[Cisco] Local vs Remote vs Late Collisions -- calling all experts

[Kevork Krozian]

  Hi Folks,

        I am wondering if anyone can help me here. 
I am reading contradictory information about Collision types on Ethernet.

 Local collisions look OK.  These happen during the first 64 bytes of transmission ( also known as slot time ). There is an amplitude increase on the local segment, and both Rx and Tx wires become active hence the collision. The sending machine has to resend. No problems here.

 Remote Collsions . Happen on the other side of repeaters, which is does not send back the amplitude increase or send back a signal on the Rx wire. However, these must happen while the sending machine is still transmitting the first 64 bytes which means it is still transmitting when a remote collision occurs. See Slide 6.2.6 Semester 1. 
 The question is :  Is the sending machine still transmitting for a remote collision to occur? If not, then is it not a Late collision ? Also, how can the sending machine know there was a remote collision ? Does it get fragments of the collision back across the repeater with the FCS not matching ? and does that happen before the 64 bytes slot time is exhausted ?

  Late Collisions :  These happen after the slot time is exhausted and the sending machine does not know there was a collision. The higher layers handle the error.

   I am happy to hear any and all suggestions


With thanks

   

Kevork Krozian
IT Manager , Forest Hill College
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