IEEE Standard 802.3 (CSMA/CD)

The IEEE 802.3 standard is for a CSMA/CD (carrier sense multiple access with collision detection) LAN. While a station wants to transmit, it links to the cable.  If the cable is busy, the station waits till it goes idle; or else it transmits immediately. If two or more stations simultaneously start transmitting on an idle cable, they shall collide. All colliding stations afterwards terminate their transmission, wait a random time, and repeat the entire process all over again.