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What does the network layer do? Where does it sit in relationship to the other four layers of our simplified network model? Network layer is the third layer of the OSI model. It performs switching and routing by creating logical paths, known as virtual circuits, for transferring data from one node to another node. Routing and forwarding are the major functions of this layer. It also performs other operations such as addressing, internetworking, error handling, congestion, control and packet sequencing. It maintains the quality of service requested by the transportation layer. It determines how data are transferred between network devices. It Routes packets according to unique network device addresses and Provides flow and congestion control to prevent network resource depletion. The network layer provides the functional and procedural means of transferring variable length data sequences from a source to a destination host via one or more networks while maintaining the quality of service and error control functions. At this layer, the computer system engages in a dialogue with the network to specify the destination address and to request certain network facilities, such as priority  Network Layer consists of three sub layers:

Sub network Access:
This layer considers protocols that deal with the interface to networks, such as X.25. Sub network Dependent Convergence:
This layer is necessary to bring the level of a transit network up to the level of networks on either side. Sub network Independent Convergence:
It handles transfer across multiple networks.

The major Functions of the network layer are:
Routing: 
The most outstanding function of network layer is routing which includes Moving data across a series of interconnected networks the network layer. At the network layer, the devices and software routines handles incoming packets from various sources, determines their final destination, and then transfers the data to their destination....
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