Carrier-Sense Multiple Access with Collision Detection

Carrier-Sense Multiple Access with Collision Detection (often given as the acronym, CSMA-CD) is a way of controlling access to a LAN using a bus (i.e. a shared broadcast channel on which all stations can hear any station which is transmitting).

What this means is that a station wanting to transmit waits until it hears silence ('carrier sense'), and then starts transmitting. If it 'hears' another station start to transmit while it is so doing (a 'collision' - hence 'collision detection'), it stops, 'backs off' a random delay, and re-tries. (This is essentially exactly identical to what a group of people chatting at a party will do.)`

A versions of CSMA-CA was first used on the ALOHA network, before being adopted for Experimental Ethernet.