Transport Layer

Sohag University

Computer Science

M.KARAM

17.11.2014

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Transport Layer Role and Services

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Transport Layer Role and Services cont.

The transport layer is concerned with the actual end-to-end transfer of the data across the network.

This layer establishes a logical connection between the two communicating hosts and provides reliable or unreliable data delivery and can provide flow control and error recovery.

The transport layer segments and reassembles data.

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Its Protocols

This layer have two protocols :

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Connection Types

1- Connection-oriented

In case of connection-oriented the hosts must establish connection before sending any data.It use TCP ( Transmission Control Protocol ) protocol.

2- Connectionless

In case of connectionless the hosts start sending data without establish connection.It use UDP ( User Datagram Protocol ) protocol.

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Connection-oriented

The connection will be connection-oriented if it have some conditions :

1- A virtual circuit is set up such as( A three-way handshake )

2- It uses acknowledgments 3- It uses sequencing4- It uses flow control

The connection that have this four conditions called “ A reliable connection “ .

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A virtual circuit

Before transmitting any segment of data the

sender's TCP process contacts the destination's

TCP process to establish the connection.

What is creates is known as “ a virtual circuit “ .

But how it was created ?

By using A three-way handshake

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A virtual circuit cont. (A three-way handshake)

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Acknowledgment

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Sequencing

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Flow control

Flow control is a function for the control of the data flow within an OSI layer or between adjacent layers. In other words it limits the amount of data transmitted by the sending transport entity to a level, or rate, that the receiver can manage.

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Windowing

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Connectionless

Connectionless using UDP Protocol.

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Connectionless cont.

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Port number

In computer networking, a port is an application-specific or process-specific software construct serving as a communications endpoint in a computer's host operating system.

The purpose of ports is to uniquely identify different applications or processes running on a single computer and thereby enable them to share a single physical connection to a packet-switched network like the Internet.

A port number is a 16-bit unsigned integer, thus ranging from 0 to 65535.

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Port number cont.

Well-known ports :

The port numbers in the range from 0 to 1023 are the well-known ports or system ports.They are used by system processes that provide widely used types of network services.

Examples :

23 → telnet22 → SSH (Secure Shell)80 → HTTP

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Transport Layer Header

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The role of port numbers

the role of port numbers in establishing TCP sessions and directing segments to server process.

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The role of port numbers cont.

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Thank you