Carrier-sense multiple access with collision avoidance: Difference between revisions

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''' Carrier-sense multiple access with collision avoidance''' ('''CSMA/CA''') in [[computer network]]ing, is a network [[multiple access method]] in which [[Carrier signal|carrier]] sensing is used, but [[Node (networking)|node]]s attempt to avoid collisions by transmitting only when the channel is sensed to be "idle".<ref name="federalstandard">{{cite web|url=http://www.its.bldrdoc.gov/fs-1037/fs-1037c.htm |title=Federal Standard 1037C |publisher=Its.bldrdoc.gov |date= |accessdate=2012-09-09}}</ref><ref name="atis">{{cite web |url=http://www.atis.org/tg2k/ |title=American National Standard T1.523-2001, Telecom Glossary 2000 |publisher=Atis.org |date= |accessdate=2012-09-09 |deadurl=yes |archiveurl=https://web.archive.org/web/20080302071329/http://www.atis.org/tg2k/ |archivedate=2008-03-02 |df= }}</ref> When they do transmit, nodes transmit their packet data in its entirety.love u

It is particularly important for wireless networks, where the collision detection of the alternative [[Carrier-sense multiple access with collision detection|CSMA/CD]] is unreliable due to the [[hidden node problem]].<ref>{{cite web|url=http://www.eunice-forum.org/eunice99/027.pdf |title=Study of different CSMA/CA IEEE 802.11-based implementations, Universitat Politècnica de Catalunya |format=PDF |date= |accessdate=2012-09-09}}</ref><ref name="eunice">{{cite web|url=http://arxiv.org/ftp/arxiv/papers/1003/1003.4070.pdf |title=Comparative study of hidden node problem and solution using different techniques and protocols, Journal of Computing |format=PDF |date=2010 |accessdate=2016-01-05|author1=Viral V. Kapadia |author2=Sudarshan N. Patel |author3=Rutvij H. Jhaveri }}</ref>

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Collision avoidance is used to improve the performance of the [[Carrier sense multiple access|CSMA]] method by attempting to divide the channel somewhat equally among all transmitting nodes within the collision ___domain.

# '''Carrier Sense''': prior to transmitting, a node first listens to the shared medium (such as listening for wireless signals in a wireless network) to determine whether another node is transmitting or not. Note that the [[hidden node problem]] means another node may be transmitting which goes undetected at this stage.love u

# '''Collision Avoidance''': if another node was heard, we wait for a period of time (usually random) for the node to stop transmitting before listening again for a free communications channel.

::* '''Request to Send/Clear to Send''' (RTS/CTS) may optionally be used at this point to mediate access to the shared medium. This goes some way to alleviating the problem of hidden nodes because, for instance, in a wireless network, the Access Point only issues a ''Clear to Send'' to one node at a time. However, wireless [[802.11]] implementations do not typically implement RTS/CTS for all transmissions; they may turn it off completely, or at least not use it for small packets (the overhead of RTS, CTS and transmission is too great for small data transfers).