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In [[computer networking]], '''Carrier Sense Multiple Access With Collision Avoidance''' (CSMA/-CA) isbelongs to a [[Mediaclass Accessof Control|mediumprotocols accesscalled control]]as (MAC) [[communications protocol|protocol]] in which:CSMA-CA.
CSMA CA stands for: '''Carrier Sense Multiple Access With Collision Avoidance'''.
In CSMA-CA, a station wishing to transmit has to first listen to the channel for a predetermined amount of time so as to check for any activity on the channel. If the channel is sensed "idle" then the station is permitted to transmit. If the channel is sensed as "busy" the station has to defer its transmission. This is the essence of the "collision avoidance" part of the protocol.
*a [[Carrier wave|carrier]] sensing scheme is used,
*a [[data]] station that intends to transmit sends a [[jam signal]]
*after waiting a sufficient [[time]] for all stations to receive the jam signal, the data station transmits a [[frame (telecommunications)|frame]]
*while transmitting, if the data station detects a jam signal from another station, it stops transmitting for a random time and then tries again.
==Detail==
CSMA/CA is a modification of pure [[Carrier Sense Multiple Access]] ('''CSMA'''). Collision avoidance is used to improve the performance of '''CSMA''' by attempting to reservebe "less greedy" on the networkchannel. If the channel is sensed busy before transmission then the transmision is deferred for a single"random" transmitterinterval. This isreduces the functionprobability of thecollisions "jammingon signal"the in '''CSMA/CA'''channel.
CSMA-CA is used where [[CSMA-CD]] cannot be implemented due to the nature of the channel. CSMA-CA is used in [[802.11]] based wireless LANS. In a wireless LAN, not all stations can "see" all other stations. Hence, collision detection is no longer an option.
The performance improvement is achieved by reducing the probability of collision and retry. Extra overhead is added due to the jamming signal wait time, so other techniques give better performance. Collision avoidance is particularly useful in media such as radio, where reliable collision detection is not possible.
==Usage==
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