Virtual – circuit network is a category of packet switching network, where a virtual path is established between the source and the destination systems for data communication to occur. This path appears to the user as if it is a dedicated physical path, but actually is a logical circuit allocated from a managed pool of circuit resources as per traffic requirements. The network resources forming parts of this path can be shared by other communications, however, is not visible to this user.
Virtual – circuit switching is done at the network layer of the communication system.
In these networks, the path between the source and the destination nodes that is followed by first data packet gets allocated. All other data packets transmitted between them will use the same path.
All the resources like buffers and bandwidth get reserved before the transmission, and all data packets consume same resources.
Since all packets follow the same path, a common header and routing information is used by them.
They provide greater reliability and less complexity owing to fixed paths and fixed resources.
There are three phases of transmission by virtual circuits, set up, data transfer and teardown.
Set up Phase − In this phase, a virtual circuit or a route is established from the source to the destination through number of switches. The source and destination use global addresses using which the switches make routing table entries.
Data Transfer − Once the virtual circuit is set up, all packets follow the route established during the set up phase adhering to the routing tables.
Teardown Phase − When data transfer is complete, the source sends a teardown request. The destination responds using a teardown confirmation. The switches flush their routing table entries, thus relinquishing the circuit.
In the following diagram, we can that a virtual circuit is created, as denoted by the dotted lines, and all the packets from the sender to the receiver are being routed along this virtual circuit.