Packet Switching

Switching: - Switching is the technique of transferring the data from one place to another place or from one network to another network very fast and quickly.

There are three types of Switching:-

1.      Circuit Switching.

2.      Message Switching.

3.      Packet Switching.

·         Circuit Switching: - Circuit Switching is the Switching technique in which a dedicated channel or circuit is established between two nodes for the transfer of data.

·         Message Switching: - Message switching is the technique of switching in which data is transferred in the form of messages. Each message is treated as a separate entity and the data is transferred through different routers.

·         Packet Switching: - Packet switching is the technique of switching which is used to transfer the data on a local or long distance. In packet switching data is divided into small packets for transmission. Each data packet carries a header which stores the destination address in it. When the packets reach to the destination they again from the complete message in the similar from it was before transmission.

A packet comprises of:-

ž  Source: - The IP address of the computer sending the packet.

ž  Destination: - The IP address of the destination computer.

ž  Length: - The length of the packet in bytes.

ž  Number: - The total number of packets in the complete message.

ž  Sequence: - The number of this packet in the whole list of packets making up this communication.

Sometimes it happens that the packets of message do not reach the destination because of the congestion in the network. In this case when lots of message will be missed there will be many junk files in the network which will block the network. To avoid these Hop packets is used along with the message packets.

Hop packets: - Hop packets are the packets in which a fixed number is defined for every packet and within that number only the packet must reach the destination and if it doesn’t happen the packet will be deleted by its own. Every packet the message will pass the hop number will be decreased. 

Advantages of Packet Switching:-

ž  It makes very efficient use of the network - no tied-up lines.

ž  It can easily get around broken bits of the network.

ž   As customers increase, the network only has to expand slowly compared
 to circuit switching.

Disadvantages of Packet Switching:-

ž  The time it takes to put back the data package changes each time, which can be a problem for time-critical information such as an emergency signal. The fancy name is for this is 'latency'.

ž  Not very good for small data packages - for example if the data package itself is only 600 bytes long, then two packets of 512 bytes need to  be used, plus the address information.

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