When a station transmitting in CSMA/CD detects a collision, it doesn't just stop silently — it immediately sends a short jam signal (typically 32–48 bits) onto the channel.

Purpose of the jam signal:

1. To ensure that all other stations on the shared medium become aware that a collision has occurred, even those that may not have detected the collision themselves (e.g. due to their position on the cable).
2. This guarantees the collision lasts long enough to be reliably detected by every transmitting station involved, so none of them mistakenly believe their frame was sent successfully.
3. It prompts all colliding stations to stop transmitting and enter the random backoff (exponential backoff) phase before attempting retransmission, avoiding repeated immediate re-collision.