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Baûn quyeàn ®2004- Khoa Coâng Ngheä Thoâng Tin Trang 1

Tröôøng Ñaïi Hoïc Baùch Khoa Tp.HCM

CHÖÔNG IV

LÔÙP NETWORK


Baûn u eàn ®2004- Khoa Coân N he Thoân Tin Tran 2

LÔÙP NETWORK

Muïc tieâu thieát keá lôùp network :– Lieân maïng:

Autonomous domain (subnet). Söû duïng caùch ñaùnh ñòa chæ maïng coù tính toaøn cuïc. Ñònh tuyeán. Söû duïng nhieàu kyõ thuaät lieân keát (LAN, WAN).

– Ñònh tuyeán trong lieân maïng.– Giaûi quyeát taéc ngheõn.

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LÔÙP NETWORK

Thieát bò söû duïng :

– Chuyeân duïng vaø duøng vaøo muïc ñích ñaëc bieät.– Laøm vieäc ñöôïc vôùi caùc kyõ thuaät LAN hay WAN.

– Ñöôïc bieát döôùi teân laø router hay ñoâi khi coøn goïi laøgateway.

•router



LÔÙP NETWORK

Toå chöùc beân trong cuûa lôùp network :– Virtual circuit

Caàu noái ñöôïc thieát laäp nhö laø ñöôøng ñi cuûa packet. Taát caùc caùc döõ lieäu truyeàn qua caàu noái.

Caàu noái ñoùng thì virtual circuit seõ ñoùng.

– Datagram

Packet ñöôïc tìm ñöôøng ñoäc laäp.

Töøng datagram chöùa ñöïng ñaày ñuû caùc ñòa chæ.

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LÔÙP NETWORK

Ví duï veà IP (Internet Protocol)

– RFC 791– Giao thöùc lôùp 3 phoå bieán.

– Giao thöùc neàn taûng taïo neân Internet.

– Connectionless.

Ví duï veà ñòa chæ IP– Ñoäc laäp vôùi ñòa chæ phaàn cöùng (MAC).

– Ñöôïc duøng cho nhöõng giao thöùc lôùp cao hôn vaø caùc öùngduïng maïng.



LÔÙP NETWORK

Ví duï veà ñòa chæ IPv4– Ñöôïc duøng cho vaán ñeà truyeàn thoâng lieân maïng.

– Ñöôïc gaùn treân moãi giao tieáp maïng. Moät ñòa chæ IP töông öùng moät keát noái giöõa moät maùy tính vaø

maïng.

Moät maùy tính coù nhieàu giao tieáp maïng töông öùng seõ coù moãi ñòachæ IP treân moãi giao tieáp maïng.

– Coù chieàu daøi 32 bit vaø chia thaønh hai phaàn: prefix chæ ñònh maïng (do global authority gaùn)

suffix chæ ñònh maùy tính treân moãi giao tieáp (do Localadministrator gaùn).

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LÔÙP NETWORK

•Moâ hình ñaùnh ñòa chæ IP trong maïng



LÔÙP NETWORK

Ví duï veà dònh daïng cuûa Packet (IP Datagram)

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LÔÙP NETWORK

Ví duï vaán ñeà veà truyeàn nhaän IP Datagram

– Khoâng höôùng keát noái (connectionless), töùc coù thay ñoåiñöôøng ñi.

– Coù theå ñöôïc trì hoaõn vaø truyeàn khoâng theo thöù töï.

– Coù theå bò maát trong khi truyeàn vì vaäy caàn taïo baûn sao.

Ví duï veà ñònh tuyeán treân IP– Ñöôïc dieãn taû taïi caùc router.

–

Chuyeån tieáp cô baûn döïa treân hop-by -hop.– Ñòa chæ ñích ñöôïc duøng cho vieäc xaùc ñònh ñöôøng ñi.



LÔÙP NETWORK

Ví duï veà vieäc ñònh tuyeán– Xaùc ñònh ñòa chæ ñích D.

– Tìm ñöôøng ñi ñeán D trong baûng ñöôøng ñi.

– Tìm ra ñòa chæ gôûi keá tieáp (Next hop address).

– Gôûi Frame ñeán N.

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LÔÙP NETWORK

140.192.10.5

0060CA23BE45

140.192.10.25

0060CA34CD29

140.192.100.34

0060CA4AD2EE

140.192.100.8

0060CAAABBCC

140.192.201.22

0060CA3499CC

140.192.201.126

0060CA3499DE

140.192.34.34

0060CA114499

140.192.34.35

0060CA7819AA

Router

140.192.201.1

00C0C1AA3410

140.192.10.1

00C0C1AA3411140.192.100.1

00C0C1AA3412

140.192.34.1

00C0C1AA3413

IP Routing



LÔÙP NETWORK

Laøm theá naøo ñeå chuyeån döõ lieäu giöõa caùc maïng– Döïa vaøo baûng ñöôøng ñi taïi boä ñònh tuyeán.

Network

140.192.10.0

140.192.100.0

Interface

0

1

140.192.201.0 2

140.192.34.0 3

Routing Table

Network.Host

140.192.10.5

140.192.10.25

Layer 2

0060CA23BE45

0060CA34CD29

140.192.100.34 0060CA4AD2EE

140.192.100.8 0060CAAABBCC

Layer 2 <--> Layer 3 TableARP Table

140.192.201.22 0060CA3499CC

140.192.201.126 0060CA3499DE

140.192.34.34 0060CA114499

140.192.34.35 0060CA7819AA

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LÔÙP NETWORKFrom 140.192.34.34 to 140.192.10.5

140.192.34.34 knows that 140.192.10.5 isn't on the same net and sends it to router at 140.192.34.1

Note DA for layer 2

Inside the router the Layer 2 headers and trailers are removed leaving only the

layer 3 packet.

The router looks up the packet's DA in the routing table and forwards to the

appropriate interface.

At the interface, layer 2 headers and trailers are added back.

DA is the address of the destination host.

SA is the address of the router.

FCS is recalculated.

00C0C1AA3413 IP 140.192.10.50060CA114499 Data FCS140.192.34.34

140.192.10.5 Data140.192.34.34

0060CA23BE45 IP 140.192.10.500C0C1AA3411 Data FCS140.192.34.34



LÔÙP NETWORK

ARP:– Address Resolution Protocol

– Phaân giaûi ñòa chæ IP thaønh ñòa chæ MAC.– Moãi node gôûi broadcast tìm moät node khaùc:

140.192.34.34 broadcasts tìm 140.192.34.1

– Node töông öùng traû lôøi vôùi ñòa chæ MAC cuûa noù 140.192.34.1 traû lôøi vôùi 00C0C1AA3412

Baûng ARP:– Bao goàm caùc tröôøng (IP, MAC) ñaõ ñöôïc hoïc töø caùc node laùng gieàng.

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LÔÙP NETWORK

Ví duï veà baûng ñöôøng ñi



LÔÙP NETWORK

Laøm theá naøo ñeå xaây döïng baûng ñöôøng ñi ?– Laøm baèng tay (Static Routing)

Baûng ñöôïc taïo baèng tay.

Thöôøng ñöôïc duøng trong caùc maïng nhoû.

Ñöôïc duøng neáu ñöôøng ñi khoâng bao giôø thay ñoåi.

– Töï ñoäng (Dynamic Routing) Phaàn meàm taïo vaø caäp nhaät thoâng tin trong baûng.

Caàn duøng trong caùc maïng lôùn.

Thay ñoåi ñöôøng ñi khi coù moät soá söï coá xaûy ra.

Ví duï: Distance Vector Routing, Link State Routing, HierarchicalRouting.

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LÔÙP NETWORK

Laøm theá naøo ñeå tìm ra ñöôøng ñi toát nhaát ?– Bieåu dieãn maïng döôùi daïng ñoà thò:

Node : bieåu dieãn cho router

Arc :bieåu dieãn communication line (link)

Ñaïi löôïng söû duïng:– Khoaûng caùch.

– Thôøi gian delay trung bình.

– Dung löïông.

– Söû duïng moät giaûi thuaät tìm ñöôøng Dijkstra.

Flooding, Flow-Based Routing.



LÔÙP NETWORK

A D1

2

6

G

4

(a )

F (¥, - ) D (¥,- )

A

B 7 C

2

H

33

2

2 FE

1

22

6

G

4

A

(c )

A

B (2 , A ) C (9 , B )

H (¥, - )

E (4 , B)

G (6 , A)

F (6, E) D (¥,- )A

(e )

A

B (2 , A ) C (9 , B )

H (9 , G)

E (4 , B)

G (5 , E)

F (6,E) D (¥,- )A

(f )

A

B (2 , A ) C (9 , B )

H (8 , F)

E (4 , B)

G (5 , E)

F (6, E) D (¥,1)A

(d )

A

B (2 , A ) C (9 , B )

H (¥, - )

E (4 , B)

G (5 , E)

F (¥, -) D (¥, -)A

H

E

G(b )

B (2 , A) C (¥, - )

H (¥, - )

E (¥, - )

G (6 , A)

•Moät ví duï tìm ñöôøng töø A->D duøng Dijkstra

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LÔÙP NETWORK

Giaûi thuaät Flooding :– Packet ñeán gôûi ra taát caû caùc link.

– Taïo moät löôïng lôùn packet truøng laëp.

– Caùc kyõ thuaät giaûi quyeát truøng laëp :

Duøng kyõ thuaät hop counter ñeå loaïi boû

Löu tröõ laïi packet ñaõ ñöôïc flood

– Selective flooding :

Router gôûi packet ra caùc link höôùng tôùi ñích.



LÔÙP NETWORK

Giaûi thuaät Flow-Based Routing :– Thuaät giaûi söû duïng taûi & moâ hình maïng (topology) cho tính toaùn vaø

choïn ñöôøng ñi toát nhaát (coù thôøi gian treå trung bình nhoû nhaát). Tính toaùn thôøi gian treã trung bình döïa treân taûi & topology.

Tính nhieàu laàn treân nhieàu taäp ñöôøng ñi.

Choïn ra taäp ñöôøng ñi toát nhaát.

Caùc thoâng tin ñeå tính toaùn thôøi gian treå trung bình: Moâ hình maïng.

Löu löôïng thoâng tin giöõa caùc node (router).

Dung löôïng ñöôøng truyeàn giöõa caùc node (router).

Taäp ñöôøng ñi ñang söû duïng.

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9

BA

4

CBA

1

DFBA

7

EA

4FEA

9AB

8

CB

3

DFB

2

EFB

4FB

4ABC

8

BC

3

DC

3

EC

2FEC

1ABFD

3

BFD

3

CD

3

ECD

4FD

7AE

2

BFE

3

CE

3

DCE

5FE

4AEF

4

BF

2

CEF

4

DF

5

EF

(b) The traffic in packets/sec and the routing matrix

A B C D E F

A

B

C

D

E

F

B C

E F

A D2020

20

50

20 10

1020

S o u r c e

Destination

(a) A subnet with linecapacibilities shown in kbps

LÔÙP NETWORK

Giaûi thuaät Flow-Based Routing :



LÔÙP NETWORK

Caùc coâng thöùc tính toaùn

– Ti= 1/(µCi - λi)– Wi= λI / Σ λi

– Taver = Ti x Wi

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LÔÙP NETWORK

Ví duï: (giaû söû 1/ µ = 800 bits/packet)

Line λ (pkts/sec) C(kbps) µC(pkts/sec) T(msec) Weight

AB 14 20 25 91 0.171

BC 12 20 25 77 0.146

CD 6 10 12.5 154 0.073

AE 11 20 25 71 0.134

EF 13 50 62.5 20 0.159

FD 8 10 12.5 222 0.098

BF 10 20 25 67 0.122

EC 8 20 25 59 0.098



LÔÙP NETWORK

Distance Vector Routing– Laø giaûi thuaät ñoäng (RIP,

RIPv2, IGRP)

– Coøn goïi laø Bellman-Ford,Ford-Fulkerson routing.

– Töøng router coù moät baûng chobieát con ñöôøng toát nhaát tôùiñích.

– Ñònh kyø trao ñoåi caùc baûngñöôøng ñi vôùi caùc router laùnggieàng.

– Tính toaùn laïi khi caùc lieân keát

coù loãi.

(a) Subnet

A B C D

E

I J K L

F GH

Router

0122540142318172192429

2436182772031200112233

2031198301960147229

2128362422403119221009

820282017301812100615

To A I H K

Newestimateddelay fromJ

JA JI JH JKdelay delaydelaydelayis is is is8 10 12 6

Newroutingtablefor J

Vectors received from

J's four neighbors(b) routing table

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LÔÙP NETWORK

Distance Vector Routing : (Tieáp theo)– Vaán ñeà Count-to-Infinity :

A B C D E

∞ ∞ ∞ ∞

∞ ∞ ∞

∞ ∞

∞

4

1

1

1

1

2

2

2

3

3

Initially

After 1 exchange

After 2 exchanges

After 3 exchanges

After 4 exchanges

A B C D E

1 2 3 4

∞ ∞ ∞ ∞

2 3 4

3 4

4

6

3

3

5

5

4

4

6

5

5

67 6 7

87 8 7

Initially

After 1 exchang

After 2 exchang

After 3 exchang

After 4 exchang

After 5 exchang

After 6 exchang...

(a)

(b)



LÔÙP NETWORK

Distance Vector Routing : (Tieáp theo)– Giaûi quyeát vaán ñeà Count-to-Infinity :

Hold down :– Chôø moät thôøi gian tröôùc khi thay ñoåi ñöôøng ñi. Baùo giaù trò voâ

cuøng cuûa moät router. Caên baûn döïa vaøo timer.

Report the entire path :– Baûo ñaûm khoâng bò laêp nhöng traû giaù khaù ñaét.

Split horizon :– Khoâng baùo caùc ñöôøng ñi ñeán caùc router laùng gieàng neáu höôùng ñi

ñoù khoâng nhaän ñöôïc töø caùc router laùng gieàng khaùc.

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LÔÙP NETWORK

Link State Routing :– OSPF

– Caùc router trao ñoåi thoâng tin traïng thaùi lieân keát.

– Caùch thöïc hieän : Tìm caùc neighbors & hoïc ñòa chæ cuûa noù :

– Duøng packet HELLO

Tính toaùn delay & chi phí cho töøng neighbors cuûa noù :– Duøng packet ECHO.

Xaây döïng packet duøng baùo taát caû ñaõ ñöôïc hoïc.

Gôûi packet naøy ñeán taát caû router : duøng flooding

Tính toaùn con ñöôøng ngaén nhaát tôùi moïi router khaùc.



LÔÙP NETWORK

Link State Routing : (Tieáp theo)– Xaây döïng Link State packet :

Packet bao goàm :– Sender

– Sequence number & age

– Danh saùch caùc neighbors

B C

E F

A D61

2

8

5 7

4 3

(a) A subnet

A

Seq.

Age

B C D E F

B 4

E 5

Seq.

Age

A 4

C 2

Seq.

Age

B 2

D 3

Seq.

Age

C 3

F 7

Seq.

Age

A 5

C 1

Seq.

Age

B 6

D 7

F 6 E 1 F 8 E 8

Link State Packets

(b) The link state packets for this subnet

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LÔÙP NETWORK

Hierarchical Routing :– Heä thoáng maïng lôùn -> baûng routing lôùn :

Hao toán nhieàu taøi nguyeân khi xöû lyù

Hao toán nhieàu bandwitdth ñeå truyeàn nhaän caùc report

– Router chia thaønh caùc vuøng (regions)

– Router bieát roõ veà vuøng cuûa mình & khoâng bieát caáu truùc caùc vuøng khaùc


LÔÙP NETWORK

Hierarchical Routing : (Tieáp theo)

Region 1 Region 2

Region 3 Region 5Region 4

1B

1A

1C

2A 2B

2C

5B 5C5A

5E5D

2D

4A

4B 4C

3A

3B

1B 1

1C 1

1B 2

1B 3

1B 3

1B 4

1C 3

1C 2

1C 3

1C 4

1C 4

1C 4

1C 5

1B 51C 6

Ð Ð1A

1C

2A

2B

2C

2D

3A

3B

4A

4B

4C

5A

5B

5C5D

1B

Line HopsDest.

Full table for 1A

1A

1C

2

3

4

5

1B

Line HopsDest.

Hierarchical table for 1A

1B 1

1C 1

1B 2

1C 2

1C 3

1C 4

Ð Ð

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