Transport Layer

The transport layer of the TCP/IP protocol suite contains two protocols: TCP and UDP. The first, the Transmission Control Protocol (TCP), is a reliable protocol that allows two application layers to converse with each other. It delivers a stream of characters from a source to a destination and vice versa. At the source it segments the stream bof bytes into manageable segments and delivers them, after adding the necessary header, to the IP for delivery. At the destination, it creates a stream of bytes from the received segments for the use f the application layer. The TCP protocol performance goes beyond that of the OSI transport layer protocol; it performs some of the tasks defined for the session layer in the OSI model. It creates a full-duplex connection between two application layers.

The second protocol, User Datagram Protocol (UDP), is just a very simple transport layer protocol that ignores even some of the duties of the transport layer as defined in the OSI model. It is an unreliable protocol that is used by applications that need fast delivery of single shot packets without worrying about flow and error control. However, UDP is sometimes a better choice for a transport layer protocol because it can support multicasting and broadcasting.