I'm currently studying about the CSMA protocol and I struggle to understand the meaning of "listen" in the well known definition:
CSMA is based on the principle "sense before transmit" or "listen before talk".
For example: Consider stations A,B. Let's say the cable is idle. So, A starts to transmit (it is true to say that only when finished transmitting, the propagation begins?)
Now, B want to transmit some frame. How B knows that A is transmitting? There is something that A sends to the other station before it start transmitting?