In computer networking, Carrier Sense Multiple Access With Collision Avoidance (CSMA/CA) is a network control protocol in which (a) a carrier sensing scheme is used, (b) a data station that intends to transmit sends a jam signal, (c) after waiting a sufficient time for all stations to receive the jam signal, the data station transmits a frame,
and (d) while transmitting, if the data station detects a jam signal
from another station, it stops transmitting for a random time and then
tries again.
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.
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.
and (d) while transmitting, if the data station detects a jam signal
from another station, it stops transmitting for a random time and then
tries again.
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.
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.
- AppleTalk implemented CSMA/CA on an electrical bus using a three-byte jamming signal.
- 802.11 RTS/CTS implements CSMA/CA using short Request to Send and Clear to Send messages.
