Editing Virtual circuit (section)

==Example protocols==
Examples of transport layer protocols that provide a virtual circuit:
* [[Transmission Control Protocol]] (TCP), where a reliable virtual circuit is established on top of the underlying unreliable and connectionless IP protocol. The virtual circuit is identified by the source and destination [[network socket]] address pair, i.e. the sender and receiver IP address and port number. Guaranteed QoS is not provided.
* [[Stream Control Transmission Protocol]] (SCTP), where a virtual circuit is established on top of the IP protocol.
Examples of network-layer and data-link-layer virtual circuit protocols, where data always is delivered over the same path:
* [[X.25]], where the VC is identified by a [[virtual channel identifier]] (VCI). X.25 provides reliable node-to-node communication and guaranteed QoS.
* [[Frame Relay]], where the VC is identified by a DLCI. Frame Relay is unreliable, but may provide guaranteed QoS.
* [[Asynchronous Transfer Mode]] (ATM), where the circuit is identified by a [[virtual path identifier]] (VPI) and [[virtual channel identifier]] (VCI) pair. The [[Asynchronous Transfer Mode#Reference model|ATM layer]] provides unreliable virtual circuits, but the ATM protocol provides for reliability through the [[ATM adaptation layer]] (AAL) Service Specific Convergence Sublayer (SSCS) (though it uses the terms ''assured'' and ''non-assured'' rather than ''reliable'' and ''unreliable'').<ref name = "I.363.3">ITU-T, ''B-ISDN ATM Adaptation Layer specification: Type 3/4 AAL'', Recommendation I.363.3 (08/96), International Telecommunication Union, 1996, p5.</ref><ref name = "I.363.5">ITU-T, ''B-ISDN ATM Adaptation Layer specification: Type 5 AAL'', Recommendation I.363.5 (08/96), International Telecommunication Union, 1996, p5.</ref>
* [[General Packet Radio Service]] (GPRS)
* [[Multiprotocol Label Switching]] (MPLS), which can be used for IP over virtual circuits. Each circuit is identified by a label. MPLS is unreliable but provides eight different QoS classes.