A virtual circuit (VC) is established through the inclusion of virtual circuit identification data in packet headers. In contast to datagram transmissions, virtual circuit networks setup, reserve, maintain, and tear down specific pathway connections at the link layer and the physical layer. These circuits are described as virtual, because in contrast to dedicated or switched circuit networks, the underlying data model still involves packets. However, for virtual circuits, there is a control information channel of some sort used to manage the link layer.
When virtual circuits are set up and torn down for temporary transmissions, the resulting circuit is known as switched virtual circuit (SVC).
When virtual circuits are left in place for a relatively long time ("nailed up"), the resulting circuit is know as a permanent virtual circuit (PVC). Frame Relay is an example of data link protocol that uses PVCs.