Overview of the Transport  Layer Protocols

Transport layer  can be  available  more than  protocols  to the  network  applications. For  example the network  applications. For  example  to internet  has two  protocols.

a.UDP ( User Datagram Protocol)

b.TCP ( Transmission Control Protocol)

UDP which  provides an  unreliable connectionless service to the  invoking application and TCP which  provides  a reliable connection oriented service to the invoking application when  designing a network  application the application developer must  specify one of  these two transport  protocols.

Before  proceeding to the  brief study  of UDP and TCP it will  useful to understand about  internet  in network layer. The internet  network  layer protocols  has a name IP for  internet protocol. IP provides  logical  communication  between  hosts. The IP service  model  is a  best effort delivery service.

This  means  that IP  make its best effort  to deliver  segments  between  communication hosts but it makes  no guarantees for  segment delivery and orderly delivery and orderly delivery of segments it does not guarantee the integrity  of the data in the segments too so that IP is said  to be an  unreliable  service. Every  host at least  one network  layer address it is called IP address.

The most fundamental responsibility  of UDP and TCP is to extent IP delivery service between  two end  systems to   a delivery service between  two processes running  on the end  systems. Extending host to  host delivery to process to process delivery  is called transport layer multiplexing and demulitplexing. UDP and TCP also provides  integrity checking by  including error detection fields in their segments header. These two  transport layer services process to process data  delivery  and error checking are the only  two services  the UDP provides  like IP. UDP is an unreliable service it does  not guarantee that data  sent by  one process will  arrive intact to the destination process.

TCP on the  other hand  provides reliable data  transfer using flow  control sequence number  acknowledgements  and  timers. TCP ensures that data  is delivered from  sending process to receiving  process correctly and in order. TCP converts IP unreliable service between  end system into a reliable data transport   service between processor. TCP also   provides  congestion control. It prevents any one TCP connection from swamping the links  and switches between  communicating hosts with an excessive amount  of traffic. In  principle  TCP permits TCP connections  traversing a congested network link to  equally share that links  bandwidth. This is done by regulating the rate at which  the sending  side TCP can send  traffic  into the network . UDP traffic on the other hand is unregulated. An  application using DUP transport can  send at any rate it suites of r as long as it pleases.