Editing Virtual circuit (section)

{{Short description|Emulation a dedicated physical link over a packet-switched network}}
{{technical|date=August 2012}}

A '''virtual circuit''' ('''VC''') is a means of transporting data over a data network, based on [[packet switching]] and in which a connection is first established across the network between two endpoints. The network, rather than having a fixed data rate reservation per connection as in [[circuit switching]], takes advantage of the [[statistical multiplexing]] on its transmission links, an intrinsic feature of packet switching. 

A 1978 standardization of virtual circuits by the [[CCITT]] imposes per-connection [[Flow control (data)|flow controls]] at all user-to-network and network-to-network interfaces. This permits participation in [[congestion control]] and reduces the likelihood of [[packet loss]] in a heavily loaded network.<ref>{{cite web| publisher=ITU-T| url=https://www.itu.int/rec/dologin_pub.asp?lang=e&id=T-REC-X.25-199610-I!!PDF-E&type=items| date=October 1976| title=X.25 - Interface between Data Terminal Equipment (DTE) and Data Circuit-terminating Equipment (DCE) for terminals operating in the packet mode and connected to public data networks by dedicated circuit}}</ref><ref>{{cite book| chapter-url=https://www.academia.edu/77340340| author1=Rybczynski, A| author2=Wessler, B| author3=Després, R| author4=Wedlake, J| title=Proceedings of the June 7-10, 1976, national computer conference and exposition on - AFIPS '76| chapter=A new communication protocol for accessing data networks: The international packet-mode interface| editor=AFIPS| date=1976-06-07| page=477| doi=10.1145/1499799.1499869| s2cid=8790311}}</ref> Some circuit protocols provide [[Reliability (computer networking)|reliable communication service]] through the use of data retransmissions invoked by [[error detection]] and [[automatic repeat request]] (ARQ). 

Before a virtual circuit may be used, it must be established between [[network node]]s in the [[call setup]] phase. Once established, a [[bit stream]] or [[byte stream]] may be exchanged between the nodes, providing abstraction from low-level division into [[protocol data units]], and enabling higher-level protocols to operate transparently.

An alternative to virtual-circuit networks are [[datagram]] networks.