Editing Carrier-sense multiple access (section)

{{short description|System allowing transmitters to take turns on a shared media}}

'''Carrier-sense multiple access''' ('''CSMA''') is a [[medium access control]] (MAC) protocol in which a node verifies the absence of other [[Network traffic|traffic]] before [[Transmission (telecommunications)|transmitting]] on a shared [[transmission medium]], such as an [[Bus (computing)|electrical bus]] or a band of the [[electromagnetic spectrum]].

Under CSMA, a [[transmitter]] uses a carrier-sense mechanism to determine whether another transmission is in progress before initiating a transmission. That is, it tries to detect the presence of a [[carrier signal]] from another node before attempting to transmit. If a carrier is sensed, the node waits for the transmission in progress to end before initiating its own transmission. Using CSMA, multiple nodes may, in turn, send and receive on the same medium. Transmissions by one node are generally received by all other nodes connected to the medium.

Variations on basic CSMA include addition of [[Collision (telecommunications)|collision]]-avoidance ([[CSMA/CA]]), collision-detection ([[CSMA/CD]]) and collision-resolution techniques.