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

Revision as of 09:34, 4 August 2006

Revision as of 02:46, 7 August 2006

Line 1:

'''Bold text'''In [[computer networking]], '''Carrier Sense Multiple Access With Collision Avoidance''' (CSMA/CA) is a [[Media Access Control|medium access control]] (MAC) [[communications protocol|protocol]] in which:

*a [[Carrier wave|carrier]] sensing scheme is used,

Line 6:

*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'''). Please visit this article for a complete description of the basic protocol.

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 reserve the network for a single transmitter. This is the function of the "jamming signal" in '''CSMA/CA'''.

Collision avoidance is used to improve the performance of '''CSMA''' by attempting to reserve the network for a single transmitter. This is the function of the "jamming signal" in '''CSMA/CA'''. 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.

==Useage==

*[[GNET]] an early propritory [[LAN]] protocol

*[[Apple Computer|Apple's]] [[LocalTalk]] implemented '''CSMA/CA''' on an electrical bus using a three-byte jamming signal.

*[[802.11 RTS/CTS]] implements '''virtual carrier sensing''' using short '''Request to Send''' and '''Clear to Send''' messages for [[WLAN]]s ([[802.11]] mainly relies on '''physical carrier sensing''' though).

==See also==

Compare use of the jamming signal in [[Carrier sense multiple access with collision detection]] ('''CSMA/CD'''), which(used usesfor another[[Ethernet]]) takes techniquea different approach to improvethe '''CSMA'''same performanceproblem.

Source: derived in part from [[Federal Standard 1037C]]