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.

1 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.)

  • 1
    Thanks for you answer, but just to make sure: Other NIC then the one sending the JAM signal can have a lower random wait time then the one that sends the JAM signal. correct?
    – Flikk
    Jan 5, 2016 at 9:27
  • 2
    Yes. Random means RANDOM.
    – Ricky
    Jan 5, 2016 at 10:05
  • Binary Exponential Backoff Protocol ( en.wikipedia.org/wiki/Exponential_backoff )
    – Lord Loh.
    Apr 6, 2017 at 5:06

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