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Transport LayerTransport Layer

PART V PART V

Position of transport layer



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Transport layer duties

Chapters

Chapter 22 Process-to-Process Delivery

Chapter 23 Congestion Control and QoS



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Chapter 22

Process-to-Process Delivery:

UDP and TCP

22.122.1 ProcessProcess --toto --Process DeliveryProcess DeliveryClient-Server Paradigm

Addressing

Multiplexing and Demultiplexing

Connectionless/Connection-Oriented

Reliable/Unreliable



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The transport layer is responsible for process-to-process delivery.

NoteNote ::

Figure 22.1 Types of data deliveries



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Figure 22.2 Port numbers

Figure 22.3 IP addresses versus port numbers



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Figure 22.4 IANA ranges

Figure 22.5 Socket address



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Figure 22.6 Multiplexing and demultiplexing

Figure 22.7 Connection establishment



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Figure 22.8 Connection termination

Figure 22.9 Error control



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22.222.2 UDPUDP

Port Numbers

User Datagram

Applications

UDP is a connectionless, unreliable protocol that has no flow and error

control. It uses port numbers to multiplex data from the application

layer.

NoteNote ::



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Table 22.1Table 22.1 Well Well -- known ports used by UDP known ports used by UDP

Simple Network Management ProtocolSNMP161

Simple Network Management Protocol (trap)SNMP162

Trivial File Transfer ProtocolTFTP69

Remote Procedure CallRPC111

Network Time ProtocolNTP123

Domain Name ServiceNameserver53

Server port to download bootstrap informationBootps67

Client port to download bootstrap informationBootpc68

Returns the date and the timeDaytime13

Returns a quote of the dayQuote17

Returns a string of charactersChargen19

Active usersUsers11

Discards any datagram that is receivedDiscard9

Echo

Protocol

Echoes a received datagram back to the sender7

Description Port

Figure 22.10 User datagram format



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The calculation of checksum and itsinclusion in the user datagram are

optional.

NoteNote ::

UDP is a convenient transport-layer protocol for applications that provide flow and error control. It is also used

by multimedia applications.

NoteNote ::



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22.322.3 TCPTCP

Port Numbers Services Sequence Numbers Segments Connection Transition Diagram Flow and Error Control Silly Window Syndrome

Table 22.2Table 22.2 Well Well -- known ports used by TCP known ports used by TCP

Remote Procedure CallRPC111

FingerFinger79

Hypertext Transfer ProtocolHTTP80

Simple Mail Transfer ProtocolSMTP25

Domain Name ServerDNS53Bootstrap ProtocolBOOTP67

File Transfer Protocol (data connection)FTP, Data20

File Transfer Protocol (control connection)FTP, Control21

Terminal NetworkTELNET23

Returns the date and the timeDaytime13

Returns a quote of the dayQuote17

Returns a string of charactersChargen19

Active usersUsers11

Discards any datagram that is receivedDiscard9

Echo

Protocol

Echoes a received datagram back to the sender7

DescriptionPort



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Figure 22.11 Stream delivery

Figure 22.12 Sending and receiving buffers



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Figure 22.13 TCP segments

Example 1 Example 1

Imagine a TCP connection is transferring a file of 6000 bytes. Thefirst byte is numbered 10010. What are the sequence numbers foreach segment if data are sent in five segments with the first foursegments carrying 1000 bytes and the last segment carrying 2000bytes?



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The bytes of data being transferred ineach connection are numbered byTCP. The numbering starts with a

randomly generated number.

NoteNote ::

The value of the sequence number field in a segment defines the number of the first data byte contained in that

segment.

NoteNote ::



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The value of the acknowledgment field in a segment defines the number of

the next byte a party expects to receive.

The acknowledgment number is cumulative.

NoteNote ::

Figure 22.14 TCP segment format



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Figure 22.15 Control field

Table 22.3Table 22.3 Description of flags in the control field Description of flags in the control field

Terminate the connection.FIN

Synchronize sequence numbers during connection.SYN

The connection must be reset.RST

Push the data.PSH

The value of the acknowledgment field is valid.ACK

The value of the urgent pointer field is valid.URG

DescriptionFlag



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Figure 22.16 Three-step connection establishment

Figure 22.17 Four-step connection termination



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Table 22.4Table 22.4 States for TCPStates for TCP

The server is waiting for the application to close.CLOSE-WAIT

The server is waiting for the last acknowledgment.LAST-ACK

The other side has accepted the closing of the connection.FIN-WAIT-2

Waiting for retransmitted segments to die.TIME-WAIT

Connection is established.ESTABLISHED

The application has requested the closing of the connection.FIN-WAIT-1

A connection request is sent; waiting for acknowledgment.SYN-SENT

A connection request is received.SYN-RCVD

The server is waiting for calls from the client.LISTEN

There is no connection.

Description

CLOSED

State

Figure 22.18 State transition diagram



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A sliding window is used to make transmission more efficient as well as to control the flow of data so that the

destination does not become overwhelmed with data. TCP’s sliding

windows are byte-oriented.

NoteNote ::

Figure 22.19 Sender buffer



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Figure 22.20 Receiver window

Figure 22.21 Sender buffer and sender window



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Figure 22.22 Sliding the sender window

Figure 22.23 Expanding the sender window



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Figure 22.24 Shrinking the sender window

In TCP, the sender window size is totally controlled by the receiver

window value (the number of emptylocations in the receiver buffer).

However, the actual window size can be smaller if there is congestion in the

network.

NoteNote ::



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Some points about TCP’s sliding windows:

NoteNote ::

The source does not have to send a fullThe source does not have to send a fullwindow’s worth of data.window’s worth of data.

The size of the window can be increased orThe size of the window can be increased ordecreased by the destination.decreased by the destination.

The destination can send an acknowledgmentat any time.

Figure 22.25 Lost segment



Figure 22.26 Lost acknowledgment

Figure 22.27 TCP timers

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