Answer

The jam signal in CSMA/CD is sent after a collision is detected so that all stations on the shared Ethernet medium become aware that a collision has occurred.

Why it is needed

A station detecting a collision transmits the jam signal, ensuring the collision is long enough to be noticed by other transmitting stations. The affected stations then stop the current transmission and apply the collision backoff procedure before trying again.

Exam-ready: The jam signal informs other stations of a collision and ensures the collision is propagated throughout the shared medium.