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Virtual Circuits
Chapter 2, “Networking Standards,” introduces you to packet switching and other routing-related techniques used to send data over WAN links. Packet-switching networks often use virtual circuits to route data from the source to the destination. A virtual circuit is a specific path through the network—a chain of communication links leading from the source to the destination (as opposed to a scheme in which each packet finds its own path). Virtual circuits enable the network to provide better error checking and flow control.

A switched virtual circuit (SVC) is created for a specific communication session and then disappears after the session. The next time the computers communicate, a different virtual circuit might be used.

A permanent virtual circuit (PVC) is a permanent route through the network that is always available to the customer. With a PVC, charges are still billed on a per-use basis.