Editing Packet switching (section)

==Packet switching in networks==
In telecommunication networks, packet switching is used to optimize the usage of [[channel capacity]] and increase [[Robustness (computer science)|robustness]].<ref name=":20" /> Compared to [[circuit switching]], packet switching is highly dynamic, allocating channel capacity based on usage instead of explicit reservations. This can reduce wasted capacity caused by underutilized reservations at the cost of removing bandwidth guarantees. In practice, [[TCP congestion control|congestion control]] is generally used in IP networks to dynamically negotiate capacity between connections. Packet switching may also increase the robustness of networks in the face of failures. If a node fails, connections do not need to be interrupted, as packets may be routed around the failure.

Packet switching is used in the [[Internet]] and most [[local area network]]s. The Internet is implemented by the [[Internet Protocol Suite]] using a variety of [[link layer]] technologies. For example, Ethernet and Frame Relay are common. Newer [[mobile phone]] technologies (e.g., [[GSM]], [[LTE (telecommunication)|LTE]]) also use packet switching. Packet switching is associated with connectionless networking because, in these systems, no connection agreement needs to be established between communicating parties prior to exchanging data.

[[X.25]], the international [[CCITT]] standard of 1976, is a notable use of packet switching in that it provides to users a service of [[flow control (data)|flow-controlled]] [[virtual circuit]]s. These virtual circuits reliably carry variable-length packets with data order preservation. [[DATAPAC]] in Canada was the first public network to support X.25, followed by [[Transpac (data network)|TRANSPAC]] in France.<ref name="Transpac paper"/>

[[Asynchronous Transfer Mode]] (ATM) is another virtual circuit technology. It differs from X.25 in that it uses small fixed-length packets ([[cell relay|cells]]), and that the network imposes no [[flow control (data)|flow control]] to users.

Technologies such as MPLS and the [[Resource Reservation Protocol]] (RSVP) create virtual circuits on top of datagram networks. MPLS and its predecessors, as well as ATM, have been called "fast packet" technologies. MPLS, indeed, has been called "ATM without cells".<ref>{{cite web|url=http://www.certificationzone.com/cisco/newsletter/SL/interview_08-12-03.html|title=Interview with the author (of an MPLS-based VPN article)|archive-url=https://web.archive.org/web/20070929150800/http://www.certificationzone.com/cisco/newsletter/SL/interview_08-12-03.html|archive-date=2007-09-29|first=G.|last=Pildush}}</ref> Virtual circuits are especially useful in building robust failover mechanisms and allocating bandwidth for delay-sensitive applications.