Editing Virtual circuit (section)

==Virtual call capability==
In [[telecommunications]], a '''virtual call capability''', sometimes called a '''virtual call facility''', is a [[service feature]] in which:

*a [[telephone call|call]] set-up procedure and a call disengagement procedure determine the period of communication between two [[data terminal equipment|DTEs]] in which [[User (telecommunications)|user]] data are transferred by a [[packet switched]] network
*end-to-end [[Call transfer|transfer]] control of packets within the network is required
*data may be delivered to the network by the [[call originator]] before the call [[access phase]] is completed, but the data are not delivered to the [[call receiver]] if the [[call attempt]] is unsuccessful
*the network delivers all the user data to the call receiver in the same [[sequence]] in which the data are received by the network
*multi-access DTEs may have several virtual calls in progress at the same [[time]].

An alternative approach to virtual calls is [[connectionless communication]] using [[datagram]]s.<ref name="tanenbaum">{{Cite book |last1=Tanenbaum |first1=Andrew S. |title=Computer Networks |last2=Wetherall |first2=David J. |publisher=Pearson |year=2011 |isbn=978-0-13-255317-9 |edition=5th international |page=361}}</ref>

In the early 1970s, ''virtual call'' ''capability'' was developed by British Telecom for [[Packet switching#EPSS|EPSS]] (building on the work of [[Donald Davies]] at the [[National Physical Laboratory (United Kingdom)|National Physical Laboratory]]). The concept was enhanced by [[Rémi Després]] as ''virtual circuits'' for the [[Packet switching#RCP|RCP]] experimental network of the French [[Postes, Télégraphes et Téléphones|PTT]].<ref>{{Cite web |last1=Smith |first1=Ed |last2=Miller |first2=Chris |last3=Norton |first3=Jim |date=2017 |title=Packet Switching: The first steps on the road to the information society |url=https://www.npl.co.uk/getattachment/about-us/History/Famous-faces/Donald-Davies/UK-role-in-Packet-Switching-(1).pdf.aspx?lang=en-GB |access-date= |website=National Physical Laboratory}}</ref><ref name="RCP">{{cite web |title=RCP, The Experimental Packet-Switched Data Transmission Service of The French PTT |date=21 January 2022 |url=http://www.rogerdmoore.ca/PS/RCPDEP/RD.html}}</ref><ref>R. Despres, "A packet switching network with graceful saturated operation", in Computer Communications: Impacts and Implications, S. Winkler, Ed. Washington, D.C., 1972</ref>