🚀 go-pugleaf

In article <Bz0vA3.D9G@news.iastate.edu>, john@iastate.edu (John Hascall)
wrote:
> 
> [*please* stick to < 80 columns...]
> 
> jim@mivax.mc.duke.edu (James D Dryfoos - Systems) writes:
> }I am trying to find out if there is a point during transmission
> }of an ethernet packet that the
> }transmitting card stops listening to the wire to see if...
> 
> Yes, the ethernet chip(set) will notice the collision.  A collision
> after 512 bits is a `late collision'.  A late collision indicates your

A late collision should not occur because any Ethernet card
is supposed to *listen* before it starts talking.  In their
advertisements during the early days of Ethernet, XeroX used
to compare this to *polite* people at a cocktail party: you
don't interrupt somebody else; you wait for a pause.  Thus a
collision should only take place when two cards attempt to
begin transmitting at about the same time.  The so-called
"collision window" is the time period during which a collision
can occur on a properly-functioning network because collision
detection cannot be instantaneous.  This is the main reason
for having a minimum packet size, a maximum segment length, and
the 4-repeater restriction: to ensure a sufficient collision
window for detection to work.

A late collision means that some device is transmitting when
it should *not* be doing so.  Properly-functioning devices can
detect and report a late collision as an error, but they cannot
solve the problem because the device which is the cause has
already demonstrated its inability to follow the rules.

(of course, in the cocktail party analogy at this point the
boor who interrupted would get shouted down...)

Matt Healy
"I pretend to be a network administrator;
 the lab net pretends to work"

matt@wardsgi.med.yale.edu