In this a single route is choose between sender and receive at the beginning of the session.When the data are sent , all packets of the transmission travel one after another along that route.
Today virtual circuit transmission is implemented in two formats:
✔ Switched Virtual Circuit (SVC)
✔ Permanent Virtual Circuit (PVC)
1. Switched Virtual Circuit (SVC):
The switched virtual circuit (SVC) format is comparable conceptually to dial-up lines in circuit switching.
In this method a virtual circuit is made whenever it is needed and exist upto duration of message transmission.
Example:
Suppose A wants to send four packet to station (X). First a A request is establish connection to X. Once the connection is establish the packet are send one after another and in sequential order.
When the last packed has been received and if necessary acknowledged , the connection is released and virtual circuit causes to exist. Only one single path will exist for duration of transmission.
2. Permanent Virtual Circuit (PVC):
PVC is comparable to leased line in circuit switching. In this method , the same virtual circuit is provided between two user on a continues basis.The circuit is dedicated to the specific user. No one can else use it.It can be used without connection establishment and connection termination.When as one SVC user may get a different route , every time they request for connection , two PVC user always get the same route.
Note:
In virtual switching when we want to establish a connection than we first send Connection Request Packet (CR) which contain :
When route is create between two points than create an entry in Routing Table Such as:
The above figure explain the communication between A to B .When A will send packet to B , It will send Connection Request (CR) packet to B for establishing connection.In this case each router maintain Routing Decision Table which contain four fields.
Than B will send packet connection Confirm (CC) packet for confirming B is ready to receive data or packet to A.
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