Carrier Sense Multiple Access With Collision Detection - Jam Signal

The jam signal is a signal that carries a 32-bit binary pattern sent by a data station to inform the other stations that they must not transmit.

The maximum jam-time is calculated as follows: The maximum allowed diameter of an Ethernet installation is limited to 232 bits. This makes a round-trip-time of 464 bits. As the slot time in Ethernet is 512 bits, the difference between slot time and round-trip-time is 48 bits (6 bytes), which is the maximum "jam-time".

This in turn means: A station noting a collision has occurred is sending a 4 to 6 byte long pattern composed of 16 1-0 bit combinations. Note: The size of this jam signal is clearly beyond the minimum allowed frame-size of 64 bytes.

The purpose of this is to ensure that any other node which may currently be receiving a frame will receive the jam signal in place of the correct 32-bit MAC CRC, this causes the other receivers to discard the frame due to a CRC error.

Read more about this topic:  Carrier Sense Multiple Access With Collision Detection

Famous quotes containing the words jam and/or signal:

    Terror is as much a part of the concept of truth as runniness is of the concept of jam. We wouldn’t like jam if it didn’t, by its very nature, ooze. We wouldn’t like truth if it wasn’t sticky, if, from time to time, it didn’t ooze blood.
    Jean Baudrillard (b. 1929)

    Perhaps having built a barricade when you’re sixteen provides you with a sort of safety rail. If you’ve once taken part in building one, even inadvertently, doesn’t its usually latent image reappear like a warning signal whenever you’re tempted to join the police, or support any manifestation of Law and Order?
    Jean Genet (1910–1986)