virtualcircuit

A virtual circuit is a communication pathway between two network endpoints established to carry data along a predefined route. It presents itself as a dedicated connection, while sharing the underlying physical network infrastructure.

In practice, virtual circuits are created by network equipment that maintains per-connection state and uses signaling to establish, maintain, and terminate the path. The approach is connection-oriented, in contrast to datagram networks. Virtual circuits were widely used in packet-switched networks such as X.25, Frame Relay, and ATM. In ATM, the concept is central; permanent virtual circuits (PVCs) and switched virtual circuits (SVCs) define permanent or on-demand connections. In Frame Relay, virtual circuits are called PVCs or switched virtual circuits. In older X.25 networks, virtual circuits provided reliable, orderly delivery.

Modern analogs include MPLS, where label-switched paths function as virtual circuits over IP networks. The network assigns resources and forwards packets based on the path label rather than the destination address, enabling quality of service and traffic engineering.

Advantages of virtual circuits include reduced per-packet overhead, potential for predictable performance, and easier enforcement of connection-oriented policies. Disadvantages include setup delay for on-demand circuits, state maintenance in network devices, and potential inefficiency if many short-lived circuits are created.

See also virtual circuit switching, MPLS, ATM, and Frame Relay for related concepts and implementations.