A Collision Domain is defined as all the Ethernet* segments between a pair of bridges or other layer 2 devices. The reason for this is that all traffic must appear on all the cables between bridges. Thus if a frame is transmitted from a station on a concentrator, all the stations on that concentrator will see the frame at nearly the same time.
A collision occurs when a station begins transmission and then receives the beginning of a frame from another station. The station will immediately stop transmission and issue a JAM signal onto the wire. This will indicate to the other transmitting station that a collision has occurred and both stations will back off for a random amount of time and try to re-transmit.
This back-off time is dependent on the number of consecutive collisions that were issued before a successful transmission. The more collisions, the longer the maximum back-off time.
This mechanism requires that stations be close enough together for each station to see any possible attempted transmission before the first 64 bytes of its frame have been transmitted. This is because 64 bytes is the minimum frame size for an Ethernet network.
This applies to: