Role of Transport Layer - Responsibilities and Protocols

Transport layer is the fourth layer in OSI Reference Model. It responds to service requests from Session layer and issues service requests to Network layer. Transport Layer is responsible for delivering messages between hosts. In Transport layer, data travels in the form of segments. Transport layer is responsible for creating an end to end connection between source IP and the destination IP. For establishing this end to end connection, Transport layer is using two major protocols TCP and UDP. TCP is connection oriented protocol where UDP is connection less protocol. So by using TCP we can create an end to end reliable connection between source and destination hosts. Transport layer is called host-to-host transport layer in TCP/IP model.


Duties of Transport layer


Major duties of Transport layer are:
  1. Creating an end-to-end connection between hosts in different network,
  2. Error recovery,
  3. Flow control,
  4. Ensuring complete data transfer in TCP
  5. Congestion avoidance


The end to end connection is established in Transport layer with the help of stateful protocol TCP. It offers reliable delivery of data to the destination host. Transport Layer is also responsible for error recovery and is responsible for the resending of data segments which had error. This feature is provided by TCP. Flow control is the process of ensuring where the amount of data sending to the destination is affordable by it. Without flow control a faster source might flood destination with so much information. To accomplish it we are using many techniques like windowing.

Major Transport Layer protocols



1. TCP( Transmission Control Protocol)

2. UDP( User Datagram Protocol)

3. DCCP (Datagram Congestion Control Protocol)

4. SCTP (Stream Control Transmission Protocol).



Suggested Readings
  1. Physical layer

  2. Data link layer

  3. Network layer

  4. Transport layer

  5. Session layer

  6. Presentation layer

  7. Application layer
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