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Sub-Topic : Features of TCP (Part-2)

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Recap

In the previous topic , you have learnt about

• Layers of TCP/IP protocol

• Role of transport layer in TCP/IP protocol

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Objectives

On completion of this topic, you would be able to know about

• List out the features supported by TCP

• Understand features of TCP

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TCP - Features

• Numbering System

• Byte Number

• Sequence Number

• Acknowledgement Number

• Reliable transfer of data

• Flow Control

• Error Control

• Congestion Control

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TCP – Features ( Contd…)

• Inter-operability

• Flexibility

• Multi-Vendor Support

• Window Based Protocol

• Connection oriented service

• Full duplex data transfer

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TCP – Numbering System

• TCP keeps track of the segments being transmitted or

received by assigning numbers

• Byte Number assigned to data bytes to be transferred

• Sequence Number to Segments

• Acknowledgement Number to Received segments

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Byte Number

• Used for Flow Control and Error Control

• All data bytes transmitted in each connection are numbered by the TCP

• Numbering starts with a randomly generated number

• Numbering is independent in each direction

• TCP stores the received data bytes in a sending buffer and numbers them

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Sequence Number

• TCP assigns a Sequence number to each segment transmitted

• Sequence Number is the first byte number carried in that segment

Sequence Number is assigned when• Segment carries both data and control information

( Piggy backing )

• Segment without data, no sequence number

• Example : if x Sequence Number x+1 First Byte Number

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Acknowledgement Number

• Indicates number of the next byte that the

receiver expects to receive

• Acknowledgement number is cumulative

• Confirmation to received data bytes

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TCP – Reliable Transfer of Data

• Ordered data transfer - the destination host rearranges according to sequence number

• Retransmission of lost packets - any cumulative stream not acknowledged will be retransmitted

• Discarding duplicate packets• Error-free data transfer

1111

HostClient

Send Packet 1Start Timer

Retransmit Packet1Start Timer

Packet should arrive ACK should be sent

ACK would normallyArrive at this time

Receive Packet 1Send ACK 1

Time Expires

Receive ACK 1Cancel Timer

Data PacketTimer

Timer

Fig.4

TCP – Reliable Transfer of Data

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TCP – Flow Control

• limits the rate a sender transfers data to guarantee reliable delivery

• The receiver continually hints the sender on how much data can be received (controlled by the sliding window)

• When the receiving host's buffer fills, the next acknowledgment contains a 0 in the window size, to stop transfer and allow the data in the buffer to be processed

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TCP – Error Control• TCP implements an error control mechanism for

reliable data transfer

• Error Control is byte – oriented

• Segments are checked for error detection

• Error Control includes detecting

• Corrupted Segments and Lost Segments

• Out-of-Order Segments

• Duplicated Segments

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• Error detection & Correction is achieved by

– Check Sum

– Acknowledgement Numbers

– Time-outs

TCP – Error Control

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TCP – Congestion Control

• TCP takes in to account the level of Congestion

in the network

• Congestion level determines the amount of

data sent by a sender

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TCP - Interoperability

• TCP has become the Industry standard

• It supports interoperability across networks

• TCP – A frame work used to develop• complete range of computer communication

standards

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TCP – Flexibility

• TCP allows a variety of implementations

Multi-Vendor Support

• TCP is supported by almost all network software

• Widely used transport layer protocol

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Summary

In this class, you have learnt about

• TCP is a widely used transport layer protocol

• TCP provides process to process, full duplex and connection oriented services

• The main features supported by TCP are

• Segment Numbering System

• Flow Control

• Error Control

• Congestion Control

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Summary

In this topic, you have learnt about

• Basic unit of data transfer using TCP is Segment

• TCP uses flow control implemented as a sliding window mechanism

• Data bytes being transferred in each connection are numbered by TCP

• Numbering starts with a randomly generated number

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Summary

TCP uses error control to provide reliable service. Error Control is handled by

• checksum, acknowledgement and time-outs

• Duplicated segments are discarded and Corrupted & lost segments are retransmitted

• Data arrived out of order are temporarily stored by receiving TCP

• TCP guarantees that no out of order segment is delivered to the process

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Quiz

1. TCP is a ____________ layer protocol

A. Application

B. Transport

C. Network

D. Physical

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Quiz

2. Which of the following features are supported by TCP ?

A. Congestion Control

B. Error Control

C. Flow Control

D. All The Above

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Frequently Asked Questions

1. Name the protocols used in the Transport Layer of the TCP/IP protocol suite

2. What is the purpose of TCP ?

3. List the features of TCP

4. Explain about the various features supported by TCP

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3.24            DIFFERENT LAYERS OF TCP/IP