round-trip propagation delay is about 4638 s

Finally round-trip propagation delay is set to be 512 s

26

Thick Ethernet Topology

Max distance =500m3+1000m2+300m=2800m

訊號傳遞速度為光速的 065 倍 2800m2divide(3108

065)=2872s Round trip delay 還包括電纜線傳遞延遲及元件延遲等

source httpwwwcsnthuedutw~nfhuangchap04htm

27

Part 3

Multiple Access in

Ethernet

28

Sending an Ethernet Frame

Broadcast If there are two computers send data at

the same time two frames will collide A collision occurs Receivers discards these frames

CSMACD( Carrier Sense Multiple Access Collision Detection ) is used

Best Effect

29

CSMACD

Carrier Sense 表示網路卡要對 carrier 進行監測判斷網路線上是否有資料的傳送

Multiple Access 指出這種機制的目的是要讓多個網路卡可以在同一個 carrier 上存取資料

Collision Detection 表示 collision 是會發生的必須靠 detection的機制來判斷是否有 collision

30

Ethernet CSMACD algorithm (12)

1 NIC receives datagram from network layer and creates frame

2 If NIC senses channel idle starts frame transmission

If NIC senses channel busy waits until channel idle and then transmits

3 If NIC transmits entire frame without detecting another transmission NIC is done with frame

31

Ethernet CSMACD algorithm (22)

4 If NIC detects another transmission while transmitting aborts and sends jam signal Jam Signal make sure all other transmitters

are aware of collision 48 bits

5 After aborting NIC enters exponential backoff NIC chooses K at random from 012hellip2m-1

after the m th collision

NIC waits K512 bit times returns to Step 2

32

No Collision Occurs

A電腦 B電腦

A電腦 B電腦A frame開始送出

A電腦 B電腦

B聽到網路上有資 料 必須等待

A collision確定沒有繼續送資料

time=0

time=512s

Ex 10BaseT

why

33

Collision Occurs

If host B sends it frame before getting Arsquos frame a collision occurs

Host A finds noise treat it as a collision

The worst case A finds noise after a

round-trip propagation delay time

A電腦 B電腦B frame開始送出

A電腦 B電腦A frame開始送出

A電腦 B電腦collision發生

A電腦 B電腦

A collision發現接著送出

jamming signal

B collision發現

34

How Long to Find Collision

Round-trip propagation delay is 512 s for 10Mbps Ethernet

Host A must listen at least 512 s and know whether a collision occurs or not

A電腦 B電腦B frame開始送出

A電腦 B電腦A 開始送出

frame

A電腦 B電腦collision發生

A電腦 B電腦

A collision發現接著送出

Jamming signal

B collisionB發現 也 Jamming siganl會送

35

CSMACD Random Time Delay (12)

Let two collided hosts retransmit frames at a different time Host generates a random time delay (r) r 0

1 2k-1 n the number of collisions( n16) k = min (n 10)

Retransmit the frame after r Exponential backoff algorithm

The random time delay is round-trip propagation delay r For 10BaseT 512 sr

36

CSMACD Random Time Delay (22)

Goal adapt retransmission attempts to estimated current load Heavy load random wait will be

longer

37

Examples of Binary Exponential Backoff Algorithm

First collision n=1 k=min(n10)=1 r 0 1 Probability=12 to send frame immediately Probability=12 to send frame after 512 s

Second collision n=2 k=min(n10)=2 r 0 1 2 3 Four cases 0s 512 s 512times2 s 512times3

s After ten collisions choose r from

01234hellip1023

38

Data Size Limitation

To avoid that any host occupies Ethernet too long the data size is smaller than 1500 bytes

If the size of a frame is too small adapters can not detect collision in time 10MHz 01sbit Within 512s 512sdivide01sbit= 512bits

=64 bytes can be sent Every frame must be larger than 64 bytes

Data size must be larger than 46 bytes

39

Effect of CSMACD

Unpredicable when the frame can be received

Not fair Bandwidth utilization degrades if heavy

loading Not suitable for real-time applications

40

Properties of An Ethernet

Shared bus technology( broadcast) Lowest level hardware does not support

addressing Best-effort delivery mechanism No central authority to grant access Each transmission is limited in duration

41

Part 4

IEEE 8023

42

IEEE 802 Series

Fiber UTP wireless cable

80211 8023

8022 LLC (Logic Link Control)

SMTP FTPHTTP

TCP UDP

SNMP DNS

IP

Ethernet802128024 8025

bull8023 CDMACD

bull8024 Token-bus

bull8025 Token-ring

bull80211 Wireless LAN

bull80212 100VG-AnyLAN

43

IEEE 8023 Protocol

Ethernet is compatible to 8023 Length of bytes in LLC

Preamble SourceDestination Length Data from LLC FCS

Bytes 8 6 6 2 46-1500 4

64-1518 bytes

44

Flow Chart of IEEE 8023傳送訊框

組成訊框

線上有訊號

訊框過短( )衝撞

檢查碼正確

傳送訊框

發生衝撞

傳送完畢

jamming送出signal

i=i+1

i gt 16

計算延遲時間

等待延遲時間

傳送失敗傳送成功

Y es

No

No

No

Y es

Y es Y es

No

接收訊框

開始接收

接收完畢

位址辨識成功

尚有多餘位元

刪除訊框頭尾

長度錯誤對齊錯誤

Y es

No

No

No

Y es

Y es

Y es

接收成功訊框錯誤

長度欄位內容正確

No

Y es No

Y es

No

Page 8: 1 Introduction of Ethernet Metcalfe’s Ethernet sketch Also refer to nfhuang/chap04.htm

8

IEEE 8023 Standards

Many different Ethernet specifications Ethernet has no IEEE standard

Ethernet is similar to IEEE 8023 but not the same

9

Ethernets Name

According to PHY techniques Ethernet has several specifications and named them as

n-signal-PHY n data rate signal Base is baseband broad is broadband PHY distance media or coding methods

Examples 10Base5 10Mbs baseband 500m 10Base-T 10Mbs baseband Twisted pair

10

Comparisons of Different Spec

同軸電纜(50 )歐姆

185 m

10Mbps

925 m

30

5mm

10 Base2

每段最多可連接電腦的數目

電纜線直徑

每段最大長度

網路最大長度

資料傳輸速率

傳輸媒介

參數

同軸電纜(50 )歐姆

500 m

10Mbps

2500 m

100

10 mm

10 Base5

無遮蔽雙絞線UTP

185 m

10Mbps

500 m

-

04-06mm

10 BaseT

無遮蔽雙絞線5 UTP等級

100 m

100Mbps

-

-

-

100 BaseX

11

10Base2 Bus Topology

一條纜線的範圍稱為「區段」( segment ) 利用 MAC 位址判斷是誰的資料 若一個 T 型節點損毀則整個網路無法運作 使用終端子 ( Terminator ) 收吸收訊息的回音

A bit transmission time is 110M= 01msec

終端子

目的電腦位址MAC address03705b11345

來源電腦位址MAC address01c07b201555

12

Thin Ethernet with Repeater

3 segments connected by repeaters

terminator

repeater

Type-Tconnector

segment 1

segment 2

segment 3

兩終端電阻間最長不可超185 公尺 任兩台電腦間電

纜總長度不可超過 925 公尺

距離是05 公尺的倍數

任兩台電腦間不能超過4 個 repeater

13

10Base5 Bus Topology

terminator

repeater

Type-Tconnector

segment 1

segment 2

segment 3

兩終端電阻間最長不可超過500 公尺

任兩台電腦間電纜總長度不可超過 1500 公尺因此這 5 段同軸電纜不可以連接成一直線狀

最多 5 個 segment 任何二個工作站之間的路徑上最多只能有 2 個訊號增益器

14

10Base-T with Hub

10Base-T Centralized control by Hub

Still use Bus Topology - Broadcast Half duplex

One hub node crashes rarr Do not affect other nodes

Bus topology popular through mid 1990s All nodes in same collision domain (can

collide with each other)

HubHub

Hub

1

5

43

2 data

Hub

不可超過250 公尺

不可超過100 公尺

15

10Base-T with Switch

Centralized control by Switch Check the destination MAC address of Frame

forward this frame to a correct port No forward frames to other ports Full duplex Parallel sending many signals

Today star topology prevails Active switch in center Each ldquospokerdquo runs a (separate) Ethernet

protocol (nodes do not collide with each other)

SwitchSwitch

Switch

switchstar

16

Fast Ethernet 100BaseT Ethernet

100Mbps reduce the transmission delay of each bit

100BaseX uses 2 UTP pairs 100Base4T uses 4 UTP pairs Compatible to 10BaseT wiring system

frame format max packet size A bit transmission time is

1100M=001msec

17

Gigabit Ethernet IEEE 8023ab 1000Base-T IEEE 8023z

1000Base-SXLX Compatible to Ethernet Fast Ethernet

The same as old wiring system but speed is up to 1000Mbps

Use fiber of Category 5 UTP Used as a backbone or the

interconnection among servers

18

10 Gigabit Ethernet

IEEE 8023ae There are many differences between 8023ae

and old Ethernet specifications Use Optical Fiber Full-duplex

Have the same frame formatmax packet size Applications

Server interconnect for clusters of servers Links between switches and servers Backbone Very high-speed connections between buildings

19

Part 2

Ethernet Frame

20

Ethernet Unreliable Connectionless

Connectionless No handshaking between sending and receiving NICs NIC Network Interface Card

Unreliable receiving NIC doesnrsquot send acks or nacks to sending NIC Stream of datagrams passed to network layer

can have gaps (missing datagrams) Gaps will be filled if application is using TCP Otherwise application will see gaps

Ethernetrsquos MAC protocol unslotted CSMACD

21

Ethernet frame (13)

Define the frame in MAC layer Preamble

7 bytes with pattern 10101010 followed by one byte with pattern 10101011

Used to synchronize receiver sender clock rates

Preamble SourceDestination TypeData fromupper layer

FCS

Bytes 8 6 6 2 46-1500 4

64-1518 bytes

22

Ethernet frame (23)

Source MAC address Source accepts the data from upper layer

encapsulates as a frame then sends it to destination

Destination MAC address If adapter receives frame with matching

destination address or with broadcast address (eg ARP packet) it passes data in frame to network layer protocol Otherwise adapter discards frame

LSB=0 physical MAC address LSB=1 multicast address All 1s in 6 bytes broadcast address

23

Ethernet frame (33)

Type Indicates higher layer protocol

0800H IP 0600H XNS (Xerox protocol suit) Mostly IP but others possible eg Novell IPX

AppleTalk Data

46-1500 bytes Frame Check Sequence (FCS)

Checked at receiver If error is detected the frame is dropped

Use 32-bits CRC to check address type and data

24

Manchester Encoding

Each bit has a transition Allows clocks in sending and receiving

nodes to synchronize to each other No need for a centralized global clock among

nodes

-0225V 07V

-1825V -07V

for coaxial cable

for UTP

25

Round-trip Propagation Delay

The time delay to send a signal on one round-trip In specification the maximum distance

between 2 hosts is 2800m Use 10Mbps Ethernet as an example

Round-trip propagation delay is about 4638 s

Finally round-trip propagation delay is set to be 512 s

26

Thick Ethernet Topology

Max distance =500m3+1000m2+300m=2800m

訊號傳遞速度為光速的 065 倍 2800m2divide(3108

065)=2872s Round trip delay 還包括電纜線傳遞延遲及元件延遲等

source httpwwwcsnthuedutw~nfhuangchap04htm

27

Part 3

Multiple Access in

Ethernet

28

Sending an Ethernet Frame

Broadcast If there are two computers send data at

the same time two frames will collide A collision occurs Receivers discards these frames

CSMACD( Carrier Sense Multiple Access Collision Detection ) is used

Best Effect

29

CSMACD

Carrier Sense 表示網路卡要對 carrier 進行監測判斷網路線上是否有資料的傳送

Multiple Access 指出這種機制的目的是要讓多個網路卡可以在同一個 carrier 上存取資料

Collision Detection 表示 collision 是會發生的必須靠 detection的機制來判斷是否有 collision

30

Ethernet CSMACD algorithm (12)

1 NIC receives datagram from network layer and creates frame

2 If NIC senses channel idle starts frame transmission

If NIC senses channel busy waits until channel idle and then transmits

3 If NIC transmits entire frame without detecting another transmission NIC is done with frame

31

Ethernet CSMACD algorithm (22)

4 If NIC detects another transmission while transmitting aborts and sends jam signal Jam Signal make sure all other transmitters

are aware of collision 48 bits

5 After aborting NIC enters exponential backoff NIC chooses K at random from 012hellip2m-1

after the m th collision

NIC waits K512 bit times returns to Step 2

32

No Collision Occurs

A電腦 B電腦

A電腦 B電腦A frame開始送出

A電腦 B電腦

B聽到網路上有資 料 必須等待

A collision確定沒有繼續送資料

time=0

time=512s

Ex 10BaseT

why

33

Collision Occurs

If host B sends it frame before getting Arsquos frame a collision occurs

Host A finds noise treat it as a collision

The worst case A finds noise after a

round-trip propagation delay time

A電腦 B電腦B frame開始送出

A電腦 B電腦A frame開始送出

A電腦 B電腦collision發生

A電腦 B電腦

A collision發現接著送出

jamming signal

B collision發現

34

How Long to Find Collision

Round-trip propagation delay is 512 s for 10Mbps Ethernet

Host A must listen at least 512 s and know whether a collision occurs or not

A電腦 B電腦B frame開始送出

A電腦 B電腦A 開始送出

frame

A電腦 B電腦collision發生

A電腦 B電腦

A collision發現接著送出

Jamming signal

B collisionB發現 也 Jamming siganl會送

35

CSMACD Random Time Delay (12)

Let two collided hosts retransmit frames at a different time Host generates a random time delay (r) r 0

1 2k-1 n the number of collisions( n16) k = min (n 10)

Retransmit the frame after r Exponential backoff algorithm

The random time delay is round-trip propagation delay r For 10BaseT 512 sr

36

CSMACD Random Time Delay (22)

Goal adapt retransmission attempts to estimated current load Heavy load random wait will be

longer

37

Examples of Binary Exponential Backoff Algorithm

First collision n=1 k=min(n10)=1 r 0 1 Probability=12 to send frame immediately Probability=12 to send frame after 512 s

Second collision n=2 k=min(n10)=2 r 0 1 2 3 Four cases 0s 512 s 512times2 s 512times3

s After ten collisions choose r from

01234hellip1023

38

Data Size Limitation

To avoid that any host occupies Ethernet too long the data size is smaller than 1500 bytes

If the size of a frame is too small adapters can not detect collision in time 10MHz 01sbit Within 512s 512sdivide01sbit= 512bits

=64 bytes can be sent Every frame must be larger than 64 bytes

Data size must be larger than 46 bytes

39

Effect of CSMACD

Unpredicable when the frame can be received

Not fair Bandwidth utilization degrades if heavy

loading Not suitable for real-time applications

40

Properties of An Ethernet

Shared bus technology( broadcast) Lowest level hardware does not support

addressing Best-effort delivery mechanism No central authority to grant access Each transmission is limited in duration

41

Part 4

IEEE 8023

42

IEEE 802 Series

Fiber UTP wireless cable

80211 8023

8022 LLC (Logic Link Control)

SMTP FTPHTTP

TCP UDP

SNMP DNS

IP

Ethernet802128024 8025

bull8023 CDMACD

bull8024 Token-bus

bull8025 Token-ring

bull80211 Wireless LAN

bull80212 100VG-AnyLAN

43

IEEE 8023 Protocol

Ethernet is compatible to 8023 Length of bytes in LLC

Preamble SourceDestination Length Data from LLC FCS

Bytes 8 6 6 2 46-1500 4

64-1518 bytes

44

Flow Chart of IEEE 8023傳送訊框

組成訊框

線上有訊號

訊框過短( )衝撞

檢查碼正確

傳送訊框

發生衝撞

傳送完畢

jamming送出signal

i=i+1

i gt 16

計算延遲時間

等待延遲時間

傳送失敗傳送成功

Y es

No

No

No

Y es

Y es Y es

No

接收訊框

開始接收

接收完畢

位址辨識成功

尚有多餘位元

刪除訊框頭尾

長度錯誤對齊錯誤

Y es

No

No

No

Y es

Y es

Y es

接收成功訊框錯誤

長度欄位內容正確

No

Y es No

Y es

No

Page 9: 1 Introduction of Ethernet Metcalfe’s Ethernet sketch Also refer to nfhuang/chap04.htm

9

Ethernets Name

According to PHY techniques Ethernet has several specifications and named them as

n-signal-PHY n data rate signal Base is baseband broad is broadband PHY distance media or coding methods

Examples 10Base5 10Mbs baseband 500m 10Base-T 10Mbs baseband Twisted pair

10

Comparisons of Different Spec

同軸電纜(50 )歐姆

185 m

10Mbps

925 m

30

5mm

10 Base2

每段最多可連接電腦的數目

電纜線直徑

每段最大長度

網路最大長度

資料傳輸速率

傳輸媒介

參數

同軸電纜(50 )歐姆

500 m

10Mbps

2500 m

100

10 mm

10 Base5

無遮蔽雙絞線UTP

185 m

10Mbps

500 m

-

04-06mm

10 BaseT

無遮蔽雙絞線5 UTP等級

100 m

100Mbps

-

-

-

100 BaseX

11

10Base2 Bus Topology

一條纜線的範圍稱為「區段」( segment ) 利用 MAC 位址判斷是誰的資料 若一個 T 型節點損毀則整個網路無法運作 使用終端子 ( Terminator ) 收吸收訊息的回音

A bit transmission time is 110M= 01msec

終端子

目的電腦位址MAC address03705b11345

來源電腦位址MAC address01c07b201555

12

Thin Ethernet with Repeater

3 segments connected by repeaters

terminator

repeater

Type-Tconnector

segment 1

segment 2

segment 3

兩終端電阻間最長不可超185 公尺 任兩台電腦間電

纜總長度不可超過 925 公尺

距離是05 公尺的倍數

任兩台電腦間不能超過4 個 repeater

13

10Base5 Bus Topology

terminator

repeater

Type-Tconnector

segment 1

segment 2

segment 3

兩終端電阻間最長不可超過500 公尺

任兩台電腦間電纜總長度不可超過 1500 公尺因此這 5 段同軸電纜不可以連接成一直線狀

最多 5 個 segment 任何二個工作站之間的路徑上最多只能有 2 個訊號增益器

14

10Base-T with Hub

10Base-T Centralized control by Hub

Still use Bus Topology - Broadcast Half duplex

One hub node crashes rarr Do not affect other nodes

Bus topology popular through mid 1990s All nodes in same collision domain (can

collide with each other)

HubHub

Hub

1

5

43

2 data

Hub

不可超過250 公尺

不可超過100 公尺

15

10Base-T with Switch

Centralized control by Switch Check the destination MAC address of Frame

forward this frame to a correct port No forward frames to other ports Full duplex Parallel sending many signals

Today star topology prevails Active switch in center Each ldquospokerdquo runs a (separate) Ethernet

protocol (nodes do not collide with each other)

SwitchSwitch

Switch

switchstar

16

Fast Ethernet 100BaseT Ethernet

100Mbps reduce the transmission delay of each bit

100BaseX uses 2 UTP pairs 100Base4T uses 4 UTP pairs Compatible to 10BaseT wiring system

frame format max packet size A bit transmission time is

1100M=001msec

17

Gigabit Ethernet IEEE 8023ab 1000Base-T IEEE 8023z

1000Base-SXLX Compatible to Ethernet Fast Ethernet

The same as old wiring system but speed is up to 1000Mbps

Use fiber of Category 5 UTP Used as a backbone or the

interconnection among servers

18

10 Gigabit Ethernet

IEEE 8023ae There are many differences between 8023ae

and old Ethernet specifications Use Optical Fiber Full-duplex

Have the same frame formatmax packet size Applications

Server interconnect for clusters of servers Links between switches and servers Backbone Very high-speed connections between buildings

19

Part 2

Ethernet Frame

20

Ethernet Unreliable Connectionless

Connectionless No handshaking between sending and receiving NICs NIC Network Interface Card

Unreliable receiving NIC doesnrsquot send acks or nacks to sending NIC Stream of datagrams passed to network layer

can have gaps (missing datagrams) Gaps will be filled if application is using TCP Otherwise application will see gaps

Ethernetrsquos MAC protocol unslotted CSMACD

21

Ethernet frame (13)

Define the frame in MAC layer Preamble

7 bytes with pattern 10101010 followed by one byte with pattern 10101011

Used to synchronize receiver sender clock rates

Preamble SourceDestination TypeData fromupper layer

FCS

Bytes 8 6 6 2 46-1500 4

64-1518 bytes

22

Ethernet frame (23)

Source MAC address Source accepts the data from upper layer

encapsulates as a frame then sends it to destination

Destination MAC address If adapter receives frame with matching

destination address or with broadcast address (eg ARP packet) it passes data in frame to network layer protocol Otherwise adapter discards frame

LSB=0 physical MAC address LSB=1 multicast address All 1s in 6 bytes broadcast address

23

Ethernet frame (33)

Type Indicates higher layer protocol

0800H IP 0600H XNS (Xerox protocol suit) Mostly IP but others possible eg Novell IPX

AppleTalk Data

46-1500 bytes Frame Check Sequence (FCS)

Checked at receiver If error is detected the frame is dropped

Use 32-bits CRC to check address type and data

24

Manchester Encoding

Each bit has a transition Allows clocks in sending and receiving

nodes to synchronize to each other No need for a centralized global clock among

nodes

-0225V 07V

-1825V -07V

for coaxial cable

for UTP

25

Round-trip Propagation Delay

The time delay to send a signal on one round-trip In specification the maximum distance

between 2 hosts is 2800m Use 10Mbps Ethernet as an example

Round-trip propagation delay is about 4638 s

Finally round-trip propagation delay is set to be 512 s

26

Thick Ethernet Topology

Max distance =500m3+1000m2+300m=2800m

訊號傳遞速度為光速的 065 倍 2800m2divide(3108

065)=2872s Round trip delay 還包括電纜線傳遞延遲及元件延遲等

source httpwwwcsnthuedutw~nfhuangchap04htm

27

Part 3

Multiple Access in

Ethernet

28

Sending an Ethernet Frame

Broadcast If there are two computers send data at

the same time two frames will collide A collision occurs Receivers discards these frames

CSMACD( Carrier Sense Multiple Access Collision Detection ) is used

Best Effect

29

CSMACD

Carrier Sense 表示網路卡要對 carrier 進行監測判斷網路線上是否有資料的傳送

Multiple Access 指出這種機制的目的是要讓多個網路卡可以在同一個 carrier 上存取資料

Collision Detection 表示 collision 是會發生的必須靠 detection的機制來判斷是否有 collision

30

Ethernet CSMACD algorithm (12)

1 NIC receives datagram from network layer and creates frame

2 If NIC senses channel idle starts frame transmission

If NIC senses channel busy waits until channel idle and then transmits

3 If NIC transmits entire frame without detecting another transmission NIC is done with frame

31

Ethernet CSMACD algorithm (22)

4 If NIC detects another transmission while transmitting aborts and sends jam signal Jam Signal make sure all other transmitters

are aware of collision 48 bits

5 After aborting NIC enters exponential backoff NIC chooses K at random from 012hellip2m-1

after the m th collision

NIC waits K512 bit times returns to Step 2

32

No Collision Occurs

A電腦 B電腦

A電腦 B電腦A frame開始送出

A電腦 B電腦

B聽到網路上有資 料 必須等待

A collision確定沒有繼續送資料

time=0

time=512s

Ex 10BaseT

why

33

Collision Occurs

If host B sends it frame before getting Arsquos frame a collision occurs

Host A finds noise treat it as a collision

The worst case A finds noise after a

round-trip propagation delay time

A電腦 B電腦B frame開始送出

A電腦 B電腦A frame開始送出

A電腦 B電腦collision發生

A電腦 B電腦

A collision發現接著送出

jamming signal

B collision發現

34

How Long to Find Collision

Round-trip propagation delay is 512 s for 10Mbps Ethernet

Host A must listen at least 512 s and know whether a collision occurs or not

A電腦 B電腦B frame開始送出

A電腦 B電腦A 開始送出

frame

A電腦 B電腦collision發生

A電腦 B電腦

A collision發現接著送出

Jamming signal

B collisionB發現 也 Jamming siganl會送

35

CSMACD Random Time Delay (12)

Let two collided hosts retransmit frames at a different time Host generates a random time delay (r) r 0

1 2k-1 n the number of collisions( n16) k = min (n 10)

Retransmit the frame after r Exponential backoff algorithm

The random time delay is round-trip propagation delay r For 10BaseT 512 sr

36

CSMACD Random Time Delay (22)

Goal adapt retransmission attempts to estimated current load Heavy load random wait will be

longer

37

Examples of Binary Exponential Backoff Algorithm

First collision n=1 k=min(n10)=1 r 0 1 Probability=12 to send frame immediately Probability=12 to send frame after 512 s

Second collision n=2 k=min(n10)=2 r 0 1 2 3 Four cases 0s 512 s 512times2 s 512times3

s After ten collisions choose r from

01234hellip1023

38

Data Size Limitation

To avoid that any host occupies Ethernet too long the data size is smaller than 1500 bytes

If the size of a frame is too small adapters can not detect collision in time 10MHz 01sbit Within 512s 512sdivide01sbit= 512bits

=64 bytes can be sent Every frame must be larger than 64 bytes

Data size must be larger than 46 bytes

39

Effect of CSMACD

Unpredicable when the frame can be received

Not fair Bandwidth utilization degrades if heavy

loading Not suitable for real-time applications

40

Properties of An Ethernet

Shared bus technology( broadcast) Lowest level hardware does not support

addressing Best-effort delivery mechanism No central authority to grant access Each transmission is limited in duration

41

Part 4

IEEE 8023

42

IEEE 802 Series

Fiber UTP wireless cable

80211 8023

8022 LLC (Logic Link Control)

SMTP FTPHTTP

TCP UDP

SNMP DNS

IP

Ethernet802128024 8025

bull8023 CDMACD

bull8024 Token-bus

bull8025 Token-ring

bull80211 Wireless LAN

bull80212 100VG-AnyLAN

43

IEEE 8023 Protocol

Ethernet is compatible to 8023 Length of bytes in LLC

Preamble SourceDestination Length Data from LLC FCS

Bytes 8 6 6 2 46-1500 4

64-1518 bytes

44

Flow Chart of IEEE 8023傳送訊框

組成訊框

線上有訊號

訊框過短( )衝撞

檢查碼正確

傳送訊框

發生衝撞

傳送完畢

jamming送出signal

i=i+1

i gt 16

計算延遲時間

等待延遲時間

傳送失敗傳送成功

Y es

No

No

No

Y es

Y es Y es

No

接收訊框

開始接收

接收完畢

位址辨識成功

尚有多餘位元

刪除訊框頭尾

長度錯誤對齊錯誤

Y es

No

No

No

Y es

Y es

Y es

接收成功訊框錯誤

長度欄位內容正確

No

Y es No

Y es

No

Page 10: 1 Introduction of Ethernet Metcalfe’s Ethernet sketch Also refer to nfhuang/chap04.htm

10

Comparisons of Different Spec

同軸電纜(50 )歐姆

185 m

10Mbps

925 m

30

5mm

10 Base2

每段最多可連接電腦的數目

電纜線直徑

每段最大長度

網路最大長度

資料傳輸速率

傳輸媒介

參數

同軸電纜(50 )歐姆

500 m

10Mbps

2500 m

100

10 mm

10 Base5

無遮蔽雙絞線UTP

185 m

10Mbps

500 m

-

04-06mm

10 BaseT

無遮蔽雙絞線5 UTP等級

100 m

100Mbps

-

-

-

100 BaseX

11

10Base2 Bus Topology

一條纜線的範圍稱為「區段」( segment ) 利用 MAC 位址判斷是誰的資料 若一個 T 型節點損毀則整個網路無法運作 使用終端子 ( Terminator ) 收吸收訊息的回音

A bit transmission time is 110M= 01msec

終端子

目的電腦位址MAC address03705b11345

來源電腦位址MAC address01c07b201555

12

Thin Ethernet with Repeater

3 segments connected by repeaters

terminator

repeater

Type-Tconnector

segment 1

segment 2

segment 3

兩終端電阻間最長不可超185 公尺 任兩台電腦間電

纜總長度不可超過 925 公尺

距離是05 公尺的倍數

任兩台電腦間不能超過4 個 repeater

13

10Base5 Bus Topology

terminator

repeater

Type-Tconnector

segment 1

segment 2

segment 3

兩終端電阻間最長不可超過500 公尺

任兩台電腦間電纜總長度不可超過 1500 公尺因此這 5 段同軸電纜不可以連接成一直線狀

最多 5 個 segment 任何二個工作站之間的路徑上最多只能有 2 個訊號增益器

14

10Base-T with Hub

10Base-T Centralized control by Hub

Still use Bus Topology - Broadcast Half duplex

One hub node crashes rarr Do not affect other nodes

Bus topology popular through mid 1990s All nodes in same collision domain (can

collide with each other)

HubHub

Hub

1

5

43

2 data

Hub

不可超過250 公尺

不可超過100 公尺

15

10Base-T with Switch

Centralized control by Switch Check the destination MAC address of Frame

forward this frame to a correct port No forward frames to other ports Full duplex Parallel sending many signals

Today star topology prevails Active switch in center Each ldquospokerdquo runs a (separate) Ethernet

protocol (nodes do not collide with each other)

SwitchSwitch

Switch

switchstar

16

Fast Ethernet 100BaseT Ethernet

100Mbps reduce the transmission delay of each bit

100BaseX uses 2 UTP pairs 100Base4T uses 4 UTP pairs Compatible to 10BaseT wiring system

frame format max packet size A bit transmission time is

1100M=001msec

17

Gigabit Ethernet IEEE 8023ab 1000Base-T IEEE 8023z

1000Base-SXLX Compatible to Ethernet Fast Ethernet

The same as old wiring system but speed is up to 1000Mbps

Use fiber of Category 5 UTP Used as a backbone or the

interconnection among servers

18

10 Gigabit Ethernet

IEEE 8023ae There are many differences between 8023ae

and old Ethernet specifications Use Optical Fiber Full-duplex

Have the same frame formatmax packet size Applications

Server interconnect for clusters of servers Links between switches and servers Backbone Very high-speed connections between buildings

19

Part 2

Ethernet Frame

20

Ethernet Unreliable Connectionless

Connectionless No handshaking between sending and receiving NICs NIC Network Interface Card

Unreliable receiving NIC doesnrsquot send acks or nacks to sending NIC Stream of datagrams passed to network layer

can have gaps (missing datagrams) Gaps will be filled if application is using TCP Otherwise application will see gaps

Ethernetrsquos MAC protocol unslotted CSMACD

21

Ethernet frame (13)

Define the frame in MAC layer Preamble

7 bytes with pattern 10101010 followed by one byte with pattern 10101011

Used to synchronize receiver sender clock rates

Preamble SourceDestination TypeData fromupper layer

FCS

Bytes 8 6 6 2 46-1500 4

64-1518 bytes

22

Ethernet frame (23)

Source MAC address Source accepts the data from upper layer

encapsulates as a frame then sends it to destination

Destination MAC address If adapter receives frame with matching

destination address or with broadcast address (eg ARP packet) it passes data in frame to network layer protocol Otherwise adapter discards frame

LSB=0 physical MAC address LSB=1 multicast address All 1s in 6 bytes broadcast address

23

Ethernet frame (33)

Type Indicates higher layer protocol

0800H IP 0600H XNS (Xerox protocol suit) Mostly IP but others possible eg Novell IPX

AppleTalk Data

46-1500 bytes Frame Check Sequence (FCS)

Checked at receiver If error is detected the frame is dropped

Use 32-bits CRC to check address type and data

24

Manchester Encoding

Each bit has a transition Allows clocks in sending and receiving

nodes to synchronize to each other No need for a centralized global clock among

nodes

-0225V 07V

-1825V -07V

for coaxial cable

for UTP

25

Round-trip Propagation Delay

The time delay to send a signal on one round-trip In specification the maximum distance

between 2 hosts is 2800m Use 10Mbps Ethernet as an example

Round-trip propagation delay is about 4638 s

Finally round-trip propagation delay is set to be 512 s

26

Thick Ethernet Topology

Max distance =500m3+1000m2+300m=2800m

訊號傳遞速度為光速的 065 倍 2800m2divide(3108

065)=2872s Round trip delay 還包括電纜線傳遞延遲及元件延遲等

source httpwwwcsnthuedutw~nfhuangchap04htm

27

Part 3

Multiple Access in

Ethernet

28

Sending an Ethernet Frame

Broadcast If there are two computers send data at

the same time two frames will collide A collision occurs Receivers discards these frames

CSMACD( Carrier Sense Multiple Access Collision Detection ) is used

Best Effect

29

CSMACD

Carrier Sense 表示網路卡要對 carrier 進行監測判斷網路線上是否有資料的傳送

Multiple Access 指出這種機制的目的是要讓多個網路卡可以在同一個 carrier 上存取資料

Collision Detection 表示 collision 是會發生的必須靠 detection的機制來判斷是否有 collision

30

Ethernet CSMACD algorithm (12)

1 NIC receives datagram from network layer and creates frame

2 If NIC senses channel idle starts frame transmission

If NIC senses channel busy waits until channel idle and then transmits

3 If NIC transmits entire frame without detecting another transmission NIC is done with frame

31

Ethernet CSMACD algorithm (22)

4 If NIC detects another transmission while transmitting aborts and sends jam signal Jam Signal make sure all other transmitters

are aware of collision 48 bits

5 After aborting NIC enters exponential backoff NIC chooses K at random from 012hellip2m-1

after the m th collision

NIC waits K512 bit times returns to Step 2

32

No Collision Occurs

A電腦 B電腦

A電腦 B電腦A frame開始送出

A電腦 B電腦

B聽到網路上有資 料 必須等待

A collision確定沒有繼續送資料

time=0

time=512s

Ex 10BaseT

why

33

Collision Occurs

If host B sends it frame before getting Arsquos frame a collision occurs

Host A finds noise treat it as a collision

The worst case A finds noise after a

round-trip propagation delay time

A電腦 B電腦B frame開始送出

A電腦 B電腦A frame開始送出

A電腦 B電腦collision發生

A電腦 B電腦

A collision發現接著送出

jamming signal

B collision發現

34

How Long to Find Collision

Round-trip propagation delay is 512 s for 10Mbps Ethernet

Host A must listen at least 512 s and know whether a collision occurs or not

A電腦 B電腦B frame開始送出

A電腦 B電腦A 開始送出

frame

A電腦 B電腦collision發生

A電腦 B電腦

A collision發現接著送出

Jamming signal

B collisionB發現 也 Jamming siganl會送

35

CSMACD Random Time Delay (12)

Let two collided hosts retransmit frames at a different time Host generates a random time delay (r) r 0

1 2k-1 n the number of collisions( n16) k = min (n 10)

Retransmit the frame after r Exponential backoff algorithm

The random time delay is round-trip propagation delay r For 10BaseT 512 sr

36

CSMACD Random Time Delay (22)

Goal adapt retransmission attempts to estimated current load Heavy load random wait will be

longer

37

Examples of Binary Exponential Backoff Algorithm

First collision n=1 k=min(n10)=1 r 0 1 Probability=12 to send frame immediately Probability=12 to send frame after 512 s

Second collision n=2 k=min(n10)=2 r 0 1 2 3 Four cases 0s 512 s 512times2 s 512times3

s After ten collisions choose r from

01234hellip1023

38

Data Size Limitation

To avoid that any host occupies Ethernet too long the data size is smaller than 1500 bytes

If the size of a frame is too small adapters can not detect collision in time 10MHz 01sbit Within 512s 512sdivide01sbit= 512bits

=64 bytes can be sent Every frame must be larger than 64 bytes

Data size must be larger than 46 bytes

39

Effect of CSMACD

Unpredicable when the frame can be received

Not fair Bandwidth utilization degrades if heavy

loading Not suitable for real-time applications

40

Properties of An Ethernet

Shared bus technology( broadcast) Lowest level hardware does not support

addressing Best-effort delivery mechanism No central authority to grant access Each transmission is limited in duration

41

Part 4

IEEE 8023

42

IEEE 802 Series

Fiber UTP wireless cable

80211 8023

8022 LLC (Logic Link Control)

SMTP FTPHTTP

TCP UDP

SNMP DNS

IP

Ethernet802128024 8025

bull8023 CDMACD

bull8024 Token-bus

bull8025 Token-ring

bull80211 Wireless LAN

bull80212 100VG-AnyLAN

43

IEEE 8023 Protocol

Ethernet is compatible to 8023 Length of bytes in LLC

Preamble SourceDestination Length Data from LLC FCS

Bytes 8 6 6 2 46-1500 4

64-1518 bytes

44

Flow Chart of IEEE 8023傳送訊框

組成訊框

線上有訊號

訊框過短( )衝撞

檢查碼正確

傳送訊框

發生衝撞

傳送完畢

jamming送出signal

i=i+1

i gt 16

計算延遲時間

等待延遲時間

傳送失敗傳送成功

Y es

No

No

No

Y es

Y es Y es

No

接收訊框

開始接收

接收完畢

位址辨識成功

尚有多餘位元

刪除訊框頭尾

長度錯誤對齊錯誤

Y es

No

No

No

Y es

Y es

Y es

接收成功訊框錯誤

長度欄位內容正確

No

Y es No

Y es

No

Page 11: 1 Introduction of Ethernet Metcalfe’s Ethernet sketch Also refer to nfhuang/chap04.htm

11

10Base2 Bus Topology

一條纜線的範圍稱為「區段」( segment ) 利用 MAC 位址判斷是誰的資料 若一個 T 型節點損毀則整個網路無法運作 使用終端子 ( Terminator ) 收吸收訊息的回音

A bit transmission time is 110M= 01msec

終端子

目的電腦位址MAC address03705b11345

來源電腦位址MAC address01c07b201555

12

Thin Ethernet with Repeater

3 segments connected by repeaters

terminator

repeater

Type-Tconnector

segment 1

segment 2

segment 3

兩終端電阻間最長不可超185 公尺 任兩台電腦間電

纜總長度不可超過 925 公尺

距離是05 公尺的倍數

任兩台電腦間不能超過4 個 repeater

13

10Base5 Bus Topology

terminator

repeater

Type-Tconnector

segment 1

segment 2

segment 3

兩終端電阻間最長不可超過500 公尺

任兩台電腦間電纜總長度不可超過 1500 公尺因此這 5 段同軸電纜不可以連接成一直線狀

最多 5 個 segment 任何二個工作站之間的路徑上最多只能有 2 個訊號增益器

14

10Base-T with Hub

10Base-T Centralized control by Hub

Still use Bus Topology - Broadcast Half duplex

One hub node crashes rarr Do not affect other nodes

Bus topology popular through mid 1990s All nodes in same collision domain (can

collide with each other)

HubHub

Hub

1

5

43

2 data

Hub

不可超過250 公尺

不可超過100 公尺

15

10Base-T with Switch

Centralized control by Switch Check the destination MAC address of Frame

forward this frame to a correct port No forward frames to other ports Full duplex Parallel sending many signals

Today star topology prevails Active switch in center Each ldquospokerdquo runs a (separate) Ethernet

protocol (nodes do not collide with each other)

SwitchSwitch

Switch

switchstar

16

Fast Ethernet 100BaseT Ethernet

100Mbps reduce the transmission delay of each bit

100BaseX uses 2 UTP pairs 100Base4T uses 4 UTP pairs Compatible to 10BaseT wiring system

frame format max packet size A bit transmission time is

1100M=001msec

17

Gigabit Ethernet IEEE 8023ab 1000Base-T IEEE 8023z

1000Base-SXLX Compatible to Ethernet Fast Ethernet

The same as old wiring system but speed is up to 1000Mbps

Use fiber of Category 5 UTP Used as a backbone or the

interconnection among servers

18

10 Gigabit Ethernet

IEEE 8023ae There are many differences between 8023ae

and old Ethernet specifications Use Optical Fiber Full-duplex

Have the same frame formatmax packet size Applications

Server interconnect for clusters of servers Links between switches and servers Backbone Very high-speed connections between buildings

19

Part 2

Ethernet Frame

20

Ethernet Unreliable Connectionless

Connectionless No handshaking between sending and receiving NICs NIC Network Interface Card

Unreliable receiving NIC doesnrsquot send acks or nacks to sending NIC Stream of datagrams passed to network layer

can have gaps (missing datagrams) Gaps will be filled if application is using TCP Otherwise application will see gaps

Ethernetrsquos MAC protocol unslotted CSMACD

21

Ethernet frame (13)

Define the frame in MAC layer Preamble

7 bytes with pattern 10101010 followed by one byte with pattern 10101011

Used to synchronize receiver sender clock rates

Preamble SourceDestination TypeData fromupper layer

FCS

Bytes 8 6 6 2 46-1500 4

64-1518 bytes

22

Ethernet frame (23)

Source MAC address Source accepts the data from upper layer

encapsulates as a frame then sends it to destination

Destination MAC address If adapter receives frame with matching

destination address or with broadcast address (eg ARP packet) it passes data in frame to network layer protocol Otherwise adapter discards frame

LSB=0 physical MAC address LSB=1 multicast address All 1s in 6 bytes broadcast address

23

Ethernet frame (33)

Type Indicates higher layer protocol

0800H IP 0600H XNS (Xerox protocol suit) Mostly IP but others possible eg Novell IPX

AppleTalk Data

46-1500 bytes Frame Check Sequence (FCS)

Checked at receiver If error is detected the frame is dropped

Use 32-bits CRC to check address type and data

24

Manchester Encoding

Each bit has a transition Allows clocks in sending and receiving

nodes to synchronize to each other No need for a centralized global clock among

nodes

-0225V 07V

-1825V -07V

for coaxial cable

for UTP

25

Round-trip Propagation Delay

The time delay to send a signal on one round-trip In specification the maximum distance

between 2 hosts is 2800m Use 10Mbps Ethernet as an example

Round-trip propagation delay is about 4638 s

Finally round-trip propagation delay is set to be 512 s

26

Thick Ethernet Topology

Max distance =500m3+1000m2+300m=2800m

訊號傳遞速度為光速的 065 倍 2800m2divide(3108

065)=2872s Round trip delay 還包括電纜線傳遞延遲及元件延遲等

source httpwwwcsnthuedutw~nfhuangchap04htm

27

Part 3

Multiple Access in

Ethernet

28

Sending an Ethernet Frame

Broadcast If there are two computers send data at

the same time two frames will collide A collision occurs Receivers discards these frames

CSMACD( Carrier Sense Multiple Access Collision Detection ) is used

Best Effect

29

CSMACD

Carrier Sense 表示網路卡要對 carrier 進行監測判斷網路線上是否有資料的傳送

Multiple Access 指出這種機制的目的是要讓多個網路卡可以在同一個 carrier 上存取資料

Collision Detection 表示 collision 是會發生的必須靠 detection的機制來判斷是否有 collision

30

Ethernet CSMACD algorithm (12)

1 NIC receives datagram from network layer and creates frame

2 If NIC senses channel idle starts frame transmission

If NIC senses channel busy waits until channel idle and then transmits

3 If NIC transmits entire frame without detecting another transmission NIC is done with frame

31

Ethernet CSMACD algorithm (22)

4 If NIC detects another transmission while transmitting aborts and sends jam signal Jam Signal make sure all other transmitters

are aware of collision 48 bits

5 After aborting NIC enters exponential backoff NIC chooses K at random from 012hellip2m-1

after the m th collision

NIC waits K512 bit times returns to Step 2

32

No Collision Occurs

A電腦 B電腦

A電腦 B電腦A frame開始送出

A電腦 B電腦

B聽到網路上有資 料 必須等待

A collision確定沒有繼續送資料

time=0

time=512s

Ex 10BaseT

why

33

Collision Occurs

If host B sends it frame before getting Arsquos frame a collision occurs

Host A finds noise treat it as a collision

The worst case A finds noise after a

round-trip propagation delay time

A電腦 B電腦B frame開始送出

A電腦 B電腦A frame開始送出

A電腦 B電腦collision發生

A電腦 B電腦

A collision發現接著送出

jamming signal

B collision發現

34

How Long to Find Collision

Round-trip propagation delay is 512 s for 10Mbps Ethernet

Host A must listen at least 512 s and know whether a collision occurs or not

A電腦 B電腦B frame開始送出

A電腦 B電腦A 開始送出

frame

A電腦 B電腦collision發生

A電腦 B電腦

A collision發現接著送出

Jamming signal

B collisionB發現 也 Jamming siganl會送

35

CSMACD Random Time Delay (12)

Let two collided hosts retransmit frames at a different time Host generates a random time delay (r) r 0

1 2k-1 n the number of collisions( n16) k = min (n 10)

Retransmit the frame after r Exponential backoff algorithm

The random time delay is round-trip propagation delay r For 10BaseT 512 sr

36

CSMACD Random Time Delay (22)

Goal adapt retransmission attempts to estimated current load Heavy load random wait will be

longer

37

Examples of Binary Exponential Backoff Algorithm

First collision n=1 k=min(n10)=1 r 0 1 Probability=12 to send frame immediately Probability=12 to send frame after 512 s

Second collision n=2 k=min(n10)=2 r 0 1 2 3 Four cases 0s 512 s 512times2 s 512times3

s After ten collisions choose r from

01234hellip1023

38

Data Size Limitation

To avoid that any host occupies Ethernet too long the data size is smaller than 1500 bytes

If the size of a frame is too small adapters can not detect collision in time 10MHz 01sbit Within 512s 512sdivide01sbit= 512bits

=64 bytes can be sent Every frame must be larger than 64 bytes

Data size must be larger than 46 bytes

39

Effect of CSMACD

Unpredicable when the frame can be received

Not fair Bandwidth utilization degrades if heavy

loading Not suitable for real-time applications

40

Properties of An Ethernet

Shared bus technology( broadcast) Lowest level hardware does not support

addressing Best-effort delivery mechanism No central authority to grant access Each transmission is limited in duration

41

Part 4

IEEE 8023

42

IEEE 802 Series

Fiber UTP wireless cable

80211 8023

8022 LLC (Logic Link Control)

SMTP FTPHTTP

TCP UDP

SNMP DNS

IP

Ethernet802128024 8025

bull8023 CDMACD

bull8024 Token-bus

bull8025 Token-ring

bull80211 Wireless LAN

bull80212 100VG-AnyLAN

43

IEEE 8023 Protocol

Ethernet is compatible to 8023 Length of bytes in LLC

Preamble SourceDestination Length Data from LLC FCS

Bytes 8 6 6 2 46-1500 4

64-1518 bytes

44

Flow Chart of IEEE 8023傳送訊框

組成訊框

線上有訊號

訊框過短( )衝撞

檢查碼正確

傳送訊框

發生衝撞

傳送完畢

jamming送出signal

i=i+1

i gt 16

計算延遲時間

等待延遲時間

傳送失敗傳送成功

Y es

No

No

No

Y es

Y es Y es

No

接收訊框

開始接收

接收完畢

位址辨識成功

尚有多餘位元

刪除訊框頭尾

長度錯誤對齊錯誤

Y es

No

No

No

Y es

Y es

Y es

接收成功訊框錯誤

長度欄位內容正確

No

Y es No

Y es

No

Page 12: 1 Introduction of Ethernet Metcalfe’s Ethernet sketch Also refer to nfhuang/chap04.htm

12

Thin Ethernet with Repeater

3 segments connected by repeaters

terminator

repeater

Type-Tconnector

segment 1

segment 2

segment 3

兩終端電阻間最長不可超185 公尺 任兩台電腦間電

纜總長度不可超過 925 公尺

距離是05 公尺的倍數

任兩台電腦間不能超過4 個 repeater

13

10Base5 Bus Topology

terminator

repeater

Type-Tconnector

segment 1

segment 2

segment 3

兩終端電阻間最長不可超過500 公尺

任兩台電腦間電纜總長度不可超過 1500 公尺因此這 5 段同軸電纜不可以連接成一直線狀

最多 5 個 segment 任何二個工作站之間的路徑上最多只能有 2 個訊號增益器

14

10Base-T with Hub

10Base-T Centralized control by Hub

Still use Bus Topology - Broadcast Half duplex

One hub node crashes rarr Do not affect other nodes

Bus topology popular through mid 1990s All nodes in same collision domain (can

collide with each other)

HubHub

Hub

1

5

43

2 data

Hub

不可超過250 公尺

不可超過100 公尺

15

10Base-T with Switch

Centralized control by Switch Check the destination MAC address of Frame

forward this frame to a correct port No forward frames to other ports Full duplex Parallel sending many signals

Today star topology prevails Active switch in center Each ldquospokerdquo runs a (separate) Ethernet

protocol (nodes do not collide with each other)

SwitchSwitch

Switch

switchstar

16

Fast Ethernet 100BaseT Ethernet

100Mbps reduce the transmission delay of each bit

100BaseX uses 2 UTP pairs 100Base4T uses 4 UTP pairs Compatible to 10BaseT wiring system

frame format max packet size A bit transmission time is

1100M=001msec

17

Gigabit Ethernet IEEE 8023ab 1000Base-T IEEE 8023z

1000Base-SXLX Compatible to Ethernet Fast Ethernet

The same as old wiring system but speed is up to 1000Mbps

Use fiber of Category 5 UTP Used as a backbone or the

interconnection among servers

18

10 Gigabit Ethernet

IEEE 8023ae There are many differences between 8023ae

and old Ethernet specifications Use Optical Fiber Full-duplex

Have the same frame formatmax packet size Applications

Server interconnect for clusters of servers Links between switches and servers Backbone Very high-speed connections between buildings

19

Part 2

Ethernet Frame

20

Ethernet Unreliable Connectionless

Connectionless No handshaking between sending and receiving NICs NIC Network Interface Card

Unreliable receiving NIC doesnrsquot send acks or nacks to sending NIC Stream of datagrams passed to network layer

can have gaps (missing datagrams) Gaps will be filled if application is using TCP Otherwise application will see gaps

Ethernetrsquos MAC protocol unslotted CSMACD

21

Ethernet frame (13)

Define the frame in MAC layer Preamble

7 bytes with pattern 10101010 followed by one byte with pattern 10101011

Used to synchronize receiver sender clock rates

Preamble SourceDestination TypeData fromupper layer

FCS

Bytes 8 6 6 2 46-1500 4

64-1518 bytes

22

Ethernet frame (23)

Source MAC address Source accepts the data from upper layer

encapsulates as a frame then sends it to destination

Destination MAC address If adapter receives frame with matching

destination address or with broadcast address (eg ARP packet) it passes data in frame to network layer protocol Otherwise adapter discards frame

LSB=0 physical MAC address LSB=1 multicast address All 1s in 6 bytes broadcast address

23

Ethernet frame (33)

Type Indicates higher layer protocol

0800H IP 0600H XNS (Xerox protocol suit) Mostly IP but others possible eg Novell IPX

AppleTalk Data

46-1500 bytes Frame Check Sequence (FCS)

Checked at receiver If error is detected the frame is dropped

Use 32-bits CRC to check address type and data

24

Manchester Encoding

Each bit has a transition Allows clocks in sending and receiving

nodes to synchronize to each other No need for a centralized global clock among

nodes

-0225V 07V

-1825V -07V

for coaxial cable

for UTP

25

Round-trip Propagation Delay

The time delay to send a signal on one round-trip In specification the maximum distance

between 2 hosts is 2800m Use 10Mbps Ethernet as an example

Round-trip propagation delay is about 4638 s

Finally round-trip propagation delay is set to be 512 s

26

Thick Ethernet Topology

Max distance =500m3+1000m2+300m=2800m

訊號傳遞速度為光速的 065 倍 2800m2divide(3108

065)=2872s Round trip delay 還包括電纜線傳遞延遲及元件延遲等

source httpwwwcsnthuedutw~nfhuangchap04htm

27

Part 3

Multiple Access in

Ethernet

28

Sending an Ethernet Frame

Broadcast If there are two computers send data at

the same time two frames will collide A collision occurs Receivers discards these frames

CSMACD( Carrier Sense Multiple Access Collision Detection ) is used

Best Effect

29

CSMACD

Carrier Sense 表示網路卡要對 carrier 進行監測判斷網路線上是否有資料的傳送

Multiple Access 指出這種機制的目的是要讓多個網路卡可以在同一個 carrier 上存取資料

Collision Detection 表示 collision 是會發生的必須靠 detection的機制來判斷是否有 collision

30

Ethernet CSMACD algorithm (12)

1 NIC receives datagram from network layer and creates frame

2 If NIC senses channel idle starts frame transmission

If NIC senses channel busy waits until channel idle and then transmits

3 If NIC transmits entire frame without detecting another transmission NIC is done with frame

31

Ethernet CSMACD algorithm (22)

4 If NIC detects another transmission while transmitting aborts and sends jam signal Jam Signal make sure all other transmitters

are aware of collision 48 bits

5 After aborting NIC enters exponential backoff NIC chooses K at random from 012hellip2m-1

after the m th collision

NIC waits K512 bit times returns to Step 2

32

No Collision Occurs

A電腦 B電腦

A電腦 B電腦A frame開始送出

A電腦 B電腦

B聽到網路上有資 料 必須等待

A collision確定沒有繼續送資料

time=0

time=512s

Ex 10BaseT

why

33

Collision Occurs

If host B sends it frame before getting Arsquos frame a collision occurs

Host A finds noise treat it as a collision

The worst case A finds noise after a

round-trip propagation delay time

A電腦 B電腦B frame開始送出

A電腦 B電腦A frame開始送出

A電腦 B電腦collision發生

A電腦 B電腦

A collision發現接著送出

jamming signal

B collision發現

34

How Long to Find Collision

Round-trip propagation delay is 512 s for 10Mbps Ethernet

Host A must listen at least 512 s and know whether a collision occurs or not

A電腦 B電腦B frame開始送出

A電腦 B電腦A 開始送出

frame

A電腦 B電腦collision發生

A電腦 B電腦

A collision發現接著送出

Jamming signal

B collisionB發現 也 Jamming siganl會送

35

CSMACD Random Time Delay (12)

Let two collided hosts retransmit frames at a different time Host generates a random time delay (r) r 0

1 2k-1 n the number of collisions( n16) k = min (n 10)

Retransmit the frame after r Exponential backoff algorithm

The random time delay is round-trip propagation delay r For 10BaseT 512 sr

36

CSMACD Random Time Delay (22)

Goal adapt retransmission attempts to estimated current load Heavy load random wait will be

longer

37

Examples of Binary Exponential Backoff Algorithm

First collision n=1 k=min(n10)=1 r 0 1 Probability=12 to send frame immediately Probability=12 to send frame after 512 s

Second collision n=2 k=min(n10)=2 r 0 1 2 3 Four cases 0s 512 s 512times2 s 512times3

s After ten collisions choose r from

01234hellip1023

38

Data Size Limitation

To avoid that any host occupies Ethernet too long the data size is smaller than 1500 bytes

If the size of a frame is too small adapters can not detect collision in time 10MHz 01sbit Within 512s 512sdivide01sbit= 512bits

=64 bytes can be sent Every frame must be larger than 64 bytes

Data size must be larger than 46 bytes

39

Effect of CSMACD

Unpredicable when the frame can be received

Not fair Bandwidth utilization degrades if heavy

loading Not suitable for real-time applications

40

Properties of An Ethernet

Shared bus technology( broadcast) Lowest level hardware does not support

addressing Best-effort delivery mechanism No central authority to grant access Each transmission is limited in duration

41

Part 4

IEEE 8023

42

IEEE 802 Series

Fiber UTP wireless cable

80211 8023

8022 LLC (Logic Link Control)

SMTP FTPHTTP

TCP UDP

SNMP DNS

IP

Ethernet802128024 8025

bull8023 CDMACD

bull8024 Token-bus

bull8025 Token-ring

bull80211 Wireless LAN

bull80212 100VG-AnyLAN

43

IEEE 8023 Protocol

Ethernet is compatible to 8023 Length of bytes in LLC

Preamble SourceDestination Length Data from LLC FCS

Bytes 8 6 6 2 46-1500 4

64-1518 bytes

44

Flow Chart of IEEE 8023傳送訊框

組成訊框

線上有訊號

訊框過短( )衝撞

檢查碼正確

傳送訊框

發生衝撞

傳送完畢

jamming送出signal

i=i+1

i gt 16

計算延遲時間

等待延遲時間

傳送失敗傳送成功

Y es

No

No

No

Y es

Y es Y es

No

接收訊框

開始接收

接收完畢

位址辨識成功

尚有多餘位元

刪除訊框頭尾

長度錯誤對齊錯誤

Y es

No

No

No

Y es

Y es

Y es

接收成功訊框錯誤

長度欄位內容正確

No

Y es No

Y es

No

Page 13: 1 Introduction of Ethernet Metcalfe’s Ethernet sketch Also refer to nfhuang/chap04.htm

13

10Base5 Bus Topology

terminator

repeater

Type-Tconnector

segment 1

segment 2

segment 3

兩終端電阻間最長不可超過500 公尺

任兩台電腦間電纜總長度不可超過 1500 公尺因此這 5 段同軸電纜不可以連接成一直線狀

最多 5 個 segment 任何二個工作站之間的路徑上最多只能有 2 個訊號增益器

14

10Base-T with Hub

10Base-T Centralized control by Hub

Still use Bus Topology - Broadcast Half duplex

One hub node crashes rarr Do not affect other nodes

Bus topology popular through mid 1990s All nodes in same collision domain (can

collide with each other)

HubHub

Hub

1

5

43

2 data

Hub

不可超過250 公尺

不可超過100 公尺

15

10Base-T with Switch

Centralized control by Switch Check the destination MAC address of Frame

forward this frame to a correct port No forward frames to other ports Full duplex Parallel sending many signals

Today star topology prevails Active switch in center Each ldquospokerdquo runs a (separate) Ethernet

protocol (nodes do not collide with each other)

SwitchSwitch

Switch

switchstar

16

Fast Ethernet 100BaseT Ethernet

100Mbps reduce the transmission delay of each bit

100BaseX uses 2 UTP pairs 100Base4T uses 4 UTP pairs Compatible to 10BaseT wiring system

frame format max packet size A bit transmission time is

1100M=001msec

17

Gigabit Ethernet IEEE 8023ab 1000Base-T IEEE 8023z

1000Base-SXLX Compatible to Ethernet Fast Ethernet

The same as old wiring system but speed is up to 1000Mbps

Use fiber of Category 5 UTP Used as a backbone or the

interconnection among servers

18

10 Gigabit Ethernet

IEEE 8023ae There are many differences between 8023ae

and old Ethernet specifications Use Optical Fiber Full-duplex

Have the same frame formatmax packet size Applications

Server interconnect for clusters of servers Links between switches and servers Backbone Very high-speed connections between buildings

19

Part 2

Ethernet Frame

20

Ethernet Unreliable Connectionless

Connectionless No handshaking between sending and receiving NICs NIC Network Interface Card

Unreliable receiving NIC doesnrsquot send acks or nacks to sending NIC Stream of datagrams passed to network layer

can have gaps (missing datagrams) Gaps will be filled if application is using TCP Otherwise application will see gaps

Ethernetrsquos MAC protocol unslotted CSMACD

21

Ethernet frame (13)

Define the frame in MAC layer Preamble

7 bytes with pattern 10101010 followed by one byte with pattern 10101011

Used to synchronize receiver sender clock rates

Preamble SourceDestination TypeData fromupper layer

FCS

Bytes 8 6 6 2 46-1500 4

64-1518 bytes

22

Ethernet frame (23)

Source MAC address Source accepts the data from upper layer

encapsulates as a frame then sends it to destination

Destination MAC address If adapter receives frame with matching

destination address or with broadcast address (eg ARP packet) it passes data in frame to network layer protocol Otherwise adapter discards frame

LSB=0 physical MAC address LSB=1 multicast address All 1s in 6 bytes broadcast address

23

Ethernet frame (33)

Type Indicates higher layer protocol

0800H IP 0600H XNS (Xerox protocol suit) Mostly IP but others possible eg Novell IPX

AppleTalk Data

46-1500 bytes Frame Check Sequence (FCS)

Checked at receiver If error is detected the frame is dropped

Use 32-bits CRC to check address type and data

24

Manchester Encoding

Each bit has a transition Allows clocks in sending and receiving

nodes to synchronize to each other No need for a centralized global clock among

nodes

-0225V 07V

-1825V -07V

for coaxial cable

for UTP

25

Round-trip Propagation Delay

The time delay to send a signal on one round-trip In specification the maximum distance

between 2 hosts is 2800m Use 10Mbps Ethernet as an example

Round-trip propagation delay is about 4638 s

Finally round-trip propagation delay is set to be 512 s

26

Thick Ethernet Topology

Max distance =500m3+1000m2+300m=2800m

訊號傳遞速度為光速的 065 倍 2800m2divide(3108

065)=2872s Round trip delay 還包括電纜線傳遞延遲及元件延遲等

source httpwwwcsnthuedutw~nfhuangchap04htm

27

Part 3

Multiple Access in

Ethernet

28

Sending an Ethernet Frame

Broadcast If there are two computers send data at

the same time two frames will collide A collision occurs Receivers discards these frames

CSMACD( Carrier Sense Multiple Access Collision Detection ) is used

Best Effect

29

CSMACD

Carrier Sense 表示網路卡要對 carrier 進行監測判斷網路線上是否有資料的傳送

Multiple Access 指出這種機制的目的是要讓多個網路卡可以在同一個 carrier 上存取資料

Collision Detection 表示 collision 是會發生的必須靠 detection的機制來判斷是否有 collision

30

Ethernet CSMACD algorithm (12)

1 NIC receives datagram from network layer and creates frame

2 If NIC senses channel idle starts frame transmission

If NIC senses channel busy waits until channel idle and then transmits

3 If NIC transmits entire frame without detecting another transmission NIC is done with frame

31

Ethernet CSMACD algorithm (22)

4 If NIC detects another transmission while transmitting aborts and sends jam signal Jam Signal make sure all other transmitters

are aware of collision 48 bits

5 After aborting NIC enters exponential backoff NIC chooses K at random from 012hellip2m-1

after the m th collision

NIC waits K512 bit times returns to Step 2

32

No Collision Occurs

A電腦 B電腦

A電腦 B電腦A frame開始送出

A電腦 B電腦

B聽到網路上有資 料 必須等待

A collision確定沒有繼續送資料

time=0

time=512s

Ex 10BaseT

why

33

Collision Occurs

If host B sends it frame before getting Arsquos frame a collision occurs

Host A finds noise treat it as a collision

The worst case A finds noise after a

round-trip propagation delay time

A電腦 B電腦B frame開始送出

A電腦 B電腦A frame開始送出

A電腦 B電腦collision發生

A電腦 B電腦

A collision發現接著送出

jamming signal

B collision發現

34

How Long to Find Collision

Round-trip propagation delay is 512 s for 10Mbps Ethernet

Host A must listen at least 512 s and know whether a collision occurs or not

A電腦 B電腦B frame開始送出

A電腦 B電腦A 開始送出

frame

A電腦 B電腦collision發生

A電腦 B電腦

A collision發現接著送出

Jamming signal

B collisionB發現 也 Jamming siganl會送

35

CSMACD Random Time Delay (12)

Let two collided hosts retransmit frames at a different time Host generates a random time delay (r) r 0

1 2k-1 n the number of collisions( n16) k = min (n 10)

Retransmit the frame after r Exponential backoff algorithm

The random time delay is round-trip propagation delay r For 10BaseT 512 sr

36

CSMACD Random Time Delay (22)

Goal adapt retransmission attempts to estimated current load Heavy load random wait will be

longer

37

Examples of Binary Exponential Backoff Algorithm

First collision n=1 k=min(n10)=1 r 0 1 Probability=12 to send frame immediately Probability=12 to send frame after 512 s

Second collision n=2 k=min(n10)=2 r 0 1 2 3 Four cases 0s 512 s 512times2 s 512times3

s After ten collisions choose r from

01234hellip1023

38

Data Size Limitation

To avoid that any host occupies Ethernet too long the data size is smaller than 1500 bytes

If the size of a frame is too small adapters can not detect collision in time 10MHz 01sbit Within 512s 512sdivide01sbit= 512bits

=64 bytes can be sent Every frame must be larger than 64 bytes

Data size must be larger than 46 bytes

39

Effect of CSMACD

Unpredicable when the frame can be received

Not fair Bandwidth utilization degrades if heavy

loading Not suitable for real-time applications

40

Properties of An Ethernet

Shared bus technology( broadcast) Lowest level hardware does not support

addressing Best-effort delivery mechanism No central authority to grant access Each transmission is limited in duration

41

Part 4

IEEE 8023

42

IEEE 802 Series

Fiber UTP wireless cable

80211 8023

8022 LLC (Logic Link Control)

SMTP FTPHTTP

TCP UDP

SNMP DNS

IP

Ethernet802128024 8025

bull8023 CDMACD

bull8024 Token-bus

bull8025 Token-ring

bull80211 Wireless LAN

bull80212 100VG-AnyLAN

43

IEEE 8023 Protocol

Ethernet is compatible to 8023 Length of bytes in LLC

Preamble SourceDestination Length Data from LLC FCS

Bytes 8 6 6 2 46-1500 4

64-1518 bytes

44

Flow Chart of IEEE 8023傳送訊框

組成訊框

線上有訊號

訊框過短( )衝撞

檢查碼正確

傳送訊框

發生衝撞

傳送完畢

jamming送出signal

i=i+1

i gt 16

計算延遲時間

等待延遲時間

傳送失敗傳送成功

Y es

No

No

No

Y es

Y es Y es

No

接收訊框

開始接收

接收完畢

位址辨識成功

尚有多餘位元

刪除訊框頭尾

長度錯誤對齊錯誤

Y es

No

No

No

Y es

Y es

Y es

接收成功訊框錯誤

長度欄位內容正確

No

Y es No

Y es

No

Page 14: 1 Introduction of Ethernet Metcalfe’s Ethernet sketch Also refer to nfhuang/chap04.htm

14

10Base-T with Hub

10Base-T Centralized control by Hub

Still use Bus Topology - Broadcast Half duplex

One hub node crashes rarr Do not affect other nodes

Bus topology popular through mid 1990s All nodes in same collision domain (can

collide with each other)

HubHub

Hub

1

5

43

2 data

Hub

不可超過250 公尺

不可超過100 公尺

15

10Base-T with Switch

Centralized control by Switch Check the destination MAC address of Frame

forward this frame to a correct port No forward frames to other ports Full duplex Parallel sending many signals

Today star topology prevails Active switch in center Each ldquospokerdquo runs a (separate) Ethernet

protocol (nodes do not collide with each other)

SwitchSwitch

Switch

switchstar

16

Fast Ethernet 100BaseT Ethernet

100Mbps reduce the transmission delay of each bit

100BaseX uses 2 UTP pairs 100Base4T uses 4 UTP pairs Compatible to 10BaseT wiring system

frame format max packet size A bit transmission time is

1100M=001msec

17

Gigabit Ethernet IEEE 8023ab 1000Base-T IEEE 8023z

1000Base-SXLX Compatible to Ethernet Fast Ethernet

The same as old wiring system but speed is up to 1000Mbps

Use fiber of Category 5 UTP Used as a backbone or the

interconnection among servers

18

10 Gigabit Ethernet

IEEE 8023ae There are many differences between 8023ae

and old Ethernet specifications Use Optical Fiber Full-duplex

Have the same frame formatmax packet size Applications

Server interconnect for clusters of servers Links between switches and servers Backbone Very high-speed connections between buildings

19

Part 2

Ethernet Frame

20

Ethernet Unreliable Connectionless

Connectionless No handshaking between sending and receiving NICs NIC Network Interface Card

Unreliable receiving NIC doesnrsquot send acks or nacks to sending NIC Stream of datagrams passed to network layer

can have gaps (missing datagrams) Gaps will be filled if application is using TCP Otherwise application will see gaps

Ethernetrsquos MAC protocol unslotted CSMACD

21

Ethernet frame (13)

Define the frame in MAC layer Preamble

7 bytes with pattern 10101010 followed by one byte with pattern 10101011

Used to synchronize receiver sender clock rates

Preamble SourceDestination TypeData fromupper layer

FCS

Bytes 8 6 6 2 46-1500 4

64-1518 bytes

22

Ethernet frame (23)

Source MAC address Source accepts the data from upper layer

encapsulates as a frame then sends it to destination

Destination MAC address If adapter receives frame with matching

destination address or with broadcast address (eg ARP packet) it passes data in frame to network layer protocol Otherwise adapter discards frame

LSB=0 physical MAC address LSB=1 multicast address All 1s in 6 bytes broadcast address

23

Ethernet frame (33)

Type Indicates higher layer protocol

0800H IP 0600H XNS (Xerox protocol suit) Mostly IP but others possible eg Novell IPX

AppleTalk Data

46-1500 bytes Frame Check Sequence (FCS)

Checked at receiver If error is detected the frame is dropped

Use 32-bits CRC to check address type and data

24

Manchester Encoding

Each bit has a transition Allows clocks in sending and receiving

nodes to synchronize to each other No need for a centralized global clock among

nodes

-0225V 07V

-1825V -07V

for coaxial cable

for UTP

25

Round-trip Propagation Delay

The time delay to send a signal on one round-trip In specification the maximum distance

between 2 hosts is 2800m Use 10Mbps Ethernet as an example

Round-trip propagation delay is about 4638 s

Finally round-trip propagation delay is set to be 512 s

26

Thick Ethernet Topology

Max distance =500m3+1000m2+300m=2800m

訊號傳遞速度為光速的 065 倍 2800m2divide(3108

065)=2872s Round trip delay 還包括電纜線傳遞延遲及元件延遲等

source httpwwwcsnthuedutw~nfhuangchap04htm

27

Part 3

Multiple Access in

Ethernet

28

Sending an Ethernet Frame

Broadcast If there are two computers send data at

the same time two frames will collide A collision occurs Receivers discards these frames

CSMACD( Carrier Sense Multiple Access Collision Detection ) is used

Best Effect

29

CSMACD

Carrier Sense 表示網路卡要對 carrier 進行監測判斷網路線上是否有資料的傳送

Multiple Access 指出這種機制的目的是要讓多個網路卡可以在同一個 carrier 上存取資料

Collision Detection 表示 collision 是會發生的必須靠 detection的機制來判斷是否有 collision

30

Ethernet CSMACD algorithm (12)

1 NIC receives datagram from network layer and creates frame

2 If NIC senses channel idle starts frame transmission

If NIC senses channel busy waits until channel idle and then transmits

3 If NIC transmits entire frame without detecting another transmission NIC is done with frame

31

Ethernet CSMACD algorithm (22)

4 If NIC detects another transmission while transmitting aborts and sends jam signal Jam Signal make sure all other transmitters

are aware of collision 48 bits

5 After aborting NIC enters exponential backoff NIC chooses K at random from 012hellip2m-1

after the m th collision

NIC waits K512 bit times returns to Step 2

32

No Collision Occurs

A電腦 B電腦

A電腦 B電腦A frame開始送出

A電腦 B電腦

B聽到網路上有資 料 必須等待

A collision確定沒有繼續送資料

time=0

time=512s

Ex 10BaseT

why

33

Collision Occurs

If host B sends it frame before getting Arsquos frame a collision occurs

Host A finds noise treat it as a collision

The worst case A finds noise after a

round-trip propagation delay time

A電腦 B電腦B frame開始送出

A電腦 B電腦A frame開始送出

A電腦 B電腦collision發生

A電腦 B電腦

A collision發現接著送出

jamming signal

B collision發現

34

How Long to Find Collision

Round-trip propagation delay is 512 s for 10Mbps Ethernet

Host A must listen at least 512 s and know whether a collision occurs or not

A電腦 B電腦B frame開始送出

A電腦 B電腦A 開始送出

frame

A電腦 B電腦collision發生

A電腦 B電腦

A collision發現接著送出

Jamming signal

B collisionB發現 也 Jamming siganl會送

35

CSMACD Random Time Delay (12)

Let two collided hosts retransmit frames at a different time Host generates a random time delay (r) r 0

1 2k-1 n the number of collisions( n16) k = min (n 10)

Retransmit the frame after r Exponential backoff algorithm

The random time delay is round-trip propagation delay r For 10BaseT 512 sr

36

CSMACD Random Time Delay (22)

Goal adapt retransmission attempts to estimated current load Heavy load random wait will be

longer

37

Examples of Binary Exponential Backoff Algorithm

First collision n=1 k=min(n10)=1 r 0 1 Probability=12 to send frame immediately Probability=12 to send frame after 512 s

Second collision n=2 k=min(n10)=2 r 0 1 2 3 Four cases 0s 512 s 512times2 s 512times3

s After ten collisions choose r from

01234hellip1023

38

Data Size Limitation

To avoid that any host occupies Ethernet too long the data size is smaller than 1500 bytes

If the size of a frame is too small adapters can not detect collision in time 10MHz 01sbit Within 512s 512sdivide01sbit= 512bits

=64 bytes can be sent Every frame must be larger than 64 bytes

Data size must be larger than 46 bytes

39

Effect of CSMACD

Unpredicable when the frame can be received

Not fair Bandwidth utilization degrades if heavy

loading Not suitable for real-time applications

40

Properties of An Ethernet

Shared bus technology( broadcast) Lowest level hardware does not support

addressing Best-effort delivery mechanism No central authority to grant access Each transmission is limited in duration

41

Part 4

IEEE 8023

42

IEEE 802 Series

Fiber UTP wireless cable

80211 8023

8022 LLC (Logic Link Control)

SMTP FTPHTTP

TCP UDP

SNMP DNS

IP

Ethernet802128024 8025

bull8023 CDMACD

bull8024 Token-bus

bull8025 Token-ring

bull80211 Wireless LAN

bull80212 100VG-AnyLAN

43

IEEE 8023 Protocol

Ethernet is compatible to 8023 Length of bytes in LLC

Preamble SourceDestination Length Data from LLC FCS

Bytes 8 6 6 2 46-1500 4

64-1518 bytes

44

Flow Chart of IEEE 8023傳送訊框

組成訊框

線上有訊號

訊框過短( )衝撞

檢查碼正確

傳送訊框

發生衝撞

傳送完畢

jamming送出signal

i=i+1

i gt 16

計算延遲時間

等待延遲時間

傳送失敗傳送成功

Y es

No

No

No

Y es

Y es Y es

No

接收訊框

開始接收

接收完畢

位址辨識成功

尚有多餘位元

刪除訊框頭尾

長度錯誤對齊錯誤

Y es

No

No

No

Y es

Y es

Y es

接收成功訊框錯誤

長度欄位內容正確

No

Y es No

Y es

No

Page 15: 1 Introduction of Ethernet Metcalfe’s Ethernet sketch Also refer to nfhuang/chap04.htm

15

10Base-T with Switch

Centralized control by Switch Check the destination MAC address of Frame

forward this frame to a correct port No forward frames to other ports Full duplex Parallel sending many signals

Today star topology prevails Active switch in center Each ldquospokerdquo runs a (separate) Ethernet

protocol (nodes do not collide with each other)

SwitchSwitch

Switch

switchstar

16

Fast Ethernet 100BaseT Ethernet

100Mbps reduce the transmission delay of each bit

100BaseX uses 2 UTP pairs 100Base4T uses 4 UTP pairs Compatible to 10BaseT wiring system

frame format max packet size A bit transmission time is

1100M=001msec

17

Gigabit Ethernet IEEE 8023ab 1000Base-T IEEE 8023z

1000Base-SXLX Compatible to Ethernet Fast Ethernet

The same as old wiring system but speed is up to 1000Mbps

Use fiber of Category 5 UTP Used as a backbone or the

interconnection among servers

18

10 Gigabit Ethernet

IEEE 8023ae There are many differences between 8023ae

and old Ethernet specifications Use Optical Fiber Full-duplex

Have the same frame formatmax packet size Applications

Server interconnect for clusters of servers Links between switches and servers Backbone Very high-speed connections between buildings

19

Part 2

Ethernet Frame

20

Ethernet Unreliable Connectionless

Connectionless No handshaking between sending and receiving NICs NIC Network Interface Card

Unreliable receiving NIC doesnrsquot send acks or nacks to sending NIC Stream of datagrams passed to network layer

can have gaps (missing datagrams) Gaps will be filled if application is using TCP Otherwise application will see gaps

Ethernetrsquos MAC protocol unslotted CSMACD

21

Ethernet frame (13)

Define the frame in MAC layer Preamble

7 bytes with pattern 10101010 followed by one byte with pattern 10101011

Used to synchronize receiver sender clock rates

Preamble SourceDestination TypeData fromupper layer

FCS

Bytes 8 6 6 2 46-1500 4

64-1518 bytes

22

Ethernet frame (23)

Source MAC address Source accepts the data from upper layer

encapsulates as a frame then sends it to destination

Destination MAC address If adapter receives frame with matching

destination address or with broadcast address (eg ARP packet) it passes data in frame to network layer protocol Otherwise adapter discards frame

LSB=0 physical MAC address LSB=1 multicast address All 1s in 6 bytes broadcast address

23

Ethernet frame (33)

Type Indicates higher layer protocol

0800H IP 0600H XNS (Xerox protocol suit) Mostly IP but others possible eg Novell IPX

AppleTalk Data

46-1500 bytes Frame Check Sequence (FCS)

Checked at receiver If error is detected the frame is dropped

Use 32-bits CRC to check address type and data

24

Manchester Encoding

Each bit has a transition Allows clocks in sending and receiving

nodes to synchronize to each other No need for a centralized global clock among

nodes

-0225V 07V

-1825V -07V

for coaxial cable

for UTP

25

Round-trip Propagation Delay

The time delay to send a signal on one round-trip In specification the maximum distance

between 2 hosts is 2800m Use 10Mbps Ethernet as an example

Round-trip propagation delay is about 4638 s

Finally round-trip propagation delay is set to be 512 s

26

Thick Ethernet Topology

Max distance =500m3+1000m2+300m=2800m

訊號傳遞速度為光速的 065 倍 2800m2divide(3108

065)=2872s Round trip delay 還包括電纜線傳遞延遲及元件延遲等

source httpwwwcsnthuedutw~nfhuangchap04htm

27

Part 3

Multiple Access in

Ethernet

28

Sending an Ethernet Frame

Broadcast If there are two computers send data at

the same time two frames will collide A collision occurs Receivers discards these frames

CSMACD( Carrier Sense Multiple Access Collision Detection ) is used

Best Effect

29

CSMACD

Carrier Sense 表示網路卡要對 carrier 進行監測判斷網路線上是否有資料的傳送

Multiple Access 指出這種機制的目的是要讓多個網路卡可以在同一個 carrier 上存取資料

Collision Detection 表示 collision 是會發生的必須靠 detection的機制來判斷是否有 collision

30

Ethernet CSMACD algorithm (12)

1 NIC receives datagram from network layer and creates frame

2 If NIC senses channel idle starts frame transmission

If NIC senses channel busy waits until channel idle and then transmits

3 If NIC transmits entire frame without detecting another transmission NIC is done with frame

31

Ethernet CSMACD algorithm (22)

4 If NIC detects another transmission while transmitting aborts and sends jam signal Jam Signal make sure all other transmitters

are aware of collision 48 bits

5 After aborting NIC enters exponential backoff NIC chooses K at random from 012hellip2m-1

after the m th collision

NIC waits K512 bit times returns to Step 2

32

No Collision Occurs

A電腦 B電腦

A電腦 B電腦A frame開始送出

A電腦 B電腦

B聽到網路上有資 料 必須等待

A collision確定沒有繼續送資料

time=0

time=512s

Ex 10BaseT

why

33

Collision Occurs

If host B sends it frame before getting Arsquos frame a collision occurs

Host A finds noise treat it as a collision

The worst case A finds noise after a

round-trip propagation delay time

A電腦 B電腦B frame開始送出

A電腦 B電腦A frame開始送出

A電腦 B電腦collision發生

A電腦 B電腦

A collision發現接著送出

jamming signal

B collision發現

34

How Long to Find Collision

Round-trip propagation delay is 512 s for 10Mbps Ethernet

Host A must listen at least 512 s and know whether a collision occurs or not

A電腦 B電腦B frame開始送出

A電腦 B電腦A 開始送出

frame

A電腦 B電腦collision發生

A電腦 B電腦

A collision發現接著送出

Jamming signal

B collisionB發現 也 Jamming siganl會送

35

CSMACD Random Time Delay (12)

Let two collided hosts retransmit frames at a different time Host generates a random time delay (r) r 0

1 2k-1 n the number of collisions( n16) k = min (n 10)

Retransmit the frame after r Exponential backoff algorithm

The random time delay is round-trip propagation delay r For 10BaseT 512 sr

36

CSMACD Random Time Delay (22)

Goal adapt retransmission attempts to estimated current load Heavy load random wait will be

longer

37

Examples of Binary Exponential Backoff Algorithm

First collision n=1 k=min(n10)=1 r 0 1 Probability=12 to send frame immediately Probability=12 to send frame after 512 s

Second collision n=2 k=min(n10)=2 r 0 1 2 3 Four cases 0s 512 s 512times2 s 512times3

s After ten collisions choose r from

01234hellip1023

38

Data Size Limitation

To avoid that any host occupies Ethernet too long the data size is smaller than 1500 bytes

If the size of a frame is too small adapters can not detect collision in time 10MHz 01sbit Within 512s 512sdivide01sbit= 512bits

=64 bytes can be sent Every frame must be larger than 64 bytes

Data size must be larger than 46 bytes

39

Effect of CSMACD

Unpredicable when the frame can be received

Not fair Bandwidth utilization degrades if heavy

loading Not suitable for real-time applications

40

Properties of An Ethernet

Shared bus technology( broadcast) Lowest level hardware does not support

addressing Best-effort delivery mechanism No central authority to grant access Each transmission is limited in duration

41

Part 4

IEEE 8023

42

IEEE 802 Series

Fiber UTP wireless cable

80211 8023

8022 LLC (Logic Link Control)

SMTP FTPHTTP

TCP UDP

SNMP DNS

IP

Ethernet802128024 8025

bull8023 CDMACD

bull8024 Token-bus

bull8025 Token-ring

bull80211 Wireless LAN

bull80212 100VG-AnyLAN

43

IEEE 8023 Protocol

Ethernet is compatible to 8023 Length of bytes in LLC

Preamble SourceDestination Length Data from LLC FCS

Bytes 8 6 6 2 46-1500 4

64-1518 bytes

44

Flow Chart of IEEE 8023傳送訊框

組成訊框

線上有訊號

訊框過短( )衝撞

檢查碼正確

傳送訊框

發生衝撞

傳送完畢

jamming送出signal

i=i+1

i gt 16

計算延遲時間

等待延遲時間

傳送失敗傳送成功

Y es

No

No

No

Y es

Y es Y es

No

接收訊框

開始接收

接收完畢

位址辨識成功

尚有多餘位元

刪除訊框頭尾

長度錯誤對齊錯誤

Y es

No

No

No

Y es

Y es

Y es

接收成功訊框錯誤

長度欄位內容正確

No

Y es No

Y es

No

Page 16: 1 Introduction of Ethernet Metcalfe’s Ethernet sketch Also refer to nfhuang/chap04.htm

16

Fast Ethernet 100BaseT Ethernet

100Mbps reduce the transmission delay of each bit

100BaseX uses 2 UTP pairs 100Base4T uses 4 UTP pairs Compatible to 10BaseT wiring system

frame format max packet size A bit transmission time is

1100M=001msec

17

Gigabit Ethernet IEEE 8023ab 1000Base-T IEEE 8023z

1000Base-SXLX Compatible to Ethernet Fast Ethernet

The same as old wiring system but speed is up to 1000Mbps

Use fiber of Category 5 UTP Used as a backbone or the

interconnection among servers

18

10 Gigabit Ethernet

IEEE 8023ae There are many differences between 8023ae

and old Ethernet specifications Use Optical Fiber Full-duplex

Have the same frame formatmax packet size Applications

Server interconnect for clusters of servers Links between switches and servers Backbone Very high-speed connections between buildings

19

Part 2

Ethernet Frame

20

Ethernet Unreliable Connectionless

Connectionless No handshaking between sending and receiving NICs NIC Network Interface Card

Unreliable receiving NIC doesnrsquot send acks or nacks to sending NIC Stream of datagrams passed to network layer

can have gaps (missing datagrams) Gaps will be filled if application is using TCP Otherwise application will see gaps

Ethernetrsquos MAC protocol unslotted CSMACD

21

Ethernet frame (13)

Define the frame in MAC layer Preamble

7 bytes with pattern 10101010 followed by one byte with pattern 10101011

Used to synchronize receiver sender clock rates

Preamble SourceDestination TypeData fromupper layer

FCS

Bytes 8 6 6 2 46-1500 4

64-1518 bytes

22

Ethernet frame (23)

Source MAC address Source accepts the data from upper layer

encapsulates as a frame then sends it to destination

Destination MAC address If adapter receives frame with matching

destination address or with broadcast address (eg ARP packet) it passes data in frame to network layer protocol Otherwise adapter discards frame

LSB=0 physical MAC address LSB=1 multicast address All 1s in 6 bytes broadcast address

23

Ethernet frame (33)

Type Indicates higher layer protocol

0800H IP 0600H XNS (Xerox protocol suit) Mostly IP but others possible eg Novell IPX

AppleTalk Data

46-1500 bytes Frame Check Sequence (FCS)

Checked at receiver If error is detected the frame is dropped

Use 32-bits CRC to check address type and data

24

Manchester Encoding

Each bit has a transition Allows clocks in sending and receiving

nodes to synchronize to each other No need for a centralized global clock among

nodes

-0225V 07V

-1825V -07V

for coaxial cable

for UTP

25

Round-trip Propagation Delay

The time delay to send a signal on one round-trip In specification the maximum distance

between 2 hosts is 2800m Use 10Mbps Ethernet as an example

Round-trip propagation delay is about 4638 s

Finally round-trip propagation delay is set to be 512 s

26

Thick Ethernet Topology

Max distance =500m3+1000m2+300m=2800m

訊號傳遞速度為光速的 065 倍 2800m2divide(3108

065)=2872s Round trip delay 還包括電纜線傳遞延遲及元件延遲等

source httpwwwcsnthuedutw~nfhuangchap04htm

27

Part 3

Multiple Access in

Ethernet

28

Sending an Ethernet Frame

Broadcast If there are two computers send data at

the same time two frames will collide A collision occurs Receivers discards these frames

CSMACD( Carrier Sense Multiple Access Collision Detection ) is used

Best Effect

29

CSMACD

Carrier Sense 表示網路卡要對 carrier 進行監測判斷網路線上是否有資料的傳送

Multiple Access 指出這種機制的目的是要讓多個網路卡可以在同一個 carrier 上存取資料

Collision Detection 表示 collision 是會發生的必須靠 detection的機制來判斷是否有 collision

30

Ethernet CSMACD algorithm (12)

1 NIC receives datagram from network layer and creates frame

2 If NIC senses channel idle starts frame transmission

If NIC senses channel busy waits until channel idle and then transmits

3 If NIC transmits entire frame without detecting another transmission NIC is done with frame

31

Ethernet CSMACD algorithm (22)

4 If NIC detects another transmission while transmitting aborts and sends jam signal Jam Signal make sure all other transmitters

are aware of collision 48 bits

5 After aborting NIC enters exponential backoff NIC chooses K at random from 012hellip2m-1

after the m th collision

NIC waits K512 bit times returns to Step 2

32

No Collision Occurs

A電腦 B電腦

A電腦 B電腦A frame開始送出

A電腦 B電腦

B聽到網路上有資 料 必須等待

A collision確定沒有繼續送資料

time=0

time=512s

Ex 10BaseT

why

33

Collision Occurs

If host B sends it frame before getting Arsquos frame a collision occurs

Host A finds noise treat it as a collision

The worst case A finds noise after a

round-trip propagation delay time

A電腦 B電腦B frame開始送出

A電腦 B電腦A frame開始送出

A電腦 B電腦collision發生

A電腦 B電腦

A collision發現接著送出

jamming signal

B collision發現

34

How Long to Find Collision

Round-trip propagation delay is 512 s for 10Mbps Ethernet

Host A must listen at least 512 s and know whether a collision occurs or not

A電腦 B電腦B frame開始送出

A電腦 B電腦A 開始送出

frame

A電腦 B電腦collision發生

A電腦 B電腦

A collision發現接著送出

Jamming signal

B collisionB發現 也 Jamming siganl會送

35

CSMACD Random Time Delay (12)

Let two collided hosts retransmit frames at a different time Host generates a random time delay (r) r 0

1 2k-1 n the number of collisions( n16) k = min (n 10)

Retransmit the frame after r Exponential backoff algorithm

The random time delay is round-trip propagation delay r For 10BaseT 512 sr

36

CSMACD Random Time Delay (22)

Goal adapt retransmission attempts to estimated current load Heavy load random wait will be

longer

37

Examples of Binary Exponential Backoff Algorithm

First collision n=1 k=min(n10)=1 r 0 1 Probability=12 to send frame immediately Probability=12 to send frame after 512 s

Second collision n=2 k=min(n10)=2 r 0 1 2 3 Four cases 0s 512 s 512times2 s 512times3

s After ten collisions choose r from

01234hellip1023

38

Data Size Limitation

To avoid that any host occupies Ethernet too long the data size is smaller than 1500 bytes

If the size of a frame is too small adapters can not detect collision in time 10MHz 01sbit Within 512s 512sdivide01sbit= 512bits

=64 bytes can be sent Every frame must be larger than 64 bytes

Data size must be larger than 46 bytes

39

Effect of CSMACD

Unpredicable when the frame can be received

Not fair Bandwidth utilization degrades if heavy

loading Not suitable for real-time applications

40

Properties of An Ethernet

Shared bus technology( broadcast) Lowest level hardware does not support

addressing Best-effort delivery mechanism No central authority to grant access Each transmission is limited in duration

41

Part 4

IEEE 8023

42

IEEE 802 Series

Fiber UTP wireless cable

80211 8023

8022 LLC (Logic Link Control)

SMTP FTPHTTP

TCP UDP

SNMP DNS

IP

Ethernet802128024 8025

bull8023 CDMACD

bull8024 Token-bus

bull8025 Token-ring

bull80211 Wireless LAN

bull80212 100VG-AnyLAN

43

IEEE 8023 Protocol

Ethernet is compatible to 8023 Length of bytes in LLC

Preamble SourceDestination Length Data from LLC FCS

Bytes 8 6 6 2 46-1500 4

64-1518 bytes

44

Flow Chart of IEEE 8023傳送訊框

組成訊框

線上有訊號

訊框過短( )衝撞

檢查碼正確

傳送訊框

發生衝撞

傳送完畢

jamming送出signal

i=i+1

i gt 16

計算延遲時間

等待延遲時間

傳送失敗傳送成功

Y es

No

No

No

Y es

Y es Y es

No

接收訊框

開始接收

接收完畢

位址辨識成功

尚有多餘位元

刪除訊框頭尾

長度錯誤對齊錯誤

Y es

No

No

No

Y es

Y es

Y es

接收成功訊框錯誤

長度欄位內容正確

No

Y es No

Y es

No

Page 17: 1 Introduction of Ethernet Metcalfe’s Ethernet sketch Also refer to nfhuang/chap04.htm

17

Gigabit Ethernet IEEE 8023ab 1000Base-T IEEE 8023z

1000Base-SXLX Compatible to Ethernet Fast Ethernet

The same as old wiring system but speed is up to 1000Mbps

Use fiber of Category 5 UTP Used as a backbone or the

interconnection among servers

18

10 Gigabit Ethernet

IEEE 8023ae There are many differences between 8023ae

and old Ethernet specifications Use Optical Fiber Full-duplex

Have the same frame formatmax packet size Applications

Server interconnect for clusters of servers Links between switches and servers Backbone Very high-speed connections between buildings

19

Part 2

Ethernet Frame

20

Ethernet Unreliable Connectionless

Connectionless No handshaking between sending and receiving NICs NIC Network Interface Card

Unreliable receiving NIC doesnrsquot send acks or nacks to sending NIC Stream of datagrams passed to network layer

can have gaps (missing datagrams) Gaps will be filled if application is using TCP Otherwise application will see gaps

Ethernetrsquos MAC protocol unslotted CSMACD

21

Ethernet frame (13)

Define the frame in MAC layer Preamble

7 bytes with pattern 10101010 followed by one byte with pattern 10101011

Used to synchronize receiver sender clock rates

Preamble SourceDestination TypeData fromupper layer

FCS

Bytes 8 6 6 2 46-1500 4

64-1518 bytes

22

Ethernet frame (23)

Source MAC address Source accepts the data from upper layer

encapsulates as a frame then sends it to destination

Destination MAC address If adapter receives frame with matching

destination address or with broadcast address (eg ARP packet) it passes data in frame to network layer protocol Otherwise adapter discards frame

LSB=0 physical MAC address LSB=1 multicast address All 1s in 6 bytes broadcast address

23

Ethernet frame (33)

Type Indicates higher layer protocol

0800H IP 0600H XNS (Xerox protocol suit) Mostly IP but others possible eg Novell IPX

AppleTalk Data

46-1500 bytes Frame Check Sequence (FCS)

Checked at receiver If error is detected the frame is dropped

Use 32-bits CRC to check address type and data

24

Manchester Encoding

Each bit has a transition Allows clocks in sending and receiving

nodes to synchronize to each other No need for a centralized global clock among

nodes

-0225V 07V

-1825V -07V

for coaxial cable

for UTP

25

Round-trip Propagation Delay

The time delay to send a signal on one round-trip In specification the maximum distance

between 2 hosts is 2800m Use 10Mbps Ethernet as an example

Round-trip propagation delay is about 4638 s

Finally round-trip propagation delay is set to be 512 s

26

Thick Ethernet Topology

Max distance =500m3+1000m2+300m=2800m

訊號傳遞速度為光速的 065 倍 2800m2divide(3108

065)=2872s Round trip delay 還包括電纜線傳遞延遲及元件延遲等

source httpwwwcsnthuedutw~nfhuangchap04htm

27

Part 3

Multiple Access in

Ethernet

28

Sending an Ethernet Frame

Broadcast If there are two computers send data at

the same time two frames will collide A collision occurs Receivers discards these frames

CSMACD( Carrier Sense Multiple Access Collision Detection ) is used

Best Effect

29

CSMACD

Carrier Sense 表示網路卡要對 carrier 進行監測判斷網路線上是否有資料的傳送

Multiple Access 指出這種機制的目的是要讓多個網路卡可以在同一個 carrier 上存取資料

Collision Detection 表示 collision 是會發生的必須靠 detection的機制來判斷是否有 collision

30

Ethernet CSMACD algorithm (12)

1 NIC receives datagram from network layer and creates frame

2 If NIC senses channel idle starts frame transmission

If NIC senses channel busy waits until channel idle and then transmits

3 If NIC transmits entire frame without detecting another transmission NIC is done with frame

31

Ethernet CSMACD algorithm (22)

4 If NIC detects another transmission while transmitting aborts and sends jam signal Jam Signal make sure all other transmitters

are aware of collision 48 bits

5 After aborting NIC enters exponential backoff NIC chooses K at random from 012hellip2m-1

after the m th collision

NIC waits K512 bit times returns to Step 2

32

No Collision Occurs

A電腦 B電腦

A電腦 B電腦A frame開始送出

A電腦 B電腦

B聽到網路上有資 料 必須等待

A collision確定沒有繼續送資料

time=0

time=512s

Ex 10BaseT

why

33

Collision Occurs

If host B sends it frame before getting Arsquos frame a collision occurs

Host A finds noise treat it as a collision

The worst case A finds noise after a

round-trip propagation delay time

A電腦 B電腦B frame開始送出

A電腦 B電腦A frame開始送出

A電腦 B電腦collision發生

A電腦 B電腦

A collision發現接著送出

jamming signal

B collision發現

34

How Long to Find Collision

Round-trip propagation delay is 512 s for 10Mbps Ethernet

Host A must listen at least 512 s and know whether a collision occurs or not

A電腦 B電腦B frame開始送出

A電腦 B電腦A 開始送出

frame

A電腦 B電腦collision發生

A電腦 B電腦

A collision發現接著送出

Jamming signal

B collisionB發現 也 Jamming siganl會送

35

CSMACD Random Time Delay (12)

Let two collided hosts retransmit frames at a different time Host generates a random time delay (r) r 0

1 2k-1 n the number of collisions( n16) k = min (n 10)

Retransmit the frame after r Exponential backoff algorithm

The random time delay is round-trip propagation delay r For 10BaseT 512 sr

36

CSMACD Random Time Delay (22)

Goal adapt retransmission attempts to estimated current load Heavy load random wait will be

longer

37

Examples of Binary Exponential Backoff Algorithm

First collision n=1 k=min(n10)=1 r 0 1 Probability=12 to send frame immediately Probability=12 to send frame after 512 s

Second collision n=2 k=min(n10)=2 r 0 1 2 3 Four cases 0s 512 s 512times2 s 512times3

s After ten collisions choose r from

01234hellip1023

38

Data Size Limitation

To avoid that any host occupies Ethernet too long the data size is smaller than 1500 bytes

If the size of a frame is too small adapters can not detect collision in time 10MHz 01sbit Within 512s 512sdivide01sbit= 512bits

=64 bytes can be sent Every frame must be larger than 64 bytes

Data size must be larger than 46 bytes

39

Effect of CSMACD

Unpredicable when the frame can be received

Not fair Bandwidth utilization degrades if heavy

loading Not suitable for real-time applications

40

Properties of An Ethernet

Shared bus technology( broadcast) Lowest level hardware does not support

addressing Best-effort delivery mechanism No central authority to grant access Each transmission is limited in duration

41

Part 4

IEEE 8023

42

IEEE 802 Series

Fiber UTP wireless cable

80211 8023

8022 LLC (Logic Link Control)

SMTP FTPHTTP

TCP UDP

SNMP DNS

IP

Ethernet802128024 8025

bull8023 CDMACD

bull8024 Token-bus

bull8025 Token-ring

bull80211 Wireless LAN

bull80212 100VG-AnyLAN

43

IEEE 8023 Protocol

Ethernet is compatible to 8023 Length of bytes in LLC

Preamble SourceDestination Length Data from LLC FCS

Bytes 8 6 6 2 46-1500 4

64-1518 bytes

44

Flow Chart of IEEE 8023傳送訊框

組成訊框

線上有訊號

訊框過短( )衝撞

檢查碼正確

傳送訊框

發生衝撞

傳送完畢

jamming送出signal

i=i+1

i gt 16

計算延遲時間

等待延遲時間

傳送失敗傳送成功

Y es

No

No

No

Y es

Y es Y es

No

接收訊框

開始接收

接收完畢

位址辨識成功

尚有多餘位元

刪除訊框頭尾

長度錯誤對齊錯誤

Y es

No

No

No

Y es

Y es

Y es

接收成功訊框錯誤

長度欄位內容正確

No

Y es No

Y es

No

Page 18: 1 Introduction of Ethernet Metcalfe’s Ethernet sketch Also refer to nfhuang/chap04.htm

18

10 Gigabit Ethernet

IEEE 8023ae There are many differences between 8023ae

and old Ethernet specifications Use Optical Fiber Full-duplex

Have the same frame formatmax packet size Applications

Server interconnect for clusters of servers Links between switches and servers Backbone Very high-speed connections between buildings

19

Part 2

Ethernet Frame

20

Ethernet Unreliable Connectionless

Connectionless No handshaking between sending and receiving NICs NIC Network Interface Card

Unreliable receiving NIC doesnrsquot send acks or nacks to sending NIC Stream of datagrams passed to network layer

can have gaps (missing datagrams) Gaps will be filled if application is using TCP Otherwise application will see gaps

Ethernetrsquos MAC protocol unslotted CSMACD

21

Ethernet frame (13)

Define the frame in MAC layer Preamble

7 bytes with pattern 10101010 followed by one byte with pattern 10101011

Used to synchronize receiver sender clock rates

Preamble SourceDestination TypeData fromupper layer

FCS

Bytes 8 6 6 2 46-1500 4

64-1518 bytes

22

Ethernet frame (23)

Source MAC address Source accepts the data from upper layer

encapsulates as a frame then sends it to destination

Destination MAC address If adapter receives frame with matching

destination address or with broadcast address (eg ARP packet) it passes data in frame to network layer protocol Otherwise adapter discards frame

LSB=0 physical MAC address LSB=1 multicast address All 1s in 6 bytes broadcast address

23

Ethernet frame (33)

Type Indicates higher layer protocol

0800H IP 0600H XNS (Xerox protocol suit) Mostly IP but others possible eg Novell IPX

AppleTalk Data

46-1500 bytes Frame Check Sequence (FCS)

Checked at receiver If error is detected the frame is dropped

Use 32-bits CRC to check address type and data

24

Manchester Encoding

Each bit has a transition Allows clocks in sending and receiving

nodes to synchronize to each other No need for a centralized global clock among

nodes

-0225V 07V

-1825V -07V

for coaxial cable

for UTP

25

Round-trip Propagation Delay

The time delay to send a signal on one round-trip In specification the maximum distance

between 2 hosts is 2800m Use 10Mbps Ethernet as an example

Round-trip propagation delay is about 4638 s

Finally round-trip propagation delay is set to be 512 s

26

Thick Ethernet Topology

Max distance =500m3+1000m2+300m=2800m

訊號傳遞速度為光速的 065 倍 2800m2divide(3108

065)=2872s Round trip delay 還包括電纜線傳遞延遲及元件延遲等

source httpwwwcsnthuedutw~nfhuangchap04htm

27

Part 3

Multiple Access in

Ethernet

28

Sending an Ethernet Frame

Broadcast If there are two computers send data at

the same time two frames will collide A collision occurs Receivers discards these frames

CSMACD( Carrier Sense Multiple Access Collision Detection ) is used

Best Effect

29

CSMACD

Carrier Sense 表示網路卡要對 carrier 進行監測判斷網路線上是否有資料的傳送

Multiple Access 指出這種機制的目的是要讓多個網路卡可以在同一個 carrier 上存取資料

Collision Detection 表示 collision 是會發生的必須靠 detection的機制來判斷是否有 collision

30

Ethernet CSMACD algorithm (12)

1 NIC receives datagram from network layer and creates frame

2 If NIC senses channel idle starts frame transmission

If NIC senses channel busy waits until channel idle and then transmits

3 If NIC transmits entire frame without detecting another transmission NIC is done with frame

31

Ethernet CSMACD algorithm (22)

4 If NIC detects another transmission while transmitting aborts and sends jam signal Jam Signal make sure all other transmitters

are aware of collision 48 bits

5 After aborting NIC enters exponential backoff NIC chooses K at random from 012hellip2m-1

after the m th collision

NIC waits K512 bit times returns to Step 2

32

No Collision Occurs

A電腦 B電腦

A電腦 B電腦A frame開始送出

A電腦 B電腦

B聽到網路上有資 料 必須等待

A collision確定沒有繼續送資料

time=0

time=512s

Ex 10BaseT

why

33

Collision Occurs

If host B sends it frame before getting Arsquos frame a collision occurs

Host A finds noise treat it as a collision

The worst case A finds noise after a

round-trip propagation delay time

A電腦 B電腦B frame開始送出

A電腦 B電腦A frame開始送出

A電腦 B電腦collision發生

A電腦 B電腦

A collision發現接著送出

jamming signal

B collision發現

34

How Long to Find Collision

Round-trip propagation delay is 512 s for 10Mbps Ethernet

Host A must listen at least 512 s and know whether a collision occurs or not

A電腦 B電腦B frame開始送出

A電腦 B電腦A 開始送出

frame

A電腦 B電腦collision發生

A電腦 B電腦

A collision發現接著送出

Jamming signal

B collisionB發現 也 Jamming siganl會送

35

CSMACD Random Time Delay (12)

Let two collided hosts retransmit frames at a different time Host generates a random time delay (r) r 0

1 2k-1 n the number of collisions( n16) k = min (n 10)

Retransmit the frame after r Exponential backoff algorithm

The random time delay is round-trip propagation delay r For 10BaseT 512 sr

36

CSMACD Random Time Delay (22)

Goal adapt retransmission attempts to estimated current load Heavy load random wait will be

longer

37

Examples of Binary Exponential Backoff Algorithm

First collision n=1 k=min(n10)=1 r 0 1 Probability=12 to send frame immediately Probability=12 to send frame after 512 s

Second collision n=2 k=min(n10)=2 r 0 1 2 3 Four cases 0s 512 s 512times2 s 512times3

s After ten collisions choose r from

01234hellip1023

38

Data Size Limitation

To avoid that any host occupies Ethernet too long the data size is smaller than 1500 bytes

If the size of a frame is too small adapters can not detect collision in time 10MHz 01sbit Within 512s 512sdivide01sbit= 512bits

=64 bytes can be sent Every frame must be larger than 64 bytes

Data size must be larger than 46 bytes

39

Effect of CSMACD

Unpredicable when the frame can be received

Not fair Bandwidth utilization degrades if heavy

loading Not suitable for real-time applications

40

Properties of An Ethernet

Shared bus technology( broadcast) Lowest level hardware does not support

addressing Best-effort delivery mechanism No central authority to grant access Each transmission is limited in duration

41

Part 4

IEEE 8023

42

IEEE 802 Series

Fiber UTP wireless cable

80211 8023

8022 LLC (Logic Link Control)

SMTP FTPHTTP

TCP UDP

SNMP DNS

IP

Ethernet802128024 8025

bull8023 CDMACD

bull8024 Token-bus

bull8025 Token-ring

bull80211 Wireless LAN

bull80212 100VG-AnyLAN

43

IEEE 8023 Protocol

Ethernet is compatible to 8023 Length of bytes in LLC

Preamble SourceDestination Length Data from LLC FCS

Bytes 8 6 6 2 46-1500 4

64-1518 bytes

44

Flow Chart of IEEE 8023傳送訊框

組成訊框

線上有訊號

訊框過短( )衝撞

檢查碼正確

傳送訊框

發生衝撞

傳送完畢

jamming送出signal

i=i+1

i gt 16

計算延遲時間

等待延遲時間

傳送失敗傳送成功

Y es

No

No

No

Y es

Y es Y es

No

接收訊框

開始接收

接收完畢

位址辨識成功

尚有多餘位元

刪除訊框頭尾

長度錯誤對齊錯誤

Y es

No

No

No

Y es

Y es

Y es

接收成功訊框錯誤

長度欄位內容正確

No

Y es No

Y es

No

Page 19: 1 Introduction of Ethernet Metcalfe’s Ethernet sketch Also refer to nfhuang/chap04.htm

19

Part 2

Ethernet Frame

20

Ethernet Unreliable Connectionless

Connectionless No handshaking between sending and receiving NICs NIC Network Interface Card

Unreliable receiving NIC doesnrsquot send acks or nacks to sending NIC Stream of datagrams passed to network layer

can have gaps (missing datagrams) Gaps will be filled if application is using TCP Otherwise application will see gaps

Ethernetrsquos MAC protocol unslotted CSMACD

21

Ethernet frame (13)

Define the frame in MAC layer Preamble

7 bytes with pattern 10101010 followed by one byte with pattern 10101011

Used to synchronize receiver sender clock rates

Preamble SourceDestination TypeData fromupper layer

FCS

Bytes 8 6 6 2 46-1500 4

64-1518 bytes

22

Ethernet frame (23)

Source MAC address Source accepts the data from upper layer

encapsulates as a frame then sends it to destination

Destination MAC address If adapter receives frame with matching

destination address or with broadcast address (eg ARP packet) it passes data in frame to network layer protocol Otherwise adapter discards frame

LSB=0 physical MAC address LSB=1 multicast address All 1s in 6 bytes broadcast address

23

Ethernet frame (33)

Type Indicates higher layer protocol

0800H IP 0600H XNS (Xerox protocol suit) Mostly IP but others possible eg Novell IPX

AppleTalk Data

46-1500 bytes Frame Check Sequence (FCS)

Checked at receiver If error is detected the frame is dropped

Use 32-bits CRC to check address type and data

24

Manchester Encoding

Each bit has a transition Allows clocks in sending and receiving

nodes to synchronize to each other No need for a centralized global clock among

nodes

-0225V 07V

-1825V -07V

for coaxial cable

for UTP

25

Round-trip Propagation Delay

The time delay to send a signal on one round-trip In specification the maximum distance

between 2 hosts is 2800m Use 10Mbps Ethernet as an example

Round-trip propagation delay is about 4638 s

Finally round-trip propagation delay is set to be 512 s

26

Thick Ethernet Topology

Max distance =500m3+1000m2+300m=2800m

訊號傳遞速度為光速的 065 倍 2800m2divide(3108

065)=2872s Round trip delay 還包括電纜線傳遞延遲及元件延遲等

source httpwwwcsnthuedutw~nfhuangchap04htm

27

Part 3

Multiple Access in

Ethernet

28

Sending an Ethernet Frame

Broadcast If there are two computers send data at

the same time two frames will collide A collision occurs Receivers discards these frames

CSMACD( Carrier Sense Multiple Access Collision Detection ) is used

Best Effect

29

CSMACD

Carrier Sense 表示網路卡要對 carrier 進行監測判斷網路線上是否有資料的傳送

Multiple Access 指出這種機制的目的是要讓多個網路卡可以在同一個 carrier 上存取資料

Collision Detection 表示 collision 是會發生的必須靠 detection的機制來判斷是否有 collision

30

Ethernet CSMACD algorithm (12)

1 NIC receives datagram from network layer and creates frame

2 If NIC senses channel idle starts frame transmission

If NIC senses channel busy waits until channel idle and then transmits

3 If NIC transmits entire frame without detecting another transmission NIC is done with frame

31

Ethernet CSMACD algorithm (22)

4 If NIC detects another transmission while transmitting aborts and sends jam signal Jam Signal make sure all other transmitters

are aware of collision 48 bits

5 After aborting NIC enters exponential backoff NIC chooses K at random from 012hellip2m-1

after the m th collision

NIC waits K512 bit times returns to Step 2

32

No Collision Occurs

A電腦 B電腦

A電腦 B電腦A frame開始送出

A電腦 B電腦

B聽到網路上有資 料 必須等待

A collision確定沒有繼續送資料

time=0

time=512s

Ex 10BaseT

why

33

Collision Occurs

If host B sends it frame before getting Arsquos frame a collision occurs

Host A finds noise treat it as a collision

The worst case A finds noise after a

round-trip propagation delay time

A電腦 B電腦B frame開始送出

A電腦 B電腦A frame開始送出

A電腦 B電腦collision發生

A電腦 B電腦

A collision發現接著送出

jamming signal

B collision發現

34

How Long to Find Collision

Round-trip propagation delay is 512 s for 10Mbps Ethernet

Host A must listen at least 512 s and know whether a collision occurs or not

A電腦 B電腦B frame開始送出

A電腦 B電腦A 開始送出

frame

A電腦 B電腦collision發生

A電腦 B電腦

A collision發現接著送出

Jamming signal

B collisionB發現 也 Jamming siganl會送

35

CSMACD Random Time Delay (12)

Let two collided hosts retransmit frames at a different time Host generates a random time delay (r) r 0

1 2k-1 n the number of collisions( n16) k = min (n 10)

Retransmit the frame after r Exponential backoff algorithm

The random time delay is round-trip propagation delay r For 10BaseT 512 sr

36

CSMACD Random Time Delay (22)

Goal adapt retransmission attempts to estimated current load Heavy load random wait will be

longer

37

Examples of Binary Exponential Backoff Algorithm

First collision n=1 k=min(n10)=1 r 0 1 Probability=12 to send frame immediately Probability=12 to send frame after 512 s

Second collision n=2 k=min(n10)=2 r 0 1 2 3 Four cases 0s 512 s 512times2 s 512times3

s After ten collisions choose r from

01234hellip1023

38

Data Size Limitation

To avoid that any host occupies Ethernet too long the data size is smaller than 1500 bytes

If the size of a frame is too small adapters can not detect collision in time 10MHz 01sbit Within 512s 512sdivide01sbit= 512bits

=64 bytes can be sent Every frame must be larger than 64 bytes

Data size must be larger than 46 bytes

39

Effect of CSMACD

Unpredicable when the frame can be received

Not fair Bandwidth utilization degrades if heavy

loading Not suitable for real-time applications

40

Properties of An Ethernet

Shared bus technology( broadcast) Lowest level hardware does not support

addressing Best-effort delivery mechanism No central authority to grant access Each transmission is limited in duration

41

Part 4

IEEE 8023

42

IEEE 802 Series

Fiber UTP wireless cable

80211 8023

8022 LLC (Logic Link Control)

SMTP FTPHTTP

TCP UDP

SNMP DNS

IP

Ethernet802128024 8025

bull8023 CDMACD

bull8024 Token-bus

bull8025 Token-ring

bull80211 Wireless LAN

bull80212 100VG-AnyLAN

43

IEEE 8023 Protocol

Ethernet is compatible to 8023 Length of bytes in LLC

Preamble SourceDestination Length Data from LLC FCS

Bytes 8 6 6 2 46-1500 4

64-1518 bytes

44

Flow Chart of IEEE 8023傳送訊框

組成訊框

線上有訊號

訊框過短( )衝撞

檢查碼正確

傳送訊框

發生衝撞

傳送完畢

jamming送出signal

i=i+1

i gt 16

計算延遲時間

等待延遲時間

傳送失敗傳送成功

Y es

No

No

No

Y es

Y es Y es

No

接收訊框

開始接收

接收完畢

位址辨識成功

尚有多餘位元

刪除訊框頭尾

長度錯誤對齊錯誤

Y es

No

No

No

Y es

Y es

Y es

接收成功訊框錯誤

長度欄位內容正確

No

Y es No

Y es

No

Page 20: 1 Introduction of Ethernet Metcalfe’s Ethernet sketch Also refer to nfhuang/chap04.htm

20

Ethernet Unreliable Connectionless

Connectionless No handshaking between sending and receiving NICs NIC Network Interface Card

Unreliable receiving NIC doesnrsquot send acks or nacks to sending NIC Stream of datagrams passed to network layer

can have gaps (missing datagrams) Gaps will be filled if application is using TCP Otherwise application will see gaps

Ethernetrsquos MAC protocol unslotted CSMACD

21

Ethernet frame (13)

Define the frame in MAC layer Preamble

7 bytes with pattern 10101010 followed by one byte with pattern 10101011

Used to synchronize receiver sender clock rates

Preamble SourceDestination TypeData fromupper layer

FCS

Bytes 8 6 6 2 46-1500 4

64-1518 bytes

22

Ethernet frame (23)

Source MAC address Source accepts the data from upper layer

encapsulates as a frame then sends it to destination

Destination MAC address If adapter receives frame with matching

destination address or with broadcast address (eg ARP packet) it passes data in frame to network layer protocol Otherwise adapter discards frame

LSB=0 physical MAC address LSB=1 multicast address All 1s in 6 bytes broadcast address

23

Ethernet frame (33)

Type Indicates higher layer protocol

0800H IP 0600H XNS (Xerox protocol suit) Mostly IP but others possible eg Novell IPX

AppleTalk Data

46-1500 bytes Frame Check Sequence (FCS)

Checked at receiver If error is detected the frame is dropped

Use 32-bits CRC to check address type and data

24

Manchester Encoding

Each bit has a transition Allows clocks in sending and receiving

nodes to synchronize to each other No need for a centralized global clock among

nodes

-0225V 07V

-1825V -07V

for coaxial cable

for UTP

25

Round-trip Propagation Delay

The time delay to send a signal on one round-trip In specification the maximum distance

between 2 hosts is 2800m Use 10Mbps Ethernet as an example

Round-trip propagation delay is about 4638 s

Finally round-trip propagation delay is set to be 512 s

26

Thick Ethernet Topology

Max distance =500m3+1000m2+300m=2800m

訊號傳遞速度為光速的 065 倍 2800m2divide(3108

065)=2872s Round trip delay 還包括電纜線傳遞延遲及元件延遲等

source httpwwwcsnthuedutw~nfhuangchap04htm

27

Part 3

Multiple Access in

Ethernet

28

Sending an Ethernet Frame

Broadcast If there are two computers send data at

the same time two frames will collide A collision occurs Receivers discards these frames

CSMACD( Carrier Sense Multiple Access Collision Detection ) is used

Best Effect

29

CSMACD

Carrier Sense 表示網路卡要對 carrier 進行監測判斷網路線上是否有資料的傳送

Multiple Access 指出這種機制的目的是要讓多個網路卡可以在同一個 carrier 上存取資料

Collision Detection 表示 collision 是會發生的必須靠 detection的機制來判斷是否有 collision

30

Ethernet CSMACD algorithm (12)

1 NIC receives datagram from network layer and creates frame

2 If NIC senses channel idle starts frame transmission

If NIC senses channel busy waits until channel idle and then transmits

3 If NIC transmits entire frame without detecting another transmission NIC is done with frame

31

Ethernet CSMACD algorithm (22)

4 If NIC detects another transmission while transmitting aborts and sends jam signal Jam Signal make sure all other transmitters

are aware of collision 48 bits

5 After aborting NIC enters exponential backoff NIC chooses K at random from 012hellip2m-1

after the m th collision

NIC waits K512 bit times returns to Step 2

32

No Collision Occurs

A電腦 B電腦

A電腦 B電腦A frame開始送出

A電腦 B電腦

B聽到網路上有資 料 必須等待

A collision確定沒有繼續送資料

time=0

time=512s

Ex 10BaseT

why

33

Collision Occurs

If host B sends it frame before getting Arsquos frame a collision occurs

Host A finds noise treat it as a collision

The worst case A finds noise after a

round-trip propagation delay time

A電腦 B電腦B frame開始送出

A電腦 B電腦A frame開始送出

A電腦 B電腦collision發生

A電腦 B電腦

A collision發現接著送出

jamming signal

B collision發現

34

How Long to Find Collision

Round-trip propagation delay is 512 s for 10Mbps Ethernet

Host A must listen at least 512 s and know whether a collision occurs or not

A電腦 B電腦B frame開始送出

A電腦 B電腦A 開始送出

frame

A電腦 B電腦collision發生

A電腦 B電腦

A collision發現接著送出

Jamming signal

B collisionB發現 也 Jamming siganl會送

35

CSMACD Random Time Delay (12)

Let two collided hosts retransmit frames at a different time Host generates a random time delay (r) r 0

1 2k-1 n the number of collisions( n16) k = min (n 10)

Retransmit the frame after r Exponential backoff algorithm

The random time delay is round-trip propagation delay r For 10BaseT 512 sr

36

CSMACD Random Time Delay (22)

Goal adapt retransmission attempts to estimated current load Heavy load random wait will be

longer

37

Examples of Binary Exponential Backoff Algorithm

First collision n=1 k=min(n10)=1 r 0 1 Probability=12 to send frame immediately Probability=12 to send frame after 512 s

Second collision n=2 k=min(n10)=2 r 0 1 2 3 Four cases 0s 512 s 512times2 s 512times3

s After ten collisions choose r from

01234hellip1023

38

Data Size Limitation

To avoid that any host occupies Ethernet too long the data size is smaller than 1500 bytes

If the size of a frame is too small adapters can not detect collision in time 10MHz 01sbit Within 512s 512sdivide01sbit= 512bits

=64 bytes can be sent Every frame must be larger than 64 bytes

Data size must be larger than 46 bytes

39

Effect of CSMACD

Unpredicable when the frame can be received

Not fair Bandwidth utilization degrades if heavy

loading Not suitable for real-time applications

40

Properties of An Ethernet

Shared bus technology( broadcast) Lowest level hardware does not support

addressing Best-effort delivery mechanism No central authority to grant access Each transmission is limited in duration

41

Part 4

IEEE 8023

42

IEEE 802 Series

Fiber UTP wireless cable

80211 8023

8022 LLC (Logic Link Control)

SMTP FTPHTTP

TCP UDP

SNMP DNS

IP

Ethernet802128024 8025

bull8023 CDMACD

bull8024 Token-bus

bull8025 Token-ring

bull80211 Wireless LAN

bull80212 100VG-AnyLAN

43

IEEE 8023 Protocol

Ethernet is compatible to 8023 Length of bytes in LLC

Preamble SourceDestination Length Data from LLC FCS

Bytes 8 6 6 2 46-1500 4

64-1518 bytes

44

Flow Chart of IEEE 8023傳送訊框

組成訊框

線上有訊號

訊框過短( )衝撞

檢查碼正確

傳送訊框

發生衝撞

傳送完畢

jamming送出signal

i=i+1

i gt 16

計算延遲時間

等待延遲時間

傳送失敗傳送成功

Y es

No

No

No

Y es

Y es Y es

No

接收訊框

開始接收

接收完畢

位址辨識成功

尚有多餘位元

刪除訊框頭尾

長度錯誤對齊錯誤

Y es

No

No

No

Y es

Y es

Y es

接收成功訊框錯誤

長度欄位內容正確

No

Y es No

Y es

No

Page 21: 1 Introduction of Ethernet Metcalfe’s Ethernet sketch Also refer to nfhuang/chap04.htm

21

Ethernet frame (13)

Define the frame in MAC layer Preamble

7 bytes with pattern 10101010 followed by one byte with pattern 10101011

Used to synchronize receiver sender clock rates

Preamble SourceDestination TypeData fromupper layer

FCS

Bytes 8 6 6 2 46-1500 4

64-1518 bytes

22

Ethernet frame (23)

Source MAC address Source accepts the data from upper layer

encapsulates as a frame then sends it to destination

Destination MAC address If adapter receives frame with matching

destination address or with broadcast address (eg ARP packet) it passes data in frame to network layer protocol Otherwise adapter discards frame

LSB=0 physical MAC address LSB=1 multicast address All 1s in 6 bytes broadcast address

23

Ethernet frame (33)

Type Indicates higher layer protocol

0800H IP 0600H XNS (Xerox protocol suit) Mostly IP but others possible eg Novell IPX

AppleTalk Data

46-1500 bytes Frame Check Sequence (FCS)

Checked at receiver If error is detected the frame is dropped

Use 32-bits CRC to check address type and data

24

Manchester Encoding

Each bit has a transition Allows clocks in sending and receiving

nodes to synchronize to each other No need for a centralized global clock among

nodes

-0225V 07V

-1825V -07V

for coaxial cable

for UTP

25

Round-trip Propagation Delay

The time delay to send a signal on one round-trip In specification the maximum distance

between 2 hosts is 2800m Use 10Mbps Ethernet as an example

Round-trip propagation delay is about 4638 s

Finally round-trip propagation delay is set to be 512 s

26

Thick Ethernet Topology

Max distance =500m3+1000m2+300m=2800m

訊號傳遞速度為光速的 065 倍 2800m2divide(3108

065)=2872s Round trip delay 還包括電纜線傳遞延遲及元件延遲等

source httpwwwcsnthuedutw~nfhuangchap04htm

27

Part 3

Multiple Access in

Ethernet

28

Sending an Ethernet Frame

Broadcast If there are two computers send data at

the same time two frames will collide A collision occurs Receivers discards these frames

CSMACD( Carrier Sense Multiple Access Collision Detection ) is used

Best Effect

29

CSMACD

Carrier Sense 表示網路卡要對 carrier 進行監測判斷網路線上是否有資料的傳送

Multiple Access 指出這種機制的目的是要讓多個網路卡可以在同一個 carrier 上存取資料

Collision Detection 表示 collision 是會發生的必須靠 detection的機制來判斷是否有 collision

30

Ethernet CSMACD algorithm (12)

1 NIC receives datagram from network layer and creates frame

2 If NIC senses channel idle starts frame transmission

If NIC senses channel busy waits until channel idle and then transmits

3 If NIC transmits entire frame without detecting another transmission NIC is done with frame

31

Ethernet CSMACD algorithm (22)

4 If NIC detects another transmission while transmitting aborts and sends jam signal Jam Signal make sure all other transmitters

are aware of collision 48 bits

5 After aborting NIC enters exponential backoff NIC chooses K at random from 012hellip2m-1

after the m th collision

NIC waits K512 bit times returns to Step 2

32

No Collision Occurs

A電腦 B電腦

A電腦 B電腦A frame開始送出

A電腦 B電腦

B聽到網路上有資 料 必須等待

A collision確定沒有繼續送資料

time=0

time=512s

Ex 10BaseT

why

33

Collision Occurs

If host B sends it frame before getting Arsquos frame a collision occurs

Host A finds noise treat it as a collision

The worst case A finds noise after a

round-trip propagation delay time

A電腦 B電腦B frame開始送出

A電腦 B電腦A frame開始送出

A電腦 B電腦collision發生

A電腦 B電腦

A collision發現接著送出

jamming signal

B collision發現

34

How Long to Find Collision

Round-trip propagation delay is 512 s for 10Mbps Ethernet

Host A must listen at least 512 s and know whether a collision occurs or not

A電腦 B電腦B frame開始送出

A電腦 B電腦A 開始送出

frame

A電腦 B電腦collision發生

A電腦 B電腦

A collision發現接著送出

Jamming signal

B collisionB發現 也 Jamming siganl會送

35

CSMACD Random Time Delay (12)

Let two collided hosts retransmit frames at a different time Host generates a random time delay (r) r 0

1 2k-1 n the number of collisions( n16) k = min (n 10)

Retransmit the frame after r Exponential backoff algorithm

The random time delay is round-trip propagation delay r For 10BaseT 512 sr

36

CSMACD Random Time Delay (22)

Goal adapt retransmission attempts to estimated current load Heavy load random wait will be

longer

37

Examples of Binary Exponential Backoff Algorithm

First collision n=1 k=min(n10)=1 r 0 1 Probability=12 to send frame immediately Probability=12 to send frame after 512 s

Second collision n=2 k=min(n10)=2 r 0 1 2 3 Four cases 0s 512 s 512times2 s 512times3

s After ten collisions choose r from

01234hellip1023

38

Data Size Limitation

To avoid that any host occupies Ethernet too long the data size is smaller than 1500 bytes

If the size of a frame is too small adapters can not detect collision in time 10MHz 01sbit Within 512s 512sdivide01sbit= 512bits

=64 bytes can be sent Every frame must be larger than 64 bytes

Data size must be larger than 46 bytes

39

Effect of CSMACD

Unpredicable when the frame can be received

Not fair Bandwidth utilization degrades if heavy

loading Not suitable for real-time applications

40

Properties of An Ethernet

Shared bus technology( broadcast) Lowest level hardware does not support

addressing Best-effort delivery mechanism No central authority to grant access Each transmission is limited in duration

41

Part 4

IEEE 8023

42

IEEE 802 Series

Fiber UTP wireless cable

80211 8023

8022 LLC (Logic Link Control)

SMTP FTPHTTP

TCP UDP

SNMP DNS

IP

Ethernet802128024 8025

bull8023 CDMACD

bull8024 Token-bus

bull8025 Token-ring

bull80211 Wireless LAN

bull80212 100VG-AnyLAN

43

IEEE 8023 Protocol

Ethernet is compatible to 8023 Length of bytes in LLC

Preamble SourceDestination Length Data from LLC FCS

Bytes 8 6 6 2 46-1500 4

64-1518 bytes

44

Flow Chart of IEEE 8023傳送訊框

組成訊框

線上有訊號

訊框過短( )衝撞

檢查碼正確

傳送訊框

發生衝撞

傳送完畢

jamming送出signal

i=i+1

i gt 16

計算延遲時間

等待延遲時間

傳送失敗傳送成功

Y es

No

No

No

Y es

Y es Y es

No

接收訊框

開始接收

接收完畢

位址辨識成功

尚有多餘位元

刪除訊框頭尾

長度錯誤對齊錯誤

Y es

No

No

No

Y es

Y es

Y es

接收成功訊框錯誤

長度欄位內容正確

No

Y es No

Y es

No

Page 22: 1 Introduction of Ethernet Metcalfe’s Ethernet sketch Also refer to nfhuang/chap04.htm

22

Ethernet frame (23)

Source MAC address Source accepts the data from upper layer

encapsulates as a frame then sends it to destination

Destination MAC address If adapter receives frame with matching

destination address or with broadcast address (eg ARP packet) it passes data in frame to network layer protocol Otherwise adapter discards frame

LSB=0 physical MAC address LSB=1 multicast address All 1s in 6 bytes broadcast address

23

Ethernet frame (33)

Type Indicates higher layer protocol

0800H IP 0600H XNS (Xerox protocol suit) Mostly IP but others possible eg Novell IPX

AppleTalk Data

46-1500 bytes Frame Check Sequence (FCS)

Checked at receiver If error is detected the frame is dropped

Use 32-bits CRC to check address type and data

24

Manchester Encoding

Each bit has a transition Allows clocks in sending and receiving

nodes to synchronize to each other No need for a centralized global clock among

nodes

-0225V 07V

-1825V -07V

for coaxial cable

for UTP

25

Round-trip Propagation Delay

The time delay to send a signal on one round-trip In specification the maximum distance

between 2 hosts is 2800m Use 10Mbps Ethernet as an example

Round-trip propagation delay is about 4638 s

Finally round-trip propagation delay is set to be 512 s

26

Thick Ethernet Topology

Max distance =500m3+1000m2+300m=2800m

訊號傳遞速度為光速的 065 倍 2800m2divide(3108

065)=2872s Round trip delay 還包括電纜線傳遞延遲及元件延遲等

source httpwwwcsnthuedutw~nfhuangchap04htm

27

Part 3

Multiple Access in

Ethernet

28

Sending an Ethernet Frame

Broadcast If there are two computers send data at

the same time two frames will collide A collision occurs Receivers discards these frames

CSMACD( Carrier Sense Multiple Access Collision Detection ) is used

Best Effect

29

CSMACD

Carrier Sense 表示網路卡要對 carrier 進行監測判斷網路線上是否有資料的傳送

Multiple Access 指出這種機制的目的是要讓多個網路卡可以在同一個 carrier 上存取資料

Collision Detection 表示 collision 是會發生的必須靠 detection的機制來判斷是否有 collision

30

Ethernet CSMACD algorithm (12)

1 NIC receives datagram from network layer and creates frame

2 If NIC senses channel idle starts frame transmission

If NIC senses channel busy waits until channel idle and then transmits

3 If NIC transmits entire frame without detecting another transmission NIC is done with frame

31

Ethernet CSMACD algorithm (22)

4 If NIC detects another transmission while transmitting aborts and sends jam signal Jam Signal make sure all other transmitters

are aware of collision 48 bits

5 After aborting NIC enters exponential backoff NIC chooses K at random from 012hellip2m-1

after the m th collision

NIC waits K512 bit times returns to Step 2

32

No Collision Occurs

A電腦 B電腦

A電腦 B電腦A frame開始送出

A電腦 B電腦

B聽到網路上有資 料 必須等待

A collision確定沒有繼續送資料

time=0

time=512s

Ex 10BaseT

why

33

Collision Occurs

If host B sends it frame before getting Arsquos frame a collision occurs

Host A finds noise treat it as a collision

The worst case A finds noise after a

round-trip propagation delay time

A電腦 B電腦B frame開始送出

A電腦 B電腦A frame開始送出

A電腦 B電腦collision發生

A電腦 B電腦

A collision發現接著送出

jamming signal

B collision發現

34

How Long to Find Collision

Round-trip propagation delay is 512 s for 10Mbps Ethernet

Host A must listen at least 512 s and know whether a collision occurs or not

A電腦 B電腦B frame開始送出

A電腦 B電腦A 開始送出

frame

A電腦 B電腦collision發生

A電腦 B電腦

A collision發現接著送出

Jamming signal

B collisionB發現 也 Jamming siganl會送

35

CSMACD Random Time Delay (12)

Let two collided hosts retransmit frames at a different time Host generates a random time delay (r) r 0

1 2k-1 n the number of collisions( n16) k = min (n 10)

Retransmit the frame after r Exponential backoff algorithm

The random time delay is round-trip propagation delay r For 10BaseT 512 sr

36

CSMACD Random Time Delay (22)

Goal adapt retransmission attempts to estimated current load Heavy load random wait will be

longer

37

Examples of Binary Exponential Backoff Algorithm

First collision n=1 k=min(n10)=1 r 0 1 Probability=12 to send frame immediately Probability=12 to send frame after 512 s

Second collision n=2 k=min(n10)=2 r 0 1 2 3 Four cases 0s 512 s 512times2 s 512times3

s After ten collisions choose r from

01234hellip1023

38

Data Size Limitation

To avoid that any host occupies Ethernet too long the data size is smaller than 1500 bytes

If the size of a frame is too small adapters can not detect collision in time 10MHz 01sbit Within 512s 512sdivide01sbit= 512bits

=64 bytes can be sent Every frame must be larger than 64 bytes

Data size must be larger than 46 bytes

39

Effect of CSMACD

Unpredicable when the frame can be received

Not fair Bandwidth utilization degrades if heavy

loading Not suitable for real-time applications

40

Properties of An Ethernet

Shared bus technology( broadcast) Lowest level hardware does not support

addressing Best-effort delivery mechanism No central authority to grant access Each transmission is limited in duration

41

Part 4

IEEE 8023

42

IEEE 802 Series

Fiber UTP wireless cable

80211 8023

8022 LLC (Logic Link Control)

SMTP FTPHTTP

TCP UDP

SNMP DNS

IP

Ethernet802128024 8025

bull8023 CDMACD

bull8024 Token-bus

bull8025 Token-ring

bull80211 Wireless LAN

bull80212 100VG-AnyLAN

43

IEEE 8023 Protocol

Ethernet is compatible to 8023 Length of bytes in LLC

Preamble SourceDestination Length Data from LLC FCS

Bytes 8 6 6 2 46-1500 4

64-1518 bytes

44

Flow Chart of IEEE 8023傳送訊框

組成訊框

線上有訊號

訊框過短( )衝撞

檢查碼正確

傳送訊框

發生衝撞

傳送完畢

jamming送出signal

i=i+1

i gt 16

計算延遲時間

等待延遲時間

傳送失敗傳送成功

Y es

No

No

No

Y es

Y es Y es

No

接收訊框

開始接收

接收完畢

位址辨識成功

尚有多餘位元

刪除訊框頭尾

長度錯誤對齊錯誤

Y es

No

No

No

Y es

Y es

Y es

接收成功訊框錯誤

長度欄位內容正確

No

Y es No

Y es

No

Page 23: 1 Introduction of Ethernet Metcalfe’s Ethernet sketch Also refer to nfhuang/chap04.htm

23

Ethernet frame (33)

Type Indicates higher layer protocol

0800H IP 0600H XNS (Xerox protocol suit) Mostly IP but others possible eg Novell IPX

AppleTalk Data

46-1500 bytes Frame Check Sequence (FCS)

Checked at receiver If error is detected the frame is dropped

Use 32-bits CRC to check address type and data

24

Manchester Encoding

Each bit has a transition Allows clocks in sending and receiving

nodes to synchronize to each other No need for a centralized global clock among

nodes

-0225V 07V

-1825V -07V

for coaxial cable

for UTP

25

Round-trip Propagation Delay

The time delay to send a signal on one round-trip In specification the maximum distance

between 2 hosts is 2800m Use 10Mbps Ethernet as an example

Round-trip propagation delay is about 4638 s

Finally round-trip propagation delay is set to be 512 s

26

Thick Ethernet Topology

Max distance =500m3+1000m2+300m=2800m

訊號傳遞速度為光速的 065 倍 2800m2divide(3108

065)=2872s Round trip delay 還包括電纜線傳遞延遲及元件延遲等

source httpwwwcsnthuedutw~nfhuangchap04htm

27

Part 3

Multiple Access in

Ethernet

28

Sending an Ethernet Frame

Broadcast If there are two computers send data at

the same time two frames will collide A collision occurs Receivers discards these frames

CSMACD( Carrier Sense Multiple Access Collision Detection ) is used

Best Effect

29

CSMACD

Carrier Sense 表示網路卡要對 carrier 進行監測判斷網路線上是否有資料的傳送

Multiple Access 指出這種機制的目的是要讓多個網路卡可以在同一個 carrier 上存取資料

Collision Detection 表示 collision 是會發生的必須靠 detection的機制來判斷是否有 collision

30

Ethernet CSMACD algorithm (12)

1 NIC receives datagram from network layer and creates frame

2 If NIC senses channel idle starts frame transmission

If NIC senses channel busy waits until channel idle and then transmits

3 If NIC transmits entire frame without detecting another transmission NIC is done with frame

31

Ethernet CSMACD algorithm (22)

4 If NIC detects another transmission while transmitting aborts and sends jam signal Jam Signal make sure all other transmitters

are aware of collision 48 bits

5 After aborting NIC enters exponential backoff NIC chooses K at random from 012hellip2m-1

after the m th collision

NIC waits K512 bit times returns to Step 2

32

No Collision Occurs

A電腦 B電腦

A電腦 B電腦A frame開始送出

A電腦 B電腦

B聽到網路上有資 料 必須等待

A collision確定沒有繼續送資料

time=0

time=512s

Ex 10BaseT

why

33

Collision Occurs

If host B sends it frame before getting Arsquos frame a collision occurs

Host A finds noise treat it as a collision

The worst case A finds noise after a

round-trip propagation delay time

A電腦 B電腦B frame開始送出

A電腦 B電腦A frame開始送出

A電腦 B電腦collision發生

A電腦 B電腦

A collision發現接著送出

jamming signal

B collision發現

34

How Long to Find Collision

Round-trip propagation delay is 512 s for 10Mbps Ethernet

Host A must listen at least 512 s and know whether a collision occurs or not

A電腦 B電腦B frame開始送出

A電腦 B電腦A 開始送出

frame

A電腦 B電腦collision發生

A電腦 B電腦

A collision發現接著送出

Jamming signal

B collisionB發現 也 Jamming siganl會送

35

CSMACD Random Time Delay (12)

Let two collided hosts retransmit frames at a different time Host generates a random time delay (r) r 0

1 2k-1 n the number of collisions( n16) k = min (n 10)

Retransmit the frame after r Exponential backoff algorithm

The random time delay is round-trip propagation delay r For 10BaseT 512 sr

36

CSMACD Random Time Delay (22)

Goal adapt retransmission attempts to estimated current load Heavy load random wait will be

longer

37

Examples of Binary Exponential Backoff Algorithm

First collision n=1 k=min(n10)=1 r 0 1 Probability=12 to send frame immediately Probability=12 to send frame after 512 s

Second collision n=2 k=min(n10)=2 r 0 1 2 3 Four cases 0s 512 s 512times2 s 512times3

s After ten collisions choose r from

01234hellip1023

38

Data Size Limitation

To avoid that any host occupies Ethernet too long the data size is smaller than 1500 bytes

If the size of a frame is too small adapters can not detect collision in time 10MHz 01sbit Within 512s 512sdivide01sbit= 512bits

=64 bytes can be sent Every frame must be larger than 64 bytes

Data size must be larger than 46 bytes

39

Effect of CSMACD

Unpredicable when the frame can be received

Not fair Bandwidth utilization degrades if heavy

loading Not suitable for real-time applications

40

Properties of An Ethernet

Shared bus technology( broadcast) Lowest level hardware does not support

addressing Best-effort delivery mechanism No central authority to grant access Each transmission is limited in duration

41

Part 4

IEEE 8023

42

IEEE 802 Series

Fiber UTP wireless cable

80211 8023

8022 LLC (Logic Link Control)

SMTP FTPHTTP

TCP UDP

SNMP DNS

IP

Ethernet802128024 8025

bull8023 CDMACD

bull8024 Token-bus

bull8025 Token-ring

bull80211 Wireless LAN

bull80212 100VG-AnyLAN

43

IEEE 8023 Protocol

Ethernet is compatible to 8023 Length of bytes in LLC

Preamble SourceDestination Length Data from LLC FCS

Bytes 8 6 6 2 46-1500 4

64-1518 bytes

44

Flow Chart of IEEE 8023傳送訊框

組成訊框

線上有訊號

訊框過短( )衝撞

檢查碼正確

傳送訊框

發生衝撞

傳送完畢

jamming送出signal

i=i+1

i gt 16

計算延遲時間

等待延遲時間

傳送失敗傳送成功

Y es

No

No

No

Y es

Y es Y es

No

接收訊框

開始接收

接收完畢

位址辨識成功

尚有多餘位元

刪除訊框頭尾

長度錯誤對齊錯誤

Y es

No

No

No

Y es

Y es

Y es

接收成功訊框錯誤

長度欄位內容正確

No

Y es No

Y es

No

Page 24: 1 Introduction of Ethernet Metcalfe’s Ethernet sketch Also refer to nfhuang/chap04.htm

24

Manchester Encoding

Each bit has a transition Allows clocks in sending and receiving

nodes to synchronize to each other No need for a centralized global clock among

nodes

-0225V 07V

-1825V -07V

for coaxial cable

for UTP

25

Round-trip Propagation Delay

The time delay to send a signal on one round-trip In specification the maximum distance

between 2 hosts is 2800m Use 10Mbps Ethernet as an example

Round-trip propagation delay is about 4638 s

Finally round-trip propagation delay is set to be 512 s

26

Thick Ethernet Topology

Max distance =500m3+1000m2+300m=2800m

訊號傳遞速度為光速的 065 倍 2800m2divide(3108

065)=2872s Round trip delay 還包括電纜線傳遞延遲及元件延遲等

source httpwwwcsnthuedutw~nfhuangchap04htm

27

Part 3

Multiple Access in

Ethernet

28

Sending an Ethernet Frame

Broadcast If there are two computers send data at

the same time two frames will collide A collision occurs Receivers discards these frames

CSMACD( Carrier Sense Multiple Access Collision Detection ) is used

Best Effect

29

CSMACD

Carrier Sense 表示網路卡要對 carrier 進行監測判斷網路線上是否有資料的傳送

Multiple Access 指出這種機制的目的是要讓多個網路卡可以在同一個 carrier 上存取資料

Collision Detection 表示 collision 是會發生的必須靠 detection的機制來判斷是否有 collision

30

Ethernet CSMACD algorithm (12)

1 NIC receives datagram from network layer and creates frame

2 If NIC senses channel idle starts frame transmission

If NIC senses channel busy waits until channel idle and then transmits

3 If NIC transmits entire frame without detecting another transmission NIC is done with frame

31

Ethernet CSMACD algorithm (22)

4 If NIC detects another transmission while transmitting aborts and sends jam signal Jam Signal make sure all other transmitters

are aware of collision 48 bits

5 After aborting NIC enters exponential backoff NIC chooses K at random from 012hellip2m-1

after the m th collision

NIC waits K512 bit times returns to Step 2

32

No Collision Occurs

A電腦 B電腦

A電腦 B電腦A frame開始送出

A電腦 B電腦

B聽到網路上有資 料 必須等待

A collision確定沒有繼續送資料

time=0

time=512s

Ex 10BaseT

why

33

Collision Occurs

If host B sends it frame before getting Arsquos frame a collision occurs

Host A finds noise treat it as a collision

The worst case A finds noise after a

round-trip propagation delay time

A電腦 B電腦B frame開始送出

A電腦 B電腦A frame開始送出

A電腦 B電腦collision發生

A電腦 B電腦

A collision發現接著送出

jamming signal

B collision發現

34

How Long to Find Collision

Round-trip propagation delay is 512 s for 10Mbps Ethernet

Host A must listen at least 512 s and know whether a collision occurs or not

A電腦 B電腦B frame開始送出

A電腦 B電腦A 開始送出

frame

A電腦 B電腦collision發生

A電腦 B電腦

A collision發現接著送出

Jamming signal

B collisionB發現 也 Jamming siganl會送

35

CSMACD Random Time Delay (12)

Let two collided hosts retransmit frames at a different time Host generates a random time delay (r) r 0

1 2k-1 n the number of collisions( n16) k = min (n 10)

Retransmit the frame after r Exponential backoff algorithm

The random time delay is round-trip propagation delay r For 10BaseT 512 sr

36

CSMACD Random Time Delay (22)

Goal adapt retransmission attempts to estimated current load Heavy load random wait will be

longer

37

Examples of Binary Exponential Backoff Algorithm

First collision n=1 k=min(n10)=1 r 0 1 Probability=12 to send frame immediately Probability=12 to send frame after 512 s

Second collision n=2 k=min(n10)=2 r 0 1 2 3 Four cases 0s 512 s 512times2 s 512times3

s After ten collisions choose r from

01234hellip1023

38

Data Size Limitation

To avoid that any host occupies Ethernet too long the data size is smaller than 1500 bytes

If the size of a frame is too small adapters can not detect collision in time 10MHz 01sbit Within 512s 512sdivide01sbit= 512bits

=64 bytes can be sent Every frame must be larger than 64 bytes

Data size must be larger than 46 bytes

39

Effect of CSMACD

Unpredicable when the frame can be received

Not fair Bandwidth utilization degrades if heavy

loading Not suitable for real-time applications

40

Properties of An Ethernet

Shared bus technology( broadcast) Lowest level hardware does not support

addressing Best-effort delivery mechanism No central authority to grant access Each transmission is limited in duration

41

Part 4

IEEE 8023

42

IEEE 802 Series

Fiber UTP wireless cable

80211 8023

8022 LLC (Logic Link Control)

SMTP FTPHTTP

TCP UDP

SNMP DNS

IP

Ethernet802128024 8025

bull8023 CDMACD

bull8024 Token-bus

bull8025 Token-ring

bull80211 Wireless LAN

bull80212 100VG-AnyLAN

43

IEEE 8023 Protocol

Ethernet is compatible to 8023 Length of bytes in LLC

Preamble SourceDestination Length Data from LLC FCS

Bytes 8 6 6 2 46-1500 4

64-1518 bytes

44

Flow Chart of IEEE 8023傳送訊框

組成訊框

線上有訊號

訊框過短( )衝撞

檢查碼正確

傳送訊框

發生衝撞

傳送完畢

jamming送出signal

i=i+1

i gt 16

計算延遲時間

等待延遲時間

傳送失敗傳送成功

Y es

No

No

No

Y es

Y es Y es

No

接收訊框

開始接收

接收完畢

位址辨識成功

尚有多餘位元

刪除訊框頭尾

長度錯誤對齊錯誤

Y es

No

No

No

Y es

Y es

Y es

接收成功訊框錯誤

長度欄位內容正確

No

Y es No

Y es

No

Page 25: 1 Introduction of Ethernet Metcalfe’s Ethernet sketch Also refer to nfhuang/chap04.htm

25

Round-trip Propagation Delay

The time delay to send a signal on one round-trip In specification the maximum distance

between 2 hosts is 2800m Use 10Mbps Ethernet as an example

Round-trip propagation delay is about 4638 s

Finally round-trip propagation delay is set to be 512 s

26

Thick Ethernet Topology

Max distance =500m3+1000m2+300m=2800m

訊號傳遞速度為光速的 065 倍 2800m2divide(3108

065)=2872s Round trip delay 還包括電纜線傳遞延遲及元件延遲等

source httpwwwcsnthuedutw~nfhuangchap04htm

27

Part 3

Multiple Access in

Ethernet

28

Sending an Ethernet Frame

Broadcast If there are two computers send data at

the same time two frames will collide A collision occurs Receivers discards these frames

CSMACD( Carrier Sense Multiple Access Collision Detection ) is used

Best Effect

29

CSMACD

Carrier Sense 表示網路卡要對 carrier 進行監測判斷網路線上是否有資料的傳送

Multiple Access 指出這種機制的目的是要讓多個網路卡可以在同一個 carrier 上存取資料

Collision Detection 表示 collision 是會發生的必須靠 detection的機制來判斷是否有 collision

30

Ethernet CSMACD algorithm (12)

1 NIC receives datagram from network layer and creates frame

2 If NIC senses channel idle starts frame transmission

If NIC senses channel busy waits until channel idle and then transmits

3 If NIC transmits entire frame without detecting another transmission NIC is done with frame

31

Ethernet CSMACD algorithm (22)

4 If NIC detects another transmission while transmitting aborts and sends jam signal Jam Signal make sure all other transmitters

are aware of collision 48 bits

5 After aborting NIC enters exponential backoff NIC chooses K at random from 012hellip2m-1

after the m th collision

NIC waits K512 bit times returns to Step 2

32

No Collision Occurs

A電腦 B電腦

A電腦 B電腦A frame開始送出

A電腦 B電腦

B聽到網路上有資 料 必須等待

A collision確定沒有繼續送資料

time=0

time=512s

Ex 10BaseT

why

33

Collision Occurs

If host B sends it frame before getting Arsquos frame a collision occurs

Host A finds noise treat it as a collision

The worst case A finds noise after a

round-trip propagation delay time

A電腦 B電腦B frame開始送出

A電腦 B電腦A frame開始送出

A電腦 B電腦collision發生

A電腦 B電腦

A collision發現接著送出

jamming signal

B collision發現

34

How Long to Find Collision

Round-trip propagation delay is 512 s for 10Mbps Ethernet

Host A must listen at least 512 s and know whether a collision occurs or not

A電腦 B電腦B frame開始送出

A電腦 B電腦A 開始送出

frame

A電腦 B電腦collision發生

A電腦 B電腦

A collision發現接著送出

Jamming signal

B collisionB發現 也 Jamming siganl會送

35

CSMACD Random Time Delay (12)

Let two collided hosts retransmit frames at a different time Host generates a random time delay (r) r 0

1 2k-1 n the number of collisions( n16) k = min (n 10)

Retransmit the frame after r Exponential backoff algorithm

The random time delay is round-trip propagation delay r For 10BaseT 512 sr

36

CSMACD Random Time Delay (22)

Goal adapt retransmission attempts to estimated current load Heavy load random wait will be

longer

37

Examples of Binary Exponential Backoff Algorithm

First collision n=1 k=min(n10)=1 r 0 1 Probability=12 to send frame immediately Probability=12 to send frame after 512 s

Second collision n=2 k=min(n10)=2 r 0 1 2 3 Four cases 0s 512 s 512times2 s 512times3

s After ten collisions choose r from

01234hellip1023

38

Data Size Limitation

To avoid that any host occupies Ethernet too long the data size is smaller than 1500 bytes

If the size of a frame is too small adapters can not detect collision in time 10MHz 01sbit Within 512s 512sdivide01sbit= 512bits

=64 bytes can be sent Every frame must be larger than 64 bytes

Data size must be larger than 46 bytes

39

Effect of CSMACD

Unpredicable when the frame can be received

Not fair Bandwidth utilization degrades if heavy

loading Not suitable for real-time applications

40

Properties of An Ethernet

Shared bus technology( broadcast) Lowest level hardware does not support

addressing Best-effort delivery mechanism No central authority to grant access Each transmission is limited in duration

41

Part 4

IEEE 8023

42

IEEE 802 Series

Fiber UTP wireless cable

80211 8023

8022 LLC (Logic Link Control)

SMTP FTPHTTP

TCP UDP

SNMP DNS

IP

Ethernet802128024 8025

bull8023 CDMACD

bull8024 Token-bus

bull8025 Token-ring

bull80211 Wireless LAN

bull80212 100VG-AnyLAN

43

IEEE 8023 Protocol

Ethernet is compatible to 8023 Length of bytes in LLC

Preamble SourceDestination Length Data from LLC FCS

Bytes 8 6 6 2 46-1500 4

64-1518 bytes

44

Flow Chart of IEEE 8023傳送訊框

組成訊框

線上有訊號

訊框過短( )衝撞

檢查碼正確

傳送訊框

發生衝撞

傳送完畢

jamming送出signal

i=i+1

i gt 16

計算延遲時間

等待延遲時間

傳送失敗傳送成功

Y es

No

No

No

Y es

Y es Y es

No

接收訊框

開始接收

接收完畢

位址辨識成功

尚有多餘位元

刪除訊框頭尾

長度錯誤對齊錯誤

Y es

No

No

No

Y es

Y es

Y es

接收成功訊框錯誤

長度欄位內容正確

No

Y es No

Y es

No

Page 26: 1 Introduction of Ethernet Metcalfe’s Ethernet sketch Also refer to nfhuang/chap04.htm

26

Thick Ethernet Topology

Max distance =500m3+1000m2+300m=2800m

訊號傳遞速度為光速的 065 倍 2800m2divide(3108

065)=2872s Round trip delay 還包括電纜線傳遞延遲及元件延遲等

source httpwwwcsnthuedutw~nfhuangchap04htm

27

Part 3

Multiple Access in

Ethernet

28

Sending an Ethernet Frame

Broadcast If there are two computers send data at

the same time two frames will collide A collision occurs Receivers discards these frames

CSMACD( Carrier Sense Multiple Access Collision Detection ) is used

Best Effect

29

CSMACD

Carrier Sense 表示網路卡要對 carrier 進行監測判斷網路線上是否有資料的傳送

Multiple Access 指出這種機制的目的是要讓多個網路卡可以在同一個 carrier 上存取資料

Collision Detection 表示 collision 是會發生的必須靠 detection的機制來判斷是否有 collision

30

Ethernet CSMACD algorithm (12)

1 NIC receives datagram from network layer and creates frame

2 If NIC senses channel idle starts frame transmission

If NIC senses channel busy waits until channel idle and then transmits

3 If NIC transmits entire frame without detecting another transmission NIC is done with frame

31

Ethernet CSMACD algorithm (22)

4 If NIC detects another transmission while transmitting aborts and sends jam signal Jam Signal make sure all other transmitters

are aware of collision 48 bits

5 After aborting NIC enters exponential backoff NIC chooses K at random from 012hellip2m-1

after the m th collision

NIC waits K512 bit times returns to Step 2

32

No Collision Occurs

A電腦 B電腦

A電腦 B電腦A frame開始送出

A電腦 B電腦

B聽到網路上有資 料 必須等待

A collision確定沒有繼續送資料

time=0

time=512s

Ex 10BaseT

why

33

Collision Occurs

If host B sends it frame before getting Arsquos frame a collision occurs

Host A finds noise treat it as a collision

The worst case A finds noise after a

round-trip propagation delay time

A電腦 B電腦B frame開始送出

A電腦 B電腦A frame開始送出

A電腦 B電腦collision發生

A電腦 B電腦

A collision發現接著送出

jamming signal

B collision發現

34

How Long to Find Collision

Round-trip propagation delay is 512 s for 10Mbps Ethernet

Host A must listen at least 512 s and know whether a collision occurs or not

A電腦 B電腦B frame開始送出

A電腦 B電腦A 開始送出

frame

A電腦 B電腦collision發生

A電腦 B電腦

A collision發現接著送出

Jamming signal

B collisionB發現 也 Jamming siganl會送

35

CSMACD Random Time Delay (12)

Let two collided hosts retransmit frames at a different time Host generates a random time delay (r) r 0

1 2k-1 n the number of collisions( n16) k = min (n 10)

Retransmit the frame after r Exponential backoff algorithm

The random time delay is round-trip propagation delay r For 10BaseT 512 sr

36

CSMACD Random Time Delay (22)

Goal adapt retransmission attempts to estimated current load Heavy load random wait will be

longer

37

Examples of Binary Exponential Backoff Algorithm

First collision n=1 k=min(n10)=1 r 0 1 Probability=12 to send frame immediately Probability=12 to send frame after 512 s

Second collision n=2 k=min(n10)=2 r 0 1 2 3 Four cases 0s 512 s 512times2 s 512times3

s After ten collisions choose r from

01234hellip1023

38

Data Size Limitation

To avoid that any host occupies Ethernet too long the data size is smaller than 1500 bytes

If the size of a frame is too small adapters can not detect collision in time 10MHz 01sbit Within 512s 512sdivide01sbit= 512bits

=64 bytes can be sent Every frame must be larger than 64 bytes

Data size must be larger than 46 bytes

39

Effect of CSMACD

Unpredicable when the frame can be received

Not fair Bandwidth utilization degrades if heavy

loading Not suitable for real-time applications

40

Properties of An Ethernet

Shared bus technology( broadcast) Lowest level hardware does not support

addressing Best-effort delivery mechanism No central authority to grant access Each transmission is limited in duration

41

Part 4

IEEE 8023

42

IEEE 802 Series

Fiber UTP wireless cable

80211 8023

8022 LLC (Logic Link Control)

SMTP FTPHTTP

TCP UDP

SNMP DNS

IP

Ethernet802128024 8025

bull8023 CDMACD

bull8024 Token-bus

bull8025 Token-ring

bull80211 Wireless LAN

bull80212 100VG-AnyLAN

43

IEEE 8023 Protocol

Ethernet is compatible to 8023 Length of bytes in LLC

Preamble SourceDestination Length Data from LLC FCS

Bytes 8 6 6 2 46-1500 4

64-1518 bytes

44

Flow Chart of IEEE 8023傳送訊框

組成訊框

線上有訊號

訊框過短( )衝撞

檢查碼正確

傳送訊框

發生衝撞

傳送完畢

jamming送出signal

i=i+1

i gt 16

計算延遲時間

等待延遲時間

傳送失敗傳送成功

Y es

No

No

No

Y es

Y es Y es

No

接收訊框

開始接收

接收完畢

位址辨識成功

尚有多餘位元

刪除訊框頭尾

長度錯誤對齊錯誤

Y es

No

No

No

Y es

Y es

Y es

接收成功訊框錯誤

長度欄位內容正確

No

Y es No

Y es

No

Page 27: 1 Introduction of Ethernet Metcalfe’s Ethernet sketch Also refer to nfhuang/chap04.htm

27

Part 3

Multiple Access in

Ethernet

28

Sending an Ethernet Frame

Broadcast If there are two computers send data at

the same time two frames will collide A collision occurs Receivers discards these frames

CSMACD( Carrier Sense Multiple Access Collision Detection ) is used

Best Effect

29

CSMACD

Carrier Sense 表示網路卡要對 carrier 進行監測判斷網路線上是否有資料的傳送

Multiple Access 指出這種機制的目的是要讓多個網路卡可以在同一個 carrier 上存取資料

Collision Detection 表示 collision 是會發生的必須靠 detection的機制來判斷是否有 collision

30

Ethernet CSMACD algorithm (12)

1 NIC receives datagram from network layer and creates frame

2 If NIC senses channel idle starts frame transmission

If NIC senses channel busy waits until channel idle and then transmits

3 If NIC transmits entire frame without detecting another transmission NIC is done with frame

31

Ethernet CSMACD algorithm (22)

4 If NIC detects another transmission while transmitting aborts and sends jam signal Jam Signal make sure all other transmitters

are aware of collision 48 bits

5 After aborting NIC enters exponential backoff NIC chooses K at random from 012hellip2m-1

after the m th collision

NIC waits K512 bit times returns to Step 2

32

No Collision Occurs

A電腦 B電腦

A電腦 B電腦A frame開始送出

A電腦 B電腦

B聽到網路上有資 料 必須等待

A collision確定沒有繼續送資料

time=0

time=512s

Ex 10BaseT

why

33

Collision Occurs

If host B sends it frame before getting Arsquos frame a collision occurs

Host A finds noise treat it as a collision

The worst case A finds noise after a

round-trip propagation delay time

A電腦 B電腦B frame開始送出

A電腦 B電腦A frame開始送出

A電腦 B電腦collision發生

A電腦 B電腦

A collision發現接著送出

jamming signal

B collision發現

34

How Long to Find Collision

Round-trip propagation delay is 512 s for 10Mbps Ethernet

Host A must listen at least 512 s and know whether a collision occurs or not

A電腦 B電腦B frame開始送出

A電腦 B電腦A 開始送出

frame

A電腦 B電腦collision發生

A電腦 B電腦

A collision發現接著送出

Jamming signal

B collisionB發現 也 Jamming siganl會送

35

CSMACD Random Time Delay (12)

Let two collided hosts retransmit frames at a different time Host generates a random time delay (r) r 0

1 2k-1 n the number of collisions( n16) k = min (n 10)

Retransmit the frame after r Exponential backoff algorithm

The random time delay is round-trip propagation delay r For 10BaseT 512 sr

36

CSMACD Random Time Delay (22)

Goal adapt retransmission attempts to estimated current load Heavy load random wait will be

longer

37

Examples of Binary Exponential Backoff Algorithm

First collision n=1 k=min(n10)=1 r 0 1 Probability=12 to send frame immediately Probability=12 to send frame after 512 s

Second collision n=2 k=min(n10)=2 r 0 1 2 3 Four cases 0s 512 s 512times2 s 512times3

s After ten collisions choose r from

01234hellip1023

38

Data Size Limitation

To avoid that any host occupies Ethernet too long the data size is smaller than 1500 bytes

If the size of a frame is too small adapters can not detect collision in time 10MHz 01sbit Within 512s 512sdivide01sbit= 512bits

=64 bytes can be sent Every frame must be larger than 64 bytes

Data size must be larger than 46 bytes

39

Effect of CSMACD

Unpredicable when the frame can be received

Not fair Bandwidth utilization degrades if heavy

loading Not suitable for real-time applications

40

Properties of An Ethernet

Shared bus technology( broadcast) Lowest level hardware does not support

addressing Best-effort delivery mechanism No central authority to grant access Each transmission is limited in duration

41

Part 4

IEEE 8023

42

IEEE 802 Series

Fiber UTP wireless cable

80211 8023

8022 LLC (Logic Link Control)

SMTP FTPHTTP

TCP UDP

SNMP DNS

IP

Ethernet802128024 8025

bull8023 CDMACD

bull8024 Token-bus

bull8025 Token-ring

bull80211 Wireless LAN

bull80212 100VG-AnyLAN

43

IEEE 8023 Protocol

Ethernet is compatible to 8023 Length of bytes in LLC

Preamble SourceDestination Length Data from LLC FCS

Bytes 8 6 6 2 46-1500 4

64-1518 bytes

44

Flow Chart of IEEE 8023傳送訊框

組成訊框

線上有訊號

訊框過短( )衝撞

檢查碼正確

傳送訊框

發生衝撞

傳送完畢

jamming送出signal

i=i+1

i gt 16

計算延遲時間

等待延遲時間

傳送失敗傳送成功

Y es

No

No

No

Y es

Y es Y es

No

接收訊框

開始接收

接收完畢

位址辨識成功

尚有多餘位元

刪除訊框頭尾

長度錯誤對齊錯誤

Y es

No

No

No

Y es

Y es

Y es

接收成功訊框錯誤

長度欄位內容正確

No

Y es No

Y es

No

Page 28: 1 Introduction of Ethernet Metcalfe’s Ethernet sketch Also refer to nfhuang/chap04.htm

28

Sending an Ethernet Frame

Broadcast If there are two computers send data at

the same time two frames will collide A collision occurs Receivers discards these frames

CSMACD( Carrier Sense Multiple Access Collision Detection ) is used

Best Effect

29

CSMACD

Carrier Sense 表示網路卡要對 carrier 進行監測判斷網路線上是否有資料的傳送

Multiple Access 指出這種機制的目的是要讓多個網路卡可以在同一個 carrier 上存取資料

Collision Detection 表示 collision 是會發生的必須靠 detection的機制來判斷是否有 collision

30

Ethernet CSMACD algorithm (12)

1 NIC receives datagram from network layer and creates frame

2 If NIC senses channel idle starts frame transmission

If NIC senses channel busy waits until channel idle and then transmits

3 If NIC transmits entire frame without detecting another transmission NIC is done with frame

31

Ethernet CSMACD algorithm (22)

4 If NIC detects another transmission while transmitting aborts and sends jam signal Jam Signal make sure all other transmitters

are aware of collision 48 bits

5 After aborting NIC enters exponential backoff NIC chooses K at random from 012hellip2m-1

after the m th collision

NIC waits K512 bit times returns to Step 2

32

No Collision Occurs

A電腦 B電腦

A電腦 B電腦A frame開始送出

A電腦 B電腦

B聽到網路上有資 料 必須等待

A collision確定沒有繼續送資料

time=0

time=512s

Ex 10BaseT

why

33

Collision Occurs

If host B sends it frame before getting Arsquos frame a collision occurs

Host A finds noise treat it as a collision

The worst case A finds noise after a

round-trip propagation delay time

A電腦 B電腦B frame開始送出

A電腦 B電腦A frame開始送出

A電腦 B電腦collision發生

A電腦 B電腦

A collision發現接著送出

jamming signal

B collision發現

34

How Long to Find Collision

Round-trip propagation delay is 512 s for 10Mbps Ethernet

Host A must listen at least 512 s and know whether a collision occurs or not

A電腦 B電腦B frame開始送出

A電腦 B電腦A 開始送出

frame

A電腦 B電腦collision發生

A電腦 B電腦

A collision發現接著送出

Jamming signal

B collisionB發現 也 Jamming siganl會送

35

CSMACD Random Time Delay (12)

Let two collided hosts retransmit frames at a different time Host generates a random time delay (r) r 0

1 2k-1 n the number of collisions( n16) k = min (n 10)

Retransmit the frame after r Exponential backoff algorithm

The random time delay is round-trip propagation delay r For 10BaseT 512 sr

36

CSMACD Random Time Delay (22)

Goal adapt retransmission attempts to estimated current load Heavy load random wait will be

longer

37

Examples of Binary Exponential Backoff Algorithm

First collision n=1 k=min(n10)=1 r 0 1 Probability=12 to send frame immediately Probability=12 to send frame after 512 s

Second collision n=2 k=min(n10)=2 r 0 1 2 3 Four cases 0s 512 s 512times2 s 512times3

s After ten collisions choose r from

01234hellip1023

38

Data Size Limitation

To avoid that any host occupies Ethernet too long the data size is smaller than 1500 bytes

If the size of a frame is too small adapters can not detect collision in time 10MHz 01sbit Within 512s 512sdivide01sbit= 512bits

=64 bytes can be sent Every frame must be larger than 64 bytes

Data size must be larger than 46 bytes

39

Effect of CSMACD

Unpredicable when the frame can be received

Not fair Bandwidth utilization degrades if heavy

loading Not suitable for real-time applications

40

Properties of An Ethernet

Shared bus technology( broadcast) Lowest level hardware does not support

addressing Best-effort delivery mechanism No central authority to grant access Each transmission is limited in duration

41

Part 4

IEEE 8023

42

IEEE 802 Series

Fiber UTP wireless cable

80211 8023

8022 LLC (Logic Link Control)

SMTP FTPHTTP

TCP UDP

SNMP DNS

IP

Ethernet802128024 8025

bull8023 CDMACD

bull8024 Token-bus

bull8025 Token-ring

bull80211 Wireless LAN

bull80212 100VG-AnyLAN

43

IEEE 8023 Protocol

Ethernet is compatible to 8023 Length of bytes in LLC

Preamble SourceDestination Length Data from LLC FCS

Bytes 8 6 6 2 46-1500 4

64-1518 bytes

44

Flow Chart of IEEE 8023傳送訊框

組成訊框

線上有訊號

訊框過短( )衝撞

檢查碼正確

傳送訊框

發生衝撞

傳送完畢

jamming送出signal

i=i+1

i gt 16

計算延遲時間

等待延遲時間

傳送失敗傳送成功

Y es

No

No

No

Y es

Y es Y es

No

接收訊框

開始接收

接收完畢

位址辨識成功

尚有多餘位元

刪除訊框頭尾

長度錯誤對齊錯誤

Y es

No

No

No

Y es

Y es

Y es

接收成功訊框錯誤

長度欄位內容正確

No

Y es No

Y es

No

Page 29: 1 Introduction of Ethernet Metcalfe’s Ethernet sketch Also refer to nfhuang/chap04.htm

29

CSMACD

Carrier Sense 表示網路卡要對 carrier 進行監測判斷網路線上是否有資料的傳送

Multiple Access 指出這種機制的目的是要讓多個網路卡可以在同一個 carrier 上存取資料

Collision Detection 表示 collision 是會發生的必須靠 detection的機制來判斷是否有 collision

30

Ethernet CSMACD algorithm (12)

1 NIC receives datagram from network layer and creates frame

2 If NIC senses channel idle starts frame transmission

If NIC senses channel busy waits until channel idle and then transmits

3 If NIC transmits entire frame without detecting another transmission NIC is done with frame

31

Ethernet CSMACD algorithm (22)

4 If NIC detects another transmission while transmitting aborts and sends jam signal Jam Signal make sure all other transmitters

are aware of collision 48 bits

5 After aborting NIC enters exponential backoff NIC chooses K at random from 012hellip2m-1

after the m th collision

NIC waits K512 bit times returns to Step 2

32

No Collision Occurs

A電腦 B電腦

A電腦 B電腦A frame開始送出

A電腦 B電腦

B聽到網路上有資 料 必須等待

A collision確定沒有繼續送資料

time=0

time=512s

Ex 10BaseT

why

33

Collision Occurs

If host B sends it frame before getting Arsquos frame a collision occurs

Host A finds noise treat it as a collision

The worst case A finds noise after a

round-trip propagation delay time

A電腦 B電腦B frame開始送出

A電腦 B電腦A frame開始送出

A電腦 B電腦collision發生

A電腦 B電腦

A collision發現接著送出

jamming signal

B collision發現

34

How Long to Find Collision

Round-trip propagation delay is 512 s for 10Mbps Ethernet

Host A must listen at least 512 s and know whether a collision occurs or not

A電腦 B電腦B frame開始送出

A電腦 B電腦A 開始送出

frame

A電腦 B電腦collision發生

A電腦 B電腦

A collision發現接著送出

Jamming signal

B collisionB發現 也 Jamming siganl會送

35

CSMACD Random Time Delay (12)

Let two collided hosts retransmit frames at a different time Host generates a random time delay (r) r 0

1 2k-1 n the number of collisions( n16) k = min (n 10)

Retransmit the frame after r Exponential backoff algorithm

The random time delay is round-trip propagation delay r For 10BaseT 512 sr

36

CSMACD Random Time Delay (22)

Goal adapt retransmission attempts to estimated current load Heavy load random wait will be

longer

37

Examples of Binary Exponential Backoff Algorithm

First collision n=1 k=min(n10)=1 r 0 1 Probability=12 to send frame immediately Probability=12 to send frame after 512 s

Second collision n=2 k=min(n10)=2 r 0 1 2 3 Four cases 0s 512 s 512times2 s 512times3

s After ten collisions choose r from

01234hellip1023

38

Data Size Limitation

To avoid that any host occupies Ethernet too long the data size is smaller than 1500 bytes

If the size of a frame is too small adapters can not detect collision in time 10MHz 01sbit Within 512s 512sdivide01sbit= 512bits

=64 bytes can be sent Every frame must be larger than 64 bytes

Data size must be larger than 46 bytes

39

Effect of CSMACD

Unpredicable when the frame can be received

Not fair Bandwidth utilization degrades if heavy

loading Not suitable for real-time applications

40

Properties of An Ethernet

Shared bus technology( broadcast) Lowest level hardware does not support

addressing Best-effort delivery mechanism No central authority to grant access Each transmission is limited in duration

41

Part 4

IEEE 8023

42

IEEE 802 Series

Fiber UTP wireless cable

80211 8023

8022 LLC (Logic Link Control)

SMTP FTPHTTP

TCP UDP

SNMP DNS

IP

Ethernet802128024 8025

bull8023 CDMACD

bull8024 Token-bus

bull8025 Token-ring

bull80211 Wireless LAN

bull80212 100VG-AnyLAN

43

IEEE 8023 Protocol

Ethernet is compatible to 8023 Length of bytes in LLC

Preamble SourceDestination Length Data from LLC FCS

Bytes 8 6 6 2 46-1500 4

64-1518 bytes

44

Flow Chart of IEEE 8023傳送訊框

組成訊框

線上有訊號

訊框過短( )衝撞

檢查碼正確

傳送訊框

發生衝撞

傳送完畢

jamming送出signal

i=i+1

i gt 16

計算延遲時間

等待延遲時間

傳送失敗傳送成功

Y es

No

No

No

Y es

Y es Y es

No

接收訊框

開始接收

接收完畢

位址辨識成功

尚有多餘位元

刪除訊框頭尾

長度錯誤對齊錯誤

Y es

No

No

No

Y es

Y es

Y es

接收成功訊框錯誤

長度欄位內容正確

No

Y es No

Y es

No

Page 30: 1 Introduction of Ethernet Metcalfe’s Ethernet sketch Also refer to nfhuang/chap04.htm

30

Ethernet CSMACD algorithm (12)

1 NIC receives datagram from network layer and creates frame

2 If NIC senses channel idle starts frame transmission

If NIC senses channel busy waits until channel idle and then transmits

3 If NIC transmits entire frame without detecting another transmission NIC is done with frame

31

Ethernet CSMACD algorithm (22)

4 If NIC detects another transmission while transmitting aborts and sends jam signal Jam Signal make sure all other transmitters

are aware of collision 48 bits

5 After aborting NIC enters exponential backoff NIC chooses K at random from 012hellip2m-1

after the m th collision

NIC waits K512 bit times returns to Step 2

32

No Collision Occurs

A電腦 B電腦

A電腦 B電腦A frame開始送出

A電腦 B電腦

B聽到網路上有資 料 必須等待

A collision確定沒有繼續送資料

time=0

time=512s

Ex 10BaseT

why

33

Collision Occurs

If host B sends it frame before getting Arsquos frame a collision occurs

Host A finds noise treat it as a collision

The worst case A finds noise after a

round-trip propagation delay time

A電腦 B電腦B frame開始送出

A電腦 B電腦A frame開始送出

A電腦 B電腦collision發生

A電腦 B電腦

A collision發現接著送出

jamming signal

B collision發現

34

How Long to Find Collision

Round-trip propagation delay is 512 s for 10Mbps Ethernet

Host A must listen at least 512 s and know whether a collision occurs or not

A電腦 B電腦B frame開始送出

A電腦 B電腦A 開始送出

frame

A電腦 B電腦collision發生

A電腦 B電腦

A collision發現接著送出

Jamming signal

B collisionB發現 也 Jamming siganl會送

35

CSMACD Random Time Delay (12)

Let two collided hosts retransmit frames at a different time Host generates a random time delay (r) r 0

1 2k-1 n the number of collisions( n16) k = min (n 10)

Retransmit the frame after r Exponential backoff algorithm

The random time delay is round-trip propagation delay r For 10BaseT 512 sr

36

CSMACD Random Time Delay (22)

Goal adapt retransmission attempts to estimated current load Heavy load random wait will be

longer

37

Examples of Binary Exponential Backoff Algorithm

First collision n=1 k=min(n10)=1 r 0 1 Probability=12 to send frame immediately Probability=12 to send frame after 512 s

Second collision n=2 k=min(n10)=2 r 0 1 2 3 Four cases 0s 512 s 512times2 s 512times3

s After ten collisions choose r from

01234hellip1023

38

Data Size Limitation

To avoid that any host occupies Ethernet too long the data size is smaller than 1500 bytes

If the size of a frame is too small adapters can not detect collision in time 10MHz 01sbit Within 512s 512sdivide01sbit= 512bits

=64 bytes can be sent Every frame must be larger than 64 bytes

Data size must be larger than 46 bytes

39

Effect of CSMACD

Unpredicable when the frame can be received

Not fair Bandwidth utilization degrades if heavy

loading Not suitable for real-time applications

40

Properties of An Ethernet

Shared bus technology( broadcast) Lowest level hardware does not support

addressing Best-effort delivery mechanism No central authority to grant access Each transmission is limited in duration

41

Part 4

IEEE 8023

42

IEEE 802 Series

Fiber UTP wireless cable

80211 8023

8022 LLC (Logic Link Control)

SMTP FTPHTTP

TCP UDP

SNMP DNS

IP

Ethernet802128024 8025

bull8023 CDMACD

bull8024 Token-bus

bull8025 Token-ring

bull80211 Wireless LAN

bull80212 100VG-AnyLAN

43

IEEE 8023 Protocol

Ethernet is compatible to 8023 Length of bytes in LLC

Preamble SourceDestination Length Data from LLC FCS

Bytes 8 6 6 2 46-1500 4

64-1518 bytes

44

Flow Chart of IEEE 8023傳送訊框

組成訊框

線上有訊號

訊框過短( )衝撞

檢查碼正確

傳送訊框

發生衝撞

傳送完畢

jamming送出signal

i=i+1

i gt 16

計算延遲時間

等待延遲時間

傳送失敗傳送成功

Y es

No

No

No

Y es

Y es Y es

No

接收訊框

開始接收

接收完畢

位址辨識成功

尚有多餘位元

刪除訊框頭尾

長度錯誤對齊錯誤

Y es

No

No

No

Y es

Y es

Y es

接收成功訊框錯誤

長度欄位內容正確

No

Y es No

Y es

No

Page 31: 1 Introduction of Ethernet Metcalfe’s Ethernet sketch Also refer to nfhuang/chap04.htm

31

Ethernet CSMACD algorithm (22)

4 If NIC detects another transmission while transmitting aborts and sends jam signal Jam Signal make sure all other transmitters

are aware of collision 48 bits

5 After aborting NIC enters exponential backoff NIC chooses K at random from 012hellip2m-1

after the m th collision

NIC waits K512 bit times returns to Step 2

32

No Collision Occurs

A電腦 B電腦

A電腦 B電腦A frame開始送出

A電腦 B電腦

B聽到網路上有資 料 必須等待

A collision確定沒有繼續送資料

time=0

time=512s

Ex 10BaseT

why

33

Collision Occurs

If host B sends it frame before getting Arsquos frame a collision occurs

Host A finds noise treat it as a collision

The worst case A finds noise after a

round-trip propagation delay time

A電腦 B電腦B frame開始送出

A電腦 B電腦A frame開始送出

A電腦 B電腦collision發生

A電腦 B電腦

A collision發現接著送出

jamming signal

B collision發現

34

How Long to Find Collision

Round-trip propagation delay is 512 s for 10Mbps Ethernet

Host A must listen at least 512 s and know whether a collision occurs or not

A電腦 B電腦B frame開始送出

A電腦 B電腦A 開始送出

frame

A電腦 B電腦collision發生

A電腦 B電腦

A collision發現接著送出

Jamming signal

B collisionB發現 也 Jamming siganl會送

35

CSMACD Random Time Delay (12)

Let two collided hosts retransmit frames at a different time Host generates a random time delay (r) r 0

1 2k-1 n the number of collisions( n16) k = min (n 10)

Retransmit the frame after r Exponential backoff algorithm

The random time delay is round-trip propagation delay r For 10BaseT 512 sr

36

CSMACD Random Time Delay (22)

Goal adapt retransmission attempts to estimated current load Heavy load random wait will be

longer

37

Examples of Binary Exponential Backoff Algorithm

First collision n=1 k=min(n10)=1 r 0 1 Probability=12 to send frame immediately Probability=12 to send frame after 512 s

Second collision n=2 k=min(n10)=2 r 0 1 2 3 Four cases 0s 512 s 512times2 s 512times3

s After ten collisions choose r from

01234hellip1023

38

Data Size Limitation

To avoid that any host occupies Ethernet too long the data size is smaller than 1500 bytes

If the size of a frame is too small adapters can not detect collision in time 10MHz 01sbit Within 512s 512sdivide01sbit= 512bits

=64 bytes can be sent Every frame must be larger than 64 bytes

Data size must be larger than 46 bytes

39

Effect of CSMACD

Unpredicable when the frame can be received

Not fair Bandwidth utilization degrades if heavy

loading Not suitable for real-time applications

40

Properties of An Ethernet

Shared bus technology( broadcast) Lowest level hardware does not support

addressing Best-effort delivery mechanism No central authority to grant access Each transmission is limited in duration

41

Part 4

IEEE 8023

42

IEEE 802 Series

Fiber UTP wireless cable

80211 8023

8022 LLC (Logic Link Control)

SMTP FTPHTTP

TCP UDP

SNMP DNS

IP

Ethernet802128024 8025

bull8023 CDMACD

bull8024 Token-bus

bull8025 Token-ring

bull80211 Wireless LAN

bull80212 100VG-AnyLAN

43

IEEE 8023 Protocol

Ethernet is compatible to 8023 Length of bytes in LLC

Preamble SourceDestination Length Data from LLC FCS

Bytes 8 6 6 2 46-1500 4

64-1518 bytes

44

Flow Chart of IEEE 8023傳送訊框

組成訊框

線上有訊號

訊框過短( )衝撞

檢查碼正確

傳送訊框

發生衝撞

傳送完畢

jamming送出signal

i=i+1

i gt 16

計算延遲時間

等待延遲時間

傳送失敗傳送成功

Y es

No

No

No

Y es

Y es Y es

No

接收訊框

開始接收

接收完畢

位址辨識成功

尚有多餘位元

刪除訊框頭尾

長度錯誤對齊錯誤

Y es

No

No

No

Y es

Y es

Y es

接收成功訊框錯誤

長度欄位內容正確

No

Y es No

Y es

No

Page 32: 1 Introduction of Ethernet Metcalfe’s Ethernet sketch Also refer to nfhuang/chap04.htm

32

No Collision Occurs

A電腦 B電腦

A電腦 B電腦A frame開始送出

A電腦 B電腦

B聽到網路上有資 料 必須等待

A collision確定沒有繼續送資料

time=0

time=512s

Ex 10BaseT

why

33

Collision Occurs

If host B sends it frame before getting Arsquos frame a collision occurs

Host A finds noise treat it as a collision

The worst case A finds noise after a

round-trip propagation delay time

A電腦 B電腦B frame開始送出

A電腦 B電腦A frame開始送出

A電腦 B電腦collision發生

A電腦 B電腦

A collision發現接著送出

jamming signal

B collision發現

34

How Long to Find Collision

Round-trip propagation delay is 512 s for 10Mbps Ethernet

Host A must listen at least 512 s and know whether a collision occurs or not

A電腦 B電腦B frame開始送出

A電腦 B電腦A 開始送出

frame

A電腦 B電腦collision發生

A電腦 B電腦

A collision發現接著送出

Jamming signal

B collisionB發現 也 Jamming siganl會送

35

CSMACD Random Time Delay (12)

Let two collided hosts retransmit frames at a different time Host generates a random time delay (r) r 0

1 2k-1 n the number of collisions( n16) k = min (n 10)

Retransmit the frame after r Exponential backoff algorithm

The random time delay is round-trip propagation delay r For 10BaseT 512 sr

36

CSMACD Random Time Delay (22)

Goal adapt retransmission attempts to estimated current load Heavy load random wait will be

longer

37

Examples of Binary Exponential Backoff Algorithm

First collision n=1 k=min(n10)=1 r 0 1 Probability=12 to send frame immediately Probability=12 to send frame after 512 s

Second collision n=2 k=min(n10)=2 r 0 1 2 3 Four cases 0s 512 s 512times2 s 512times3

s After ten collisions choose r from

01234hellip1023

38

Data Size Limitation

To avoid that any host occupies Ethernet too long the data size is smaller than 1500 bytes

If the size of a frame is too small adapters can not detect collision in time 10MHz 01sbit Within 512s 512sdivide01sbit= 512bits

=64 bytes can be sent Every frame must be larger than 64 bytes

Data size must be larger than 46 bytes

39

Effect of CSMACD

Unpredicable when the frame can be received

Not fair Bandwidth utilization degrades if heavy

loading Not suitable for real-time applications

40

Properties of An Ethernet

Shared bus technology( broadcast) Lowest level hardware does not support

addressing Best-effort delivery mechanism No central authority to grant access Each transmission is limited in duration

41

Part 4

IEEE 8023

42

IEEE 802 Series

Fiber UTP wireless cable

80211 8023

8022 LLC (Logic Link Control)

SMTP FTPHTTP

TCP UDP

SNMP DNS

IP

Ethernet802128024 8025

bull8023 CDMACD

bull8024 Token-bus

bull8025 Token-ring

bull80211 Wireless LAN

bull80212 100VG-AnyLAN

43

IEEE 8023 Protocol

Ethernet is compatible to 8023 Length of bytes in LLC

Preamble SourceDestination Length Data from LLC FCS

Bytes 8 6 6 2 46-1500 4

64-1518 bytes

44

Flow Chart of IEEE 8023傳送訊框

組成訊框

線上有訊號

訊框過短( )衝撞

檢查碼正確

傳送訊框

發生衝撞

傳送完畢

jamming送出signal

i=i+1

i gt 16

計算延遲時間

等待延遲時間

傳送失敗傳送成功

Y es

No

No

No

Y es

Y es Y es

No

接收訊框

開始接收

接收完畢

位址辨識成功

尚有多餘位元

刪除訊框頭尾

長度錯誤對齊錯誤

Y es

No

No

No

Y es

Y es

Y es

接收成功訊框錯誤

長度欄位內容正確

No

Y es No

Y es

No

Page 33: 1 Introduction of Ethernet Metcalfe’s Ethernet sketch Also refer to nfhuang/chap04.htm

33

Collision Occurs

If host B sends it frame before getting Arsquos frame a collision occurs

Host A finds noise treat it as a collision

The worst case A finds noise after a

round-trip propagation delay time

A電腦 B電腦B frame開始送出

A電腦 B電腦A frame開始送出

A電腦 B電腦collision發生

A電腦 B電腦

A collision發現接著送出

jamming signal

B collision發現

34

How Long to Find Collision

Round-trip propagation delay is 512 s for 10Mbps Ethernet

Host A must listen at least 512 s and know whether a collision occurs or not

A電腦 B電腦B frame開始送出

A電腦 B電腦A 開始送出

frame

A電腦 B電腦collision發生

A電腦 B電腦

A collision發現接著送出

Jamming signal

B collisionB發現 也 Jamming siganl會送

35

CSMACD Random Time Delay (12)

Let two collided hosts retransmit frames at a different time Host generates a random time delay (r) r 0

1 2k-1 n the number of collisions( n16) k = min (n 10)

Retransmit the frame after r Exponential backoff algorithm

The random time delay is round-trip propagation delay r For 10BaseT 512 sr

36

CSMACD Random Time Delay (22)

Goal adapt retransmission attempts to estimated current load Heavy load random wait will be

longer

37

Examples of Binary Exponential Backoff Algorithm

First collision n=1 k=min(n10)=1 r 0 1 Probability=12 to send frame immediately Probability=12 to send frame after 512 s

Second collision n=2 k=min(n10)=2 r 0 1 2 3 Four cases 0s 512 s 512times2 s 512times3

s After ten collisions choose r from

01234hellip1023

38

Data Size Limitation

To avoid that any host occupies Ethernet too long the data size is smaller than 1500 bytes

If the size of a frame is too small adapters can not detect collision in time 10MHz 01sbit Within 512s 512sdivide01sbit= 512bits

=64 bytes can be sent Every frame must be larger than 64 bytes

Data size must be larger than 46 bytes

39

Effect of CSMACD

Unpredicable when the frame can be received

Not fair Bandwidth utilization degrades if heavy

loading Not suitable for real-time applications

40

Properties of An Ethernet

Shared bus technology( broadcast) Lowest level hardware does not support

addressing Best-effort delivery mechanism No central authority to grant access Each transmission is limited in duration

41

Part 4

IEEE 8023

42

IEEE 802 Series

Fiber UTP wireless cable

80211 8023

8022 LLC (Logic Link Control)

SMTP FTPHTTP

TCP UDP

SNMP DNS

IP

Ethernet802128024 8025

bull8023 CDMACD

bull8024 Token-bus

bull8025 Token-ring

bull80211 Wireless LAN

bull80212 100VG-AnyLAN

43

IEEE 8023 Protocol

Ethernet is compatible to 8023 Length of bytes in LLC

Preamble SourceDestination Length Data from LLC FCS

Bytes 8 6 6 2 46-1500 4

64-1518 bytes

44

Flow Chart of IEEE 8023傳送訊框

組成訊框

線上有訊號

訊框過短( )衝撞

檢查碼正確

傳送訊框

發生衝撞

傳送完畢

jamming送出signal

i=i+1

i gt 16

計算延遲時間

等待延遲時間

傳送失敗傳送成功

Y es

No

No

No

Y es

Y es Y es

No

接收訊框

開始接收

接收完畢

位址辨識成功

尚有多餘位元

刪除訊框頭尾

長度錯誤對齊錯誤

Y es

No

No

No

Y es

Y es

Y es

接收成功訊框錯誤

長度欄位內容正確

No

Y es No

Y es

No

Page 34: 1 Introduction of Ethernet Metcalfe’s Ethernet sketch Also refer to nfhuang/chap04.htm

34

How Long to Find Collision

Round-trip propagation delay is 512 s for 10Mbps Ethernet

Host A must listen at least 512 s and know whether a collision occurs or not

A電腦 B電腦B frame開始送出

A電腦 B電腦A 開始送出

frame

A電腦 B電腦collision發生

A電腦 B電腦

A collision發現接著送出

Jamming signal

B collisionB發現 也 Jamming siganl會送

35

CSMACD Random Time Delay (12)

Let two collided hosts retransmit frames at a different time Host generates a random time delay (r) r 0

1 2k-1 n the number of collisions( n16) k = min (n 10)

Retransmit the frame after r Exponential backoff algorithm

The random time delay is round-trip propagation delay r For 10BaseT 512 sr

36

CSMACD Random Time Delay (22)

Goal adapt retransmission attempts to estimated current load Heavy load random wait will be

longer

37

Examples of Binary Exponential Backoff Algorithm

First collision n=1 k=min(n10)=1 r 0 1 Probability=12 to send frame immediately Probability=12 to send frame after 512 s

Second collision n=2 k=min(n10)=2 r 0 1 2 3 Four cases 0s 512 s 512times2 s 512times3

s After ten collisions choose r from

01234hellip1023

38

Data Size Limitation

To avoid that any host occupies Ethernet too long the data size is smaller than 1500 bytes

If the size of a frame is too small adapters can not detect collision in time 10MHz 01sbit Within 512s 512sdivide01sbit= 512bits

=64 bytes can be sent Every frame must be larger than 64 bytes

Data size must be larger than 46 bytes

39

Effect of CSMACD

Unpredicable when the frame can be received

Not fair Bandwidth utilization degrades if heavy

loading Not suitable for real-time applications

40

Properties of An Ethernet

Shared bus technology( broadcast) Lowest level hardware does not support

addressing Best-effort delivery mechanism No central authority to grant access Each transmission is limited in duration

41

Part 4

IEEE 8023

42

IEEE 802 Series

Fiber UTP wireless cable

80211 8023

8022 LLC (Logic Link Control)

SMTP FTPHTTP

TCP UDP

SNMP DNS

IP

Ethernet802128024 8025

bull8023 CDMACD

bull8024 Token-bus

bull8025 Token-ring

bull80211 Wireless LAN

bull80212 100VG-AnyLAN

43

IEEE 8023 Protocol

Ethernet is compatible to 8023 Length of bytes in LLC

Preamble SourceDestination Length Data from LLC FCS

Bytes 8 6 6 2 46-1500 4

64-1518 bytes

44

Flow Chart of IEEE 8023傳送訊框

組成訊框

線上有訊號

訊框過短( )衝撞

檢查碼正確

傳送訊框

發生衝撞

傳送完畢

jamming送出signal

i=i+1

i gt 16

計算延遲時間

等待延遲時間

傳送失敗傳送成功

Y es

No

No

No

Y es

Y es Y es

No

接收訊框

開始接收

接收完畢

位址辨識成功

尚有多餘位元

刪除訊框頭尾

長度錯誤對齊錯誤

Y es

No

No

No

Y es

Y es

Y es

接收成功訊框錯誤

長度欄位內容正確

No

Y es No

Y es

No

Page 35: 1 Introduction of Ethernet Metcalfe’s Ethernet sketch Also refer to nfhuang/chap04.htm

35

CSMACD Random Time Delay (12)

Let two collided hosts retransmit frames at a different time Host generates a random time delay (r) r 0

1 2k-1 n the number of collisions( n16) k = min (n 10)

Retransmit the frame after r Exponential backoff algorithm

The random time delay is round-trip propagation delay r For 10BaseT 512 sr

36

CSMACD Random Time Delay (22)

Goal adapt retransmission attempts to estimated current load Heavy load random wait will be

longer

37

Examples of Binary Exponential Backoff Algorithm

First collision n=1 k=min(n10)=1 r 0 1 Probability=12 to send frame immediately Probability=12 to send frame after 512 s

Second collision n=2 k=min(n10)=2 r 0 1 2 3 Four cases 0s 512 s 512times2 s 512times3

s After ten collisions choose r from

01234hellip1023

38

Data Size Limitation

To avoid that any host occupies Ethernet too long the data size is smaller than 1500 bytes

If the size of a frame is too small adapters can not detect collision in time 10MHz 01sbit Within 512s 512sdivide01sbit= 512bits

=64 bytes can be sent Every frame must be larger than 64 bytes

Data size must be larger than 46 bytes

39

Effect of CSMACD

Unpredicable when the frame can be received

Not fair Bandwidth utilization degrades if heavy

loading Not suitable for real-time applications

40

Properties of An Ethernet

Shared bus technology( broadcast) Lowest level hardware does not support

addressing Best-effort delivery mechanism No central authority to grant access Each transmission is limited in duration

41

Part 4

IEEE 8023

42

IEEE 802 Series

Fiber UTP wireless cable

80211 8023

8022 LLC (Logic Link Control)

SMTP FTPHTTP

TCP UDP

SNMP DNS

IP

Ethernet802128024 8025

bull8023 CDMACD

bull8024 Token-bus

bull8025 Token-ring

bull80211 Wireless LAN

bull80212 100VG-AnyLAN

43

IEEE 8023 Protocol

Ethernet is compatible to 8023 Length of bytes in LLC

Preamble SourceDestination Length Data from LLC FCS

Bytes 8 6 6 2 46-1500 4

64-1518 bytes

44

Flow Chart of IEEE 8023傳送訊框

組成訊框

線上有訊號

訊框過短( )衝撞

檢查碼正確

傳送訊框

發生衝撞

傳送完畢

jamming送出signal

i=i+1

i gt 16

計算延遲時間

等待延遲時間

傳送失敗傳送成功

Y es

No

No

No

Y es

Y es Y es

No

接收訊框

開始接收

接收完畢

位址辨識成功

尚有多餘位元

刪除訊框頭尾

長度錯誤對齊錯誤

Y es

No

No

No

Y es

Y es

Y es

接收成功訊框錯誤

長度欄位內容正確

No

Y es No

Y es

No

Page 36: 1 Introduction of Ethernet Metcalfe’s Ethernet sketch Also refer to nfhuang/chap04.htm

36

CSMACD Random Time Delay (22)

Goal adapt retransmission attempts to estimated current load Heavy load random wait will be

longer

37

Examples of Binary Exponential Backoff Algorithm

First collision n=1 k=min(n10)=1 r 0 1 Probability=12 to send frame immediately Probability=12 to send frame after 512 s

Second collision n=2 k=min(n10)=2 r 0 1 2 3 Four cases 0s 512 s 512times2 s 512times3

s After ten collisions choose r from

01234hellip1023

38

Data Size Limitation

To avoid that any host occupies Ethernet too long the data size is smaller than 1500 bytes

If the size of a frame is too small adapters can not detect collision in time 10MHz 01sbit Within 512s 512sdivide01sbit= 512bits

=64 bytes can be sent Every frame must be larger than 64 bytes

Data size must be larger than 46 bytes

39

Effect of CSMACD

Unpredicable when the frame can be received

Not fair Bandwidth utilization degrades if heavy

loading Not suitable for real-time applications

40

Properties of An Ethernet

Shared bus technology( broadcast) Lowest level hardware does not support

addressing Best-effort delivery mechanism No central authority to grant access Each transmission is limited in duration

41

Part 4

IEEE 8023

42

IEEE 802 Series

Fiber UTP wireless cable

80211 8023

8022 LLC (Logic Link Control)

SMTP FTPHTTP

TCP UDP

SNMP DNS

IP

Ethernet802128024 8025

bull8023 CDMACD

bull8024 Token-bus

bull8025 Token-ring

bull80211 Wireless LAN

bull80212 100VG-AnyLAN

43

IEEE 8023 Protocol

Ethernet is compatible to 8023 Length of bytes in LLC

Preamble SourceDestination Length Data from LLC FCS

Bytes 8 6 6 2 46-1500 4

64-1518 bytes

44

Flow Chart of IEEE 8023傳送訊框

組成訊框

線上有訊號

訊框過短( )衝撞

檢查碼正確

傳送訊框

發生衝撞

傳送完畢

jamming送出signal

i=i+1

i gt 16

計算延遲時間

等待延遲時間

傳送失敗傳送成功

Y es

No

No

No

Y es

Y es Y es

No

接收訊框

開始接收

接收完畢

位址辨識成功

尚有多餘位元

刪除訊框頭尾

長度錯誤對齊錯誤

Y es

No

No

No

Y es

Y es

Y es

接收成功訊框錯誤

長度欄位內容正確

No

Y es No

Y es

No

Page 37: 1 Introduction of Ethernet Metcalfe’s Ethernet sketch Also refer to nfhuang/chap04.htm

37

Examples of Binary Exponential Backoff Algorithm

First collision n=1 k=min(n10)=1 r 0 1 Probability=12 to send frame immediately Probability=12 to send frame after 512 s

Second collision n=2 k=min(n10)=2 r 0 1 2 3 Four cases 0s 512 s 512times2 s 512times3

s After ten collisions choose r from

01234hellip1023

38

Data Size Limitation

To avoid that any host occupies Ethernet too long the data size is smaller than 1500 bytes

If the size of a frame is too small adapters can not detect collision in time 10MHz 01sbit Within 512s 512sdivide01sbit= 512bits

=64 bytes can be sent Every frame must be larger than 64 bytes

Data size must be larger than 46 bytes

39

Effect of CSMACD

Unpredicable when the frame can be received

Not fair Bandwidth utilization degrades if heavy

loading Not suitable for real-time applications

40

Properties of An Ethernet

Shared bus technology( broadcast) Lowest level hardware does not support

addressing Best-effort delivery mechanism No central authority to grant access Each transmission is limited in duration

41

Part 4

IEEE 8023

42

IEEE 802 Series

Fiber UTP wireless cable

80211 8023

8022 LLC (Logic Link Control)

SMTP FTPHTTP

TCP UDP

SNMP DNS

IP

Ethernet802128024 8025

bull8023 CDMACD

bull8024 Token-bus

bull8025 Token-ring

bull80211 Wireless LAN

bull80212 100VG-AnyLAN

43

IEEE 8023 Protocol

Ethernet is compatible to 8023 Length of bytes in LLC

Preamble SourceDestination Length Data from LLC FCS

Bytes 8 6 6 2 46-1500 4

64-1518 bytes

44

Flow Chart of IEEE 8023傳送訊框

組成訊框

線上有訊號

訊框過短( )衝撞

檢查碼正確

傳送訊框

發生衝撞

傳送完畢

jamming送出signal

i=i+1

i gt 16

計算延遲時間

等待延遲時間

傳送失敗傳送成功

Y es

No

No

No

Y es

Y es Y es

No

接收訊框

開始接收

接收完畢

位址辨識成功

尚有多餘位元

刪除訊框頭尾

長度錯誤對齊錯誤

Y es

No

No

No

Y es

Y es

Y es

接收成功訊框錯誤

長度欄位內容正確

No

Y es No

Y es

No

Page 38: 1 Introduction of Ethernet Metcalfe’s Ethernet sketch Also refer to nfhuang/chap04.htm

38

Data Size Limitation

To avoid that any host occupies Ethernet too long the data size is smaller than 1500 bytes

If the size of a frame is too small adapters can not detect collision in time 10MHz 01sbit Within 512s 512sdivide01sbit= 512bits

=64 bytes can be sent Every frame must be larger than 64 bytes

Data size must be larger than 46 bytes

39

Effect of CSMACD

Unpredicable when the frame can be received

Not fair Bandwidth utilization degrades if heavy

loading Not suitable for real-time applications

40

Properties of An Ethernet

Shared bus technology( broadcast) Lowest level hardware does not support

addressing Best-effort delivery mechanism No central authority to grant access Each transmission is limited in duration

41

Part 4

IEEE 8023

42

IEEE 802 Series

Fiber UTP wireless cable

80211 8023

8022 LLC (Logic Link Control)

SMTP FTPHTTP

TCP UDP

SNMP DNS

IP

Ethernet802128024 8025

bull8023 CDMACD

bull8024 Token-bus

bull8025 Token-ring

bull80211 Wireless LAN

bull80212 100VG-AnyLAN

43

IEEE 8023 Protocol

Ethernet is compatible to 8023 Length of bytes in LLC

Preamble SourceDestination Length Data from LLC FCS

Bytes 8 6 6 2 46-1500 4

64-1518 bytes

44

Flow Chart of IEEE 8023傳送訊框

組成訊框

線上有訊號

訊框過短( )衝撞

檢查碼正確

傳送訊框

發生衝撞

傳送完畢

jamming送出signal

i=i+1

i gt 16

計算延遲時間

等待延遲時間

傳送失敗傳送成功

Y es

No

No

No

Y es

Y es Y es

No

接收訊框

開始接收

接收完畢

位址辨識成功

尚有多餘位元

刪除訊框頭尾

長度錯誤對齊錯誤

Y es

No

No

No

Y es

Y es

Y es

接收成功訊框錯誤

長度欄位內容正確

No

Y es No

Y es

No

Page 39: 1 Introduction of Ethernet Metcalfe’s Ethernet sketch Also refer to nfhuang/chap04.htm

39

Effect of CSMACD

Unpredicable when the frame can be received

Not fair Bandwidth utilization degrades if heavy

loading Not suitable for real-time applications

40

Properties of An Ethernet

Shared bus technology( broadcast) Lowest level hardware does not support

addressing Best-effort delivery mechanism No central authority to grant access Each transmission is limited in duration

41

Part 4

IEEE 8023

42

IEEE 802 Series

Fiber UTP wireless cable

80211 8023

8022 LLC (Logic Link Control)

SMTP FTPHTTP

TCP UDP

SNMP DNS

IP

Ethernet802128024 8025

bull8023 CDMACD

bull8024 Token-bus

bull8025 Token-ring

bull80211 Wireless LAN

bull80212 100VG-AnyLAN

43

IEEE 8023 Protocol

Ethernet is compatible to 8023 Length of bytes in LLC

Preamble SourceDestination Length Data from LLC FCS

Bytes 8 6 6 2 46-1500 4

64-1518 bytes

44

Flow Chart of IEEE 8023傳送訊框

組成訊框

線上有訊號

訊框過短( )衝撞

檢查碼正確

傳送訊框

發生衝撞

傳送完畢

jamming送出signal

i=i+1

i gt 16

計算延遲時間

等待延遲時間

傳送失敗傳送成功

Y es

No

No

No

Y es

Y es Y es

No

接收訊框

開始接收

接收完畢

位址辨識成功

尚有多餘位元

刪除訊框頭尾

長度錯誤對齊錯誤

Y es

No

No

No

Y es

Y es

Y es

接收成功訊框錯誤

長度欄位內容正確

No

Y es No

Y es

No

Page 40: 1 Introduction of Ethernet Metcalfe’s Ethernet sketch Also refer to nfhuang/chap04.htm

40

Properties of An Ethernet

Shared bus technology( broadcast) Lowest level hardware does not support

addressing Best-effort delivery mechanism No central authority to grant access Each transmission is limited in duration

41

Part 4

IEEE 8023

42

IEEE 802 Series

Fiber UTP wireless cable

80211 8023

8022 LLC (Logic Link Control)

SMTP FTPHTTP

TCP UDP

SNMP DNS

IP

Ethernet802128024 8025

bull8023 CDMACD

bull8024 Token-bus

bull8025 Token-ring

bull80211 Wireless LAN

bull80212 100VG-AnyLAN

43

IEEE 8023 Protocol

Ethernet is compatible to 8023 Length of bytes in LLC

Preamble SourceDestination Length Data from LLC FCS

Bytes 8 6 6 2 46-1500 4

64-1518 bytes

44

Flow Chart of IEEE 8023傳送訊框

組成訊框

線上有訊號

訊框過短( )衝撞

檢查碼正確

傳送訊框

發生衝撞

傳送完畢

jamming送出signal

i=i+1

i gt 16

計算延遲時間

等待延遲時間

傳送失敗傳送成功

Y es

No

No

No

Y es

Y es Y es

No

接收訊框

開始接收

接收完畢

位址辨識成功

尚有多餘位元

刪除訊框頭尾

長度錯誤對齊錯誤

Y es

No

No

No

Y es

Y es

Y es

接收成功訊框錯誤

長度欄位內容正確

No

Y es No

Y es

No

Page 41: 1 Introduction of Ethernet Metcalfe’s Ethernet sketch Also refer to nfhuang/chap04.htm

41

Part 4

IEEE 8023

42

IEEE 802 Series

Fiber UTP wireless cable

80211 8023

8022 LLC (Logic Link Control)

SMTP FTPHTTP

TCP UDP

SNMP DNS

IP

Ethernet802128024 8025

bull8023 CDMACD

bull8024 Token-bus

bull8025 Token-ring

bull80211 Wireless LAN

bull80212 100VG-AnyLAN

43

IEEE 8023 Protocol

Ethernet is compatible to 8023 Length of bytes in LLC

Preamble SourceDestination Length Data from LLC FCS

Bytes 8 6 6 2 46-1500 4

64-1518 bytes

44

Flow Chart of IEEE 8023傳送訊框

組成訊框

線上有訊號

訊框過短( )衝撞

檢查碼正確

傳送訊框

發生衝撞

傳送完畢

jamming送出signal

i=i+1

i gt 16

計算延遲時間

等待延遲時間

傳送失敗傳送成功

Y es

No

No

No

Y es

Y es Y es

No

接收訊框

開始接收

接收完畢

位址辨識成功

尚有多餘位元

刪除訊框頭尾

長度錯誤對齊錯誤

Y es

No

No

No

Y es

Y es

Y es

接收成功訊框錯誤

長度欄位內容正確

No

Y es No

Y es

No

Page 42: 1 Introduction of Ethernet Metcalfe’s Ethernet sketch Also refer to nfhuang/chap04.htm

42

IEEE 802 Series

Fiber UTP wireless cable

80211 8023

8022 LLC (Logic Link Control)

SMTP FTPHTTP

TCP UDP

SNMP DNS

IP

Ethernet802128024 8025

bull8023 CDMACD

bull8024 Token-bus

bull8025 Token-ring

bull80211 Wireless LAN

bull80212 100VG-AnyLAN

43

IEEE 8023 Protocol

Ethernet is compatible to 8023 Length of bytes in LLC

Preamble SourceDestination Length Data from LLC FCS

Bytes 8 6 6 2 46-1500 4

64-1518 bytes

44

Flow Chart of IEEE 8023傳送訊框

組成訊框

線上有訊號

訊框過短( )衝撞

檢查碼正確

傳送訊框

發生衝撞

傳送完畢

jamming送出signal

i=i+1

i gt 16

計算延遲時間

等待延遲時間

傳送失敗傳送成功

Y es

No

No

No

Y es

Y es Y es

No

接收訊框

開始接收

接收完畢

位址辨識成功

尚有多餘位元

刪除訊框頭尾

長度錯誤對齊錯誤

Y es

No

No

No

Y es

Y es

Y es

接收成功訊框錯誤

長度欄位內容正確

No

Y es No

Y es

No

Page 43: 1 Introduction of Ethernet Metcalfe’s Ethernet sketch Also refer to nfhuang/chap04.htm

43

IEEE 8023 Protocol

Ethernet is compatible to 8023 Length of bytes in LLC

Preamble SourceDestination Length Data from LLC FCS

Bytes 8 6 6 2 46-1500 4

64-1518 bytes

44

Flow Chart of IEEE 8023傳送訊框

組成訊框

線上有訊號

訊框過短( )衝撞

檢查碼正確

傳送訊框

發生衝撞

傳送完畢

jamming送出signal

i=i+1

i gt 16

計算延遲時間

等待延遲時間

傳送失敗傳送成功

Y es

No

No

No

Y es

Y es Y es

No

接收訊框

開始接收

接收完畢

位址辨識成功

尚有多餘位元

刪除訊框頭尾

長度錯誤對齊錯誤

Y es

No

No

No

Y es

Y es

Y es

接收成功訊框錯誤

長度欄位內容正確

No

Y es No

Y es

No

Page 44: 1 Introduction of Ethernet Metcalfe’s Ethernet sketch Also refer to nfhuang/chap04.htm

44

Flow Chart of IEEE 8023傳送訊框

組成訊框

線上有訊號

訊框過短( )衝撞

檢查碼正確

傳送訊框

發生衝撞

傳送完畢

jamming送出signal

i=i+1

i gt 16

計算延遲時間

等待延遲時間

傳送失敗傳送成功

Y es

No

No

No

Y es

Y es Y es

No

接收訊框

開始接收

接收完畢

位址辨識成功

尚有多餘位元

刪除訊框頭尾

長度錯誤對齊錯誤

Y es

No

No

No

Y es

Y es

Y es

接收成功訊框錯誤

長度欄位內容正確

No

Y es No

Y es

No