Network Layer of the OSI Model
Network layer of the OSI Model
This is the third layer of the OSI model. The data unit at this layer is known as packet. There is no need of the network layer if the two communicating devices lie on the same network. However, when the two devices are connected on different networks, network layer is essential for providing source to destination delivery of packets.
Network layer receives data from transport layer. It adds header to the data and passes data to the data link layer. At the receiver side, network layer receives data from data link layer. It detaches header from the data and passes data to the transport layer.
Responsibilities of the network layer
The responsibilities of the network layer are:
Logical Addressing - The data link layer provides physical addressing which is useful for a local network. When the packet is destined for a device outside the network, we require other addressing scheme to identify source and destination. Network layer adds header to the data that includes the logical address (IP address) of the source and destination. It is a 32-bit address that uniquely identifies the device connected to the network.
Routing - Routing is a process wherein a proper path is defined for the packets to reach the destination. Routing can be of two types, static or dynamic. In static routing, the route to be followed by a packet is already set by the network administrator. In dynamic routing, the route to be followed by a packet is decided at the time of transmission of the packet. The route can be changed based on the available traffic on the network.
Handling Congestion Issues - Any given network has a certain capacity to deliver or handle number of packets. When the packets exceed the handling capacity, then the network is unable to cope with them and results in excess accumulation of packets over the network. This is called congestion. Congestion may occur due to various reasons like shortage of buffer space in network devices, slow links and slow processors. It is the responsibility of the network layer to control such congestion problems.
Internetworking - Internetworking means connecting two or more computer networks together. The Internet is the best example of internetworking. There are different types of networks that exist in the real world such as LAN, MAN and WAN. These networks are interconnected using various networking devices such as bridges, routers and gateways.
You may also be interested in understanding the other seven layers of the OSI Model