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.