NETWORK SWITCH : Purpose and Functions

What are Network Switches?

A Network Switch is a constituent of computer network that connects two network slices and/or two network devices (switches or routers) together. Switch can be termed as a network bridge with multiple ports which helps to process and route packets at data link layer of the OSI reference model. There are some switches which have capabilities to process data at the upper layers (network layer and above). Those switches are often termed as multilayer switches.

Functions

The basic function that any switch is supposed to perform is to receive information from any source connected to it and dispatch that information to the appropriate destination only. This thing differentiates switches from hubs. Hub gets the information and forwards that to every other device in the network. This is the reason why switches are called intelligent devices.

The network switch has become a crucial part of present local area networks (LANs). LANs with medium to large sizes are established using a number of inter-linked network switches. SOHO (Small Office/Home office) networks generally consist of a single switch, or sometimes a multi-purpose device like a residential gateway to utilize small office/home broadband services such as Digital subscriber line (DSL) and cable Internet. Nowadays, we have been using router-like components which interface to the particular physical broadband technology. We may see some people using telephone technology on internet using Voice over IP (VoIP).

As mentioned above, a switch is operated at the data link layer to develop a distinct collision domain for each port of the switch. Let us consider, there are four computers - A, B, C, and D connected to four ports of the switch, then any pair , say A and B, may transfer data in either directions, at the same time, the other pair, C and D, can exchange their information simultaneously, and these two communications will not interrupt each other. Using full duplex mode, pairs may get overlapped (A communicating with B, B with C, and so on). Whereas in hubs, all of them have to share the same bandwidth by running in half duplex mode, causing collisions, which will result in unnecessary packet retransmissions.

Layer 2 Functionality

• Store and Forward: The switch stores and verifies each packet before routing it.
• Cut through: The switch verifies the portion of the packet header up to the hardware address of frame before it is forwarded. They may have to stick to the store and forward procedure if the outgoing port is engaged when the packet enters.
• Fragment free: It is the methodology that tries to preserve the advantages of both cut through and store and forward functionalities. Fragment free verifies the first 64 bytes of the packet, wherein addressing details are saved. This is because; collisions should be determined within the first 64 bytes of the packet frame, so erroneous packet frames will not be routed.
• Adaptive switching: This method automatically selects one of the above three methods depending upon traffic situation.