Virtual - Circuit Network

A Virtual-Circuit Network is a category of packet switching network where a virtual path is established between the source and destination systems for data communication. This path appears to the user as if it is a dedicated physical path, but is actually a logical circuit allocated from a managed pool of circuit resources based on traffic requirements. The network resources forming parts of this path can be shared by other communications, however this sharing is not visible to the user.

Features of Virtual-Circuit Network

• Network layer switching − Virtual-circuit switching is performed at the network layer of the communication system.

• Fixed path allocation − The path between source and destination nodes followed by the first data packet gets allocated. All subsequent data packets transmitted between them will use the same path.

• Resource reservation − All resources like buffers and bandwidth get reserved before transmission begins, and all data packets consume the same allocated resources.

• Common routing information − Since all packets follow the same path, a common header and routing information is used by them, reducing processing overhead.

• Enhanced reliability − They provide greater reliability and reduced complexity owing to fixed paths and dedicated resources.

Phases of Virtual-Circuit Transmission

Virtual-circuit transmission operates in three distinct phases: setup, data transfer, and teardown.

• Setup Phase − A virtual circuit or route is established from the source to the destination through a number of intermediate switches. The source and destination use global addresses, enabling switches to make routing table entries and reserve necessary resources.

• Data Transfer Phase − Once the virtual circuit is established, all packets follow the predetermined route created during the setup phase, adhering to the routing tables maintained by each switch along the path.

• Teardown Phase − When data transfer is complete, the source sends a teardown request to release the circuit. The destination responds with a teardown confirmation, and all switches flush their routing table entries, thus relinquishing the allocated circuit resources.

Virtual-Circuit vs Datagram Networks

Conclusion

Virtual-circuit networks provide a connection-oriented packet switching service by establishing dedicated logical paths between communicating nodes. They offer reliability and predictable performance through resource reservation, making them suitable for applications requiring guaranteed service quality.