Editing Packet switching (section)

==Concept==
[[File:Packet Switching.gif|thumb|350px|This animation illustrates a network model in which consecutive packets between hosts take differing routes. Out-of-order delivery is, however, detrimental to the performance of several network protocols, including TCP, so [[Internet|the Internet]] attempts to route packets associated with the same [[data stream]] along the same path most of the time.<ref>{{cite IETF| rfc=2991| title=Multipath Issues in Unicast and Multicast Next-Hop Selection| date=November 2000}}</ref>]]

A simple definition of packet switching is:
{{blockquote|The [[routing]] and transferring of data by means of addressed packets so that a [[Communication channel|channel]] is occupied during the [[transmission (telecommunications)|transmission]] of the packet only, and upon completion of the transmission the channel is made available for the transfer of other [[network traffic|traffic]].<ref>{{cite book|first=Martin|last=Weik|url=https://books.google.com/books?id=ZCYBCAAAQBAJ&q=packet-switching&pg=PA718|title=Fiber Optics Standard Dictionary|publisher=Springer Science & Business Media|date=6 December 2012|isbn=978-1461560234}}</ref><ref>{{cite book|author=National Telecommunication Information Administration|url=https://books.google.com/books?id=xSa_AAAAQBAJ&q=addressed+packets+of+data&pg=SL16-PA1|title=Telecommunications: Glossary of Telecommunications Terms|publisher=[[Government Institutes]]|date=1 April 1997|isbn=1461732328|volume=1037, Part 3 of Federal Standard}}</ref>|sign=|source=}}

Packet switching allows delivery of [[variable bit rate]] data streams, realized as sequences of short messages in fixed format, i.e. ''[[Network packet|packets]]'', over a [[computer network]] which allocates transmission resources as needed using [[statistical multiplexing]] or [[dynamic bandwidth allocation]] techniques. As they traverse [[networking hardware]], such as switches and [[Router (computing)|routers]], packets are received, buffered, queued, and retransmitted ([[store and forward|stored and forwarded]]), resulting in variable latency and [[throughput]] depending on the link capacity and the traffic load on the network. Packets are normally forwarded by intermediate network nodes asynchronously using [[first-in, first-out]] buffering, but may be forwarded according to some scheduling discipline for [[fair queuing]], [[traffic shaping]], or for differentiated or guaranteed [[quality of service]], such as [[weighted fair queuing]] or [[leaky bucket]]. Packet-based communication may be implemented with or without intermediate forwarding nodes (switches and routers). In case of a shared physical medium (such as radio or [[10BASE5]]), the packets may be delivered according to a [[multiple access]] scheme.

Packet switching contrasts with another principal networking paradigm, [[circuit switching]], a method which pre-allocates dedicated network bandwidth specifically for each communication session, each having a constant bit rate and latency between nodes. In cases of billable services, such as [[cellular communication]] services, circuit switching is characterized by a fee per unit of connection time, even when no data is transferred, while packet switching may be characterized by a fee per unit of information transmitted, such as characters, packets, or messages.

A packet switch has four components: input ports, output ports, routing processor, and switching fabric.<ref>{{Cite book|last1=Forouzan|first1=Behrouz A.|url=https://books.google.com/books?id=bwUNZvJbEeQC&q=A+packet+switch+has+four+components:+input+ports,+output+ports,+routing+processor,+and+switching+fabric&pg=PA232|title=Data Communications and Networking|last2=Fegan|first2=Sophia Chung|date=2007|publisher=Huga Media|isbn=978-0-07-296775-3|language=en}}</ref>