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In the previous tutorials, we have studied about the access control methods, error control methods. Now, we move ahead to learn about switching. We will learn about what is switching, types of switching (circuit and packet switching). Finally, we will see comparison between different types of switching (circuit and packet switching).
The process of forwarding the incoming packet from one port to another suitable port is called Switching.
Examples of Switching
- Several junctions in the communication path perform movement of data from one network to another whenever we place a call.
- Gateway used by Internet Service Providers (ISP) to deliver a signal to another Internet Service Providers (ISP) is another example of switching
Types of switching:
Practically, switching can be of two types –
- Circuit switching
- Packet switching
1. Circuit Switching
It is a real-time connection-oriented system. A dedicated channel (or circuit) is set up for a single connection between the sender and the recipient during the communication. In a telephone communication system, the normal voice call is the example of Circuit Switching. The telephone service provider maintains an unbroken link for each telephone call.
There are 3 phases in circuit switching:
- Connection establishment
- Data transfer
- Connection release
- Since a connection is established, resources are reserved in circuit switching.
- Transmission is done only by the source.
- Source calculates the best possible path for the data to be transferred from source to the destination. Thus, each packet contains the entire path address.
- In circuit switching, delay between the data units is uniform.
2. Packet Switching
The most common example of Packet Switching is the Internet. In this type of switching, data can be fragmented into suitably-sized pieces of variable length or blocks called packets. The packets can be routed independently by network devices based on the destination address containing certain “formatted” header within each packet. The packet switched networks allow sending and receiving data without reserving the circuit. Multiple paths may exist between sender and receiver in a packet switching network.
Some of the points to remember for packet switching are:
- Here, data is transferred directly without any connection establishment.
- Since there is no connection establishment, data can be transmitted by both the source and the routers. Hence, no reservation of resources is required.
- Each packet contains only the destination address. Thus, the intermediate packet path is decided by the routers.
- The routers store the packets. Then, calculate the next best possible path. Thus, it is said to use the store and forward technique.
Comparison between Circuit Switching and Packet Switching
|Circuit Switching||Packet Switching|
|1. Connection is established to transfer information.||1. No connection is established to transfer information.|
|2. Transmission is done by source.||2. Transmission is done by source and routers.|
|3. Each packet has entire path address.||3. Each packet has path address of next location only.|
|4. Not a store and forward technique.||4. Store and forward technique.|
|5. Uniform delay between the data units.||5. Non-uniform delay between the data units.|
|6. Resource reservation is done.||6. No resource reservation is done.|
|7. No congestion is possible.||7. Congestion is possible.|
|8. Wastage of resources.||8. No wastage of resources.|
|9. Not fault tolerant.||9. Fault tolerant.|
|10. Reliable data transfer.||10. Data transfer is not reliable.|
Which is better?
This completely depends upon the requirements. If we need a secured connection and the cost is not an issue, we prefer circuit switching. But, if we need to minimise the cost and reliability is not an issue, we opt for packet switching.
Can both be merged together (Circuit and Packet Switching)?
A new technology called ATM, attempts to combine the best of both worlds – the guaranteed delivery of circuit-switched network and efficiency and robustness of packet – switching network.
Hope, the idea of circuit and packet switching is clear in this tutorial. Now, we will move ahead to know about the various topologies in the next tutorial. Stay tuned for more tutorials ahead.