In an Ethernet network, a collision is the result of two devices on the same Ethernet
network attempting to transmit data at exactly the same time. The network detects the
"collision" of the two transmitted packets and discards them both. Collisions are a
natural occurrence on Ethernets. Ethernet uses Carrier Sense Multiple Access/ Collision
Detect (CSMA/CD) as its method of allowing devices to "take turns" using the signal
carrier line. When a device wants to transmit, it checks the signal level of the line to
determine whether someone else is already using it. If it is already in use, the device
waits and retries, perhaps in a few seconds. If it isn't in use, the device transmits.
However, two devices can transmit at the same time in which case a collision occurs and
both devices detect it. Each device then waits a random amount of time and retries until
successful in getting the transmission sent.
This was first published in June 2001
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