A virtual circuit, abbreviated VC and also known as a virtual connection or virtual channel, provides a connection between points in a network in both telecommunications and computer networks. The virtual circuit allows packets of information to pass between the two connections. Typically, these circuits are used in networks with fast transfer speeds, such as asynchronous transfer mode (ATM) connections. While the virtual circuit may appear to be a physical path that connects two points in the network, it actually switches back and forth between various circuits to create different paths as needed.
When used in telecommunications, circuits carry signals along the path between the starting point and ending point. The network is simply a collection of various circuits, or paths, to connect all the different users to the network or other connection point. When referring to circuits in the context of electronics, such as use in a computer, the circuit still runs between two points but is more likely to connect more than two points to carry signals in the form of electrical currents. These circuits are permanent, whereas a virtual circuit can create different paths through a collection of various circuits and has no fixed, permanent path it must follow.
Two types of virtual circuits exist: permanent virtual circuits (PVC) and switched virtual circuits (SVC). As the names suggest, a PVC stays connected at all times while a SVC only connects when in use and disconnects afterward. Typically PVCs are used on frame relay networks, which connect local networks with wider area networks. A SVC can be used on frame relay networks but must maintain a constant connection during the transfer.
Virtual circuits can also be referred to as logical circuits, and it is important to keep in mind that while the circuit can change its path and connect to different networks or points, it still only connects two points at one time. It determines what two connections it needs to make and sets up the best path for a smooth and fast transfer. For this reason it appears to be a normal circuit connection that stays in place. The difference lies in how the circuit can choose two different points to create a new connection when necessary. This allows for fast transfers among various networks using fewer resources.
