▪︎Switching is process to forward packets coming in from one port to a port leading towards the destination.
▪︎When data comes on a port it is called ingress, and when data leaves a port or goes out it is called egress. A communication system may include number of switches and nodes.
▪︎At broad level, switching can be divided into two major categories
Connectionless: The data is forwarded on behalf of forwarding tables. No previous handshaking is required and acknowledgements are optional.
Connection Oriented: Before switching data to be forwarded to destination, there is a need to pre-establish circuit.
Types of Switching Techniques:
1)Circuit Switching
▪︎Circuit Switching is generally used in the public networks.
▪︎It come into existence for handling voice traffic in addition to digital data. How ever digital data handling by the use of circuit switching methods are proved to be inefficient.
▪︎In Circuit Switching a dedicated link/path is established across the sender and the receiver which is maintained for the entire duration of conversation.
▪︎In circuit switching the routing decision is made when the path is set up across the given network.
Advantages:
▪︎Data is transmitted with a fixed data rate.
▪︎No waiting time at switches.
▪︎Suitable for long continuous communication.
Disadvantages:
▪︎Resources are not utilized fully.
▪︎The time required to establish the physical link between the two stations is too long.
2)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
▪︎The major advantage of Packet switching is that they they are used for performing data rate conversion.
▪︎In cases where traffic fees are charged, for example in cellular communication, packet switching is characterized by a fee per unit of information transmitted.
Advantages:
▪︎It delivers the data to a destination by finding their own paths; circuit switching has a dedicated and predefined channel.
▪︎It is highly reliable as missing packets are detected by destination; circuit switching does not have this option.
Disadvantages:
▪︎This switching needs additional and secure protocols to protect the data, leading to a significant rise in implementation costs.
▪︎Packets don’t move in an organized way, sequence numbers should be provided to identify each packet.
3)Message Switching
▪︎In case of Message Switching it is not necessary to established 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 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.
Advantages:
▪︎It supports message lengths of unlimited size.
▪︎It does not require physical connection between source and destination devices unlike circuit switching.
Disadvantages:
▪︎This switching type is not compatible for interactive applications such as voice and video. This is due to longer message delivery time.
▪︎The method is costly as store and forward devices are expensive.
