Thursday, May 20, 2010

OSI Model: Layers

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Network Layer


The network layer manages device addressing. It defines protocols for opening and maintaining network path between systems. It is also manages data transmission and switching procedures. Routers operate at the network layer. The network layer looks at packet addresses to determine routing methods. If a packet is for the system on the local network, it is sent directly there. If it is addressed to the system on another segment, the packet is sent to the router, which forwards it on the desired network.


Data-Link Layer


The data link layer provides the rules for sending and receiving information across the physical connection between two systems. This layer provides error detection and control. Because this layer provides error control, higher layers do not need to handle such services. Switches and Bridges operate at this layer.


Physical Layer


Physical layer sends and receives the bits. This layer defines the physical characteristics of the medium such as connectors, electrical characteristics such as voltage levels, and functional aspects such as setting up and maintaining the physical link. Well-known physical layer interfaces for local area networks (LANs) include Ethernet, Token-Ring, and Fiber Distributed Data Interface (FDDI). Hubs and Repeaters work at this layer.

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