CSMA/CD

A contention method (carrier sense, multiple access, collision detect) in which a transmitting node first tests the channel and, if the channel is clear, then transmits the desired message. If two stations transmit at the same time, the collision is detected and retransmission is forced. Also Carrier Sense Multiple Access with Collision Detection. Media access mechanism wherein devices determine if another device is already transmitting before starting their own transmissions. If no transmission is sensed for a secific period of time, a device can transmit. If multiple devices transmit at once, a collision occurs and is detected by all colliding device. This collision subsequently delays retransmission from those devices for some random length of time. CSMA/CD is used by Ethernet and IEEE 802.3.