TCP and UDP

Transport Layer Protocols

The Transport layer is responsible for providing mechanisms for multiplexing upper-layer applications, establishing sessions, and tearing down virtual circuits. It also hides details of any network-dependent information from the higher layers by providing transparent data transfer.
The two most common Transport layer protocols of TCP/IP protocol suite are Transmission Control Protocol (TCP) and User Datagram Protocol (UDP). Both protocols manage the communication of multiple applications. The differences between the two are the specific functions that each protocol implements.

Flow Control

Data integrity is ensured at the Transport layer by maintaining flow control and by allowing
users to request reliable data transport between systems. Flow control prevents a sending host
on one side of the connection from overflowing the buffers in the receiving host—an event that
can result in lost data. Reliable data transport employs a connection-oriented communications
session between systems, and the protocols involved ensure that the following will be achieved:

• The segments delivered are acknowledged back to the sender upon their reception.
• Any segments not acknowledged are retransmitted.
• Segments are sequenced back into their proper order upon arrival at their destination.
• A manageable data flow is maintained in order to avoid congestion, overloading, and data loss.

The Transport layer provides for the segmentation of data and the control necessary to reassemble these pieces into the various communication streams. Its primary responsibilities to accomplish this are:

1. Tracking the individual communication between applications on the source and destination hosts
2. Segmenting data and managing each piece
3. Reassembling the segments into streams of application data
4. Identifying the different applications