Network Layer - Computer Science

Network Layer

Purpose and features. The network layer serves to organize the joint operation of several networks with different architectures when they are combined into a single network, called composite network. The technology that allows such an integration is called interworking technology (Internetworking). A local network with one architecture (Ethernet, FDDI, Token Ring, ATM or Frame Relay) is not capable of providing data transmission to a network with a different architecture, which is caused by many reasons (different formats of used frames, protocol logic, etc.). Even more differences can be found between the architectures of local and global networks. Thus, for the organization and coordination of work in networks built on the basis of different architectures, additional funds are needed. Such tools provide a network layer in the form of protocols and special devices.

The network layer is responsible for delivering data packets from the sender of one network to the recipient of another network. Networks are interconnected by special devices called routers. The router collects information about the interconnection topology and, on its basis, forwards packets from the recipient network to the destination network. When transmitting packets, there are several transit transmissions between networks. The sequence of routers, or the path through which the packet passes, is called the route. Compiling (selecting, determining) the best path, or routing , is one of the main tasks of the network layer. Routing dramatically increases the efficiency of using physical channels, since packets of the same message can be delivered in different ways, although network users do not notice it. At the network level, most routing protocols work.

Features of the work. The entire path of the transmitted message through the composite network is divided into sections from one router to another, each section corresponding to the path through a separate network. The data arriving at the network layer (from the overlying transport) is supplied with a network layer header. The collection of data and header forms an package. The header of the package has a unified format and contains its destination address. Within this composite network, each node has its own unique address, which is called the network address of the node. Along with this address on the underlying channel level, each node is assigned an hardware MAC address, e. The nodes of the composite network have two addresses. The packet route is determined based on the destination address specified in the packet at the network layer and is described by the sequence of routers (or networks) through which the packet must pass. The router extracts the packet from the incoming frame and, after processing, transmits the packet to the next network, having pre-packed it into the frame of the link layer corresponding to the format of this network.

Network-level devices: These include network-level routers and switches. One of the functions of the router is the physical connection of networks. Therefore, the router has several network interfaces, which can be considered nodes of different networks. One network is connected to each interface. Routers are built on the basis of specialized hardware platforms. Their software includes network-level protocol modules. The router can be implemented programmatically on the basis of a universal computer.

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