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Showing posts from February 27, 2009

TCP/IP and the OSI Reference Model

As illustrated in Figure 1.2, the TCP/IP model consists of four layers, each of which can have several sublayers. These layers correlate roughly to layers in the OSI reference model and define similar functions. Some of the TCP/IP layers correspond directly with layers in the OSI reference model while other span several OSI layers. The four TCP/IP layers are: ... • The TCP/IP Application Layer refers to communications services to applications and is the interface between the network and the application. It is also responsible for presentation and controlling communication sessions. It spans the Application Layer, Presentation Layer and Session Layer of the OSI reference model. Examples include: HTTP, POP3, and SNMP. • The TCP/IP Transport Layer defines several functions, including the choice of protocols, error recovery and flow control. The transport layer may provide for retransmission, i.e., error recovery, and may use flow control to prevent unnecessary congestion by attempting to