Switching methods

Switching:

A network is a set of connected devices. Whenever we have multiple devices, we have the problem of how to connect them to make one to one communication possible. One solution is to make a point to point connection between each pair of devices (a mesh topology) of between a central device and every other device (star topology). These methods, however, are impractical and wasteful when applied to very large networks. A better solution is switching.

A switched network consists of a series of interlinked nodes, called switches. Switches are devices capable of creating temporary connections between two or more devices linked to the switch. In switched network, some of these nodes are connected to the end systems (computers ortelephones).

There are basically three types of switching methods are made available. Out of three methods, circuit switching and packet switching are commonly used but the message switching has been opposed out in the genera communication procedure but is still used in the networking application.

1) Circuit Switching

2) Packet Switching

3) Message Switching

Circuit Switching

Circuit Switching is generally used in the public networks. It comes into existence for handling voice traffic in addition to digital data. However digital data handling by the use of circuit switching methods are proved to be inefficient.

The end to end communication was established during the duration of call.· In circuit switching the routing decision is made when the path is set up across the given network. After the link has been sets in between the sender and the receiver then the information is forwarded continuously over the provided link.· In Circuit Switching a dedicated link/path is established across the sender and the receiver which is maintained for the entire duration of conversation.

Packet Switching

In Packet Switching, messages are broken up into packets and each of which includes a header with source, destination and intermediate node address information. Individual Packets in packet switching technique take different routes to reach their respective destination. Independent routing of packets is done in this case for following reasons:

1. Bandwidth is reduces by the splitting of data onto different routes for a busy circuit.

2. For a certain link in the network, the link goes down during transmission the remaining packet can be sent through another route.

Packet Switching Network

· The major advantage of Packet switching is that they are used for performing data rate conversion.

· When traversing the network switches, routers or the other network nodes then the packets are buffered in the queue, resulting in variable delay and throughput depending on the network’s capacity and the traffic load on network.

· Packet switching contrasts with another principal networking paradigm, circuit switching, a method which sets up a limited number of dedicated connections of constant bit rate and constant delay between nodes for exclusive use during the communication session.

· In cases where traffic fees are charged, for example in cellular

communication, packet switching is characterized by a fee per unit of

Information transmitted.

Message Switching

In case of Message Switching it is not necessary to establish a dedicated path in between any two communication devices. Here each message is treated as an independent unit and includes its own destination source address by its own. Each complete message is then transmitted from one device to another through internetwork.

Message Switching Data Network

· Each intermediate device receive the message and store it until the nest device is ready to receive it and then this message is forwarded to the next device. For this reason a message switching network is sometimes called as Store and Forward Switching.

· Message switches can be programmed with the information about the most efficient route as well as information regarding to the near switches that can be used for forwarding the present message to their required destination.

· The storing and Forwarding introduces the concept of delay. For this reasons this switching is not recommended for real time applications like voice and video arrival at the destination host is not the final objective of data communications on the Internet.