> But what if we have a four port switch(A,B,C,D) and A,B and C all try
> to send a packet to D at the same time. Would a collision happen?
It really depends on the switch design. Switches that use a "store and
forward" approach and have per-port buffering will be okay, as the
inbound packets on each interface will be buffered and sent out on D in
the order they arrived at the switch. A switch that has no buffering
capability (likely in the situation you described with a four port
switch) and is using "cut through" forwarding will generate a collision
on at least two of the ports because the destination port is busy.
Remember, a switch is just a multi-port bridge. It isolates the
collision domains hanging off of each port, meaning that if you have
multiple systems attached to a port, traffic and collisions on that
segment will not affect other segments. Cross segment traffic acts
like bridged traffic.
Think about what would have to happen if a packet came in on port A
destined for port D, but there were already two machines hanging off of
D that were talking to each other.
-jan-
--
Jan L. Peterson
Unemployed "Computer Facilitator"
http://www.peterson.ath.cx/~jlp/resume.html
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