In computer networking, CSMA-CA belongs to a class of protocols called as 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.
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 be "less greedy" on the channel. If the channel is sensed busy before transmission then the transmission is deferred for a "random" interval. This reduces the probability of collisions on the 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.
Usage
- GNET an early proprietary LAN protocol
- 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 WLANs (802.11 mainly relies on physical carrier sensing though).
- IEEE 802.15 (Wireless PAN) uses CSMA/CA
See also
Carrier sense multiple access with collision detection (CSMA/CD), (used for Ethernet) takes a different approach to the same problem.
Source: derived in part from Federal Standard 1037C