Editing Virtual circuit (section)

==Permanent and switched virtual circuits in ATM, Frame Relay, and X.25==
'''Switched virtual circuits''' ('''SVCs''') are generally set up on a per-[[telephone call|call]]  basis and are disconnected when the call is terminated; however, a  '''permanent virtual circuit''' ('''PVC''') can be established as an option to provide a [[dedicated circuit]] [[data link|link]] between two facilities.  PVC configuration is usually preconfigured by the service provider.  Unlike SVCs, PVC are usually very seldom broken/disconnected.

A switched virtual circuit (SVC) is a virtual circuit that is dynamically established on demand and is torn down when transmission is complete, for example after a phone call or a file download. SVCs are used in situations where data transmission is sporadic and/or not always between the same data terminal equipment ([[Data terminal equipment|DTE]]) endpoints.

A permanent virtual circuit (PVC) is a virtual circuit established for repeated/continuous use between the same [[Data terminal equipment|DTE]]. In a PVC, the long-term association is identical to the data transfer phase of a [[virtual call]]. Permanent virtual circuits eliminate the need for repeated call set-up and [[Clearing (telecommunications)|clearing]].

* Frame Relay is typically used to provide PVCs.
* [[Asynchronous Transfer Mode|ATM]] provides both '''switched virtual connections''' and '''permanent virtual connections''', as they are called in ATM terminology.
* [[X.25]] provides both '''virtual calls''' and PVCs, although not all X.25 service providers or DTE implementations support PVCs as their use was much less common than SVCs