CSMA/CD who sends after collision?

Question

I was told that after a collision, the first device that detects the collision and sends the JAM signal has somehow priority to send first after the collision.

I do not believe that this is true and tried reading the IEEE 802.3 section 1 to find the details.

But all I understand so far, is that after sending the JAM signal, the device tries again after a random time.

My theory is that after the JAM signal ends, every device that is in the collision domain waits for a random time after which each device tries to send again. So there would not be any priority.

I hope that any of you can clarify for me, if it is random who sends first after a collision or if any of the devices in the collision domain has any priority after a collision.

Answer 1

Your read of the spec is correct. After the random backoff period, the NIC is free to transmit again. The key to this working is everyone picks a different amount of time. Naturally, someone will pick a smaller number and be free to transmit first -- collision, thus, resolved. If a collision happens again, everyone pauses for a longer random period. After several successive collisions, an excessive collision error is raised and the packet is dropped.

(This is all academic as nobody does half-duplex anymore. No one has made true hubs for decades.)