Transport layer provides the peer-to-peer communication and the communication between the process or the hosts.

Transport layer gets data from the upper layer of the model and then it breaks that data into small segments , then perform sequencing over the segments of data and then at last sends it to the lower layer for delivery.

End-to-End Communication

The process of one terminal or host identifies the peer terminal or host on the remote network by means of post numbers.

FUNCTIONS OF TRANSPORT LAYER:

• Service Point Addressing :  The Transport layer will provide the address to the service point termed as the port address to the network.

• Segmentation and Reassembling : The message in this layer is divided into segments which contains the sequence number for every message through which we can also reassemble if we want.

• Connection Control : It includes 2 types :
  • Connectionless Transport Layer :The packet in this layer is considered in the form of segment and gets delivered to the transport layer at the destination point.
  • Connection Oriented Transport Layer : Before making delivery of the packets in the  network , connection should be established at the destination point.

• Flow Control : In this layer, flow control is performed end to end.

• Error Control : Error control mechanism is done by this layer to ensure that the full message gets received at the destination point. If in any case any error occur then retransmission is done

The two main Transport layer protocols are:

• Transmission Control Protocol

  It provides reliable communication between two hosts.

• User Datagram Protocol

  It provides unreliable communication between two hosts.