Switching

SWITCHING

Whenever a number of computers are to be connected for data communication then they are to be connected through a switch. When the interacting computers are far enough then they can’t be connected directly or through a single switch. So switched network consisting of number of switches are interconnected to solve this.

Switching is the process through which a temporary connection can be made between two nodes connecting to a switch.

There are 3 types of switching technology like

1.    Circuit Switching

2.    Packet Switching

3.    Message Switching

1.    CIRCUIT SWITCHING:

· Here a dedicated path is established between two communicating nodes before actual data transfer begins.

· The path means connected sequence of physical links in which logical channel is dedicated to the connection.

·    Example- telephonic communication.

Phases of circuit switching---

There are 3 phases of circuit switching.

A.    Circuit Establishmentà

·       In circuit switching data transfer can’t start abruptly. Before data transfer begins a dedicated link is to be established.

·       At first the sender sends a request for connection to its attached switch. The switch depending on the destination address and condition of traffic routes the connection requests to the next switch. The process goes on until a switch is reached with which the node is to be connected directly.

·       If destination host is free to accept the request then it sends an acknowledgment signal to the sender following the same switched path which was established during connection request flow.

·       If the receiver is busy then it sends a busy signal to the transmitter following the same path.

·       Once the connection is established the path becomes transparent to the signal and no other device within the network can access the path until the connection is closed.

B.    Data Transferà

·       Once the connection is established, data can be transferred from sender to receiver.

·       Generally the connection is full duplex.

·       Data are exchanged in block and sent continuously.

C.    Circuit Disconnectà

The circuit may be disconnected by either end and the disconnection information is transferred from one end to another following the dedicated path.

Features Of Circuit Switching:

·       Circuit establishment requires some time and if a dedicated path is not established end to end then no data can be transferred.

Once the circuit is established the channel becomes transparent and data flow instantly without any delay.    

2.  PACKET SWITCHING:

·       In case of packet switching the sender breaks the whole message into a number og packets of suitable length and consisting sequential numbers.

·       No dedicated path is established between the two end parties prior to data communication.

·       The sender sends packets to the next node sequentially.

·       Each node after receiving the packet decides the next route for the packet.

·       All the packets are independent in nature and may traverse different paths to reach the destination.
Packet may reach the destination in a jumbled fashion.
 It is responsibility of receiver to rearrange the packets according to their sequence number.

3.  MESSAGE SWITCHING:

•      Message switching is a combination of circuit switching and packet switching.
•        Like circuit switching the message is not broken into packets and like packet switching no dedicated path is established between the two end parties prior to data communication.