2.1 OSI Model


The International Organization for Standardization (ISO) and the CCITT (Consultative Committee on International Telephony and Telegraphy), which is now the ITU (International Telecommunications Union), worked on a reference model at the same time that DARPA was doing research in networking protocols. The effort resulted in the OSI (Open Systems Interconnection) model (ISO 7498), which defined a seven-layer model of data communication with the physical layer at the lowest layer and application protocols at the upper layer. This model has been widely accepted as the basis for the understanding and design of a network protocol stack. It is also the basis against which other networking protocols are compared. The OSI reference model has seven layers , as shown in Figure 2-1.

Figure 2-1. OSI reference model.

graphics/02fig01.gif

The functionality of the seven layers of the OSI model is as follows :

Application: The application layer supports user applications such as file transfer protocol, HTTP, and others.

Presentation: The formatting of data and encryption are performed by this layer.

Session: Manages the establishment and maintenance of sessions.

Transport: Provides the reliable and unreliable end-to-end data delivery protocols.

Network: Performs the packet delivery function and routing of packets in the network.

Data link: Performs the framing of units of information and error checking.

Physical: Does the transmission of bits on the physical hardware.



IP in Wireless Networks
IP in Wireless Networks
ISBN: 0130666483
EAN: 2147483647
Year: 2003
Pages: 164

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