Jam Signal

Question

Can someone please explain Jam Signal to me? I understand that a Jam Signal is sent to every node in the Ethernet signaling them to not send a signal as collision has occurred. But what is the logic behind it? And why does it take 2*Propagation Time in the worst case?

Answer 1

when there is a collision then jamming signal is sent by sources to alert all the stations that a collision has occured so stations have to wait for sometime ,after than if channel is free they can transmit the packets based on back off algorithm .In the worst case TT>=2PT because when a station sends the frame and the transmission of other frames from other end starts just before reaching the last bit of first station's frame.