Transport Layer in Computer Networks, Slides of Computer Networks

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Program Name :B.Tech

Semester :ECE 6th Sem

Course Name: Computer Network

Course Code:EC 602

Facilitator Name: Megha Dewan

Topic Name:- Transport Layer

Contents of Topic: Behrouz A. Forouzan Learning Outcome: Students get to know about basics of Transport Layer UNIT No. 1

What a Network layer actually does?

It oversees source-to-destination delivery of individual packets , it does not recognize any relationship between those packets. It treats each one independently , as though each piece belongs to a separate message.

How transport layer differ from network layer?

• (^) The transport layer , ensures that the whole message arrives intact and in order , overseeing both error control and flow control at the source –to-destination level.

Transport layer protocol

• (^) A transport layer protocol can be either connectionless or connection-oriented.
• (^) UDP-Connectionless protocol-Simple
• (^) TCP-Connection oriented protocol-Complex
• (^) SCTP-Connection oriented protocol-Designed for Multimedia application
• (^) (Stream control transport protocol)

PDU(SEGMENT)

• (^) In the Transport layer a message is normally

divided into transmittable segment.

• (^) UDP treats each segment separately
• (^) TCP creates a relationship between

the segments using sequence numbers.

Connection –oriented transport layer

• (^) A connection oriented transport layer makes a

connection with the transport layer at the

destination machine first before delivering the

packets.

• (^) After all the data is transferred , the

connection is terminated.

• (^) TCP and SCTP are Connection

oriented…

Reliable versus unreliable

Transport layer service can be reliable or unreliable

• (^) If the application layer program needs reliability, TCP &SCTP protocol will implement flow and error control at the transport layer. But it is slower and more complex service.
• (^) If the application layer program does not need reliability, it means most real-time application does not demand flow and error control,but it demand fast service. So unreliable protocol UDP is used.

Question arises?

• (^) If the data link layer is reliable and has flow

and error control , do we need this at

transport layer too?

Answer

YES

• (^) Reliability at the data link layer is between two nodes ;
• (^) we need reliability between two ends.
• (^) Because the network layer in the internet is unreliable.
• (^) So we need to implement reliability at the transport layer.

Addressing

• (^) At the Data link layer, we need a MAC address to choose ONE node among SEVERAL node.
• (^) At the Network layer we need an IP address to choose one Host among Millions.
• (^) At the Transport layer we need a transport layer address called a PORT NUMBER ,to choose among multiple processes running on the destination host.
• (^) Destination port number for delivery; source port no for the reply

Port number

• (^) Port number for a client host program defines

itself randomly by the transport layer. at this is

called ephemeral port number ranging from

49,152 to 65,

• (^) Port number for servers are universally

assigned by (internet assigned number

authority) called well-known port number

ranging from0 to 1023

Socket address

It is a 48 bit address. It is a combination of both IP Address and port number.

UDP

• (^) The User Datagram Protocol (UDP) is called a connectionless , unreliable transport protocol.
• (^) UDP is so powerless , it perform process to process communication with very limited error checking.
• (^) If a process wants to send a small message and does not care much about reliability , it can use UDP