If a collision is heard, both of the senders will send a jam signal over the Ethernet. This jam signal indicates to all other devices on the Ethernet segment that there has been a collision, and they should not send data onto the wire.
For example if u want to wish birthday someone and you know that at 12 o'clock his /her phone get busy then you send jam signal from 11-58 by calling him/her by this way you send jam signal on her/his network and no collision can occur