10Base5/Thicknet (was Re: SUN networking problems) - test-drb@ccmp.vtda.org

24 Mar 2001

From: jpero(a)sympatico.ca &lt;jpero(a)sympatico.ca&gt;
...
    I haven't
been following this thread as close as I should.
 I was working at Intel during the period when ether net was just
 being defined. The reason for the 2.5m spacing was to insure that
 any collision was detected by all of the unit on the wire.
 The idea was that the pulses would be exactly overlapped. This was 
 In that case, surely the correct spacing of transceivers would depend on
...
  the velocity factor of the cable. And while the
stnadard specifies the
 spacing (2.5m +/- 5cm IIRC), it doesn't specify the velocity factor
 (other than it must be greater than 0.77 IIRC). 
I recall that in musical stuff and in wirings often these waves
travelling in any tube or wirings tend to be standing waves that why
that marking is where the amptitudes is greatest.

Standing waves in this case would be a reflection of poor termination
and cause errors.

The measure was to inustre that using the resolution of the system
you could resolve to half the distance of a tap (1.25 meters or
less than 5ns).

The velocity factor of the specified cable doesnt vary much
or at least not much if it's in spec.  FYI yellow pipe is very good
cable.  I could use 100ft of it right now.

Allison