Local collision

A local collision, in CSMA/CD computer networks, is a collision that occurs at the NIC as opposed to on the wire.

On UTP cable a local collision is detected on the local segment only when a station detects a signal on the RX pair at the same time it is sending on the TX pair.

Since the two signals are on different pairs there is no characteristic change in the signal. Collisions are only recognized on UTP when the station is operating in half-duplex. The only functional difference between half and full-duplex operation in this regard is whether or not the transmit and receive pairs are permitted to be used simultaneously.

It is important to know that a NIC cannot detect local collisions without attempting to send information.

Faulty cables that cause crosstalk can cause local collisions as the RX and TX chatter on the same PC can fool it.