24 Mar
2001
24 Mar
'01
10:32 a.m.
On Mar 24, 15:07, Dwight Elvey wrote:
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.
As Tony has already pointed out, that can't be completely true, because it
would depend on the velocity factor of the cable, and the standard does
indeed specify only a minimum of 0.77 for that. Typical values for thick
ether are 0.78-0.8, which gives quite a variation. In addition, it would
require that pulses from two stations be in sync, which is unlikely since
there's no master clock.
This was
also the reason for the maximum length without repeaters. The
packet size was such that any collision was sure to be detected,
regardless of where one was along the cable.
Actually, the minimum packet size is what determines the maximum total
length *including* repeaters. The maximum length *without* a repeater is
determined by the signal losses.
It doesn't make any difference where the end
terminations are
placed but both ends need to be terminated.
That's my understanding, too.
--
Pete Peter Turnbull
Network Manager
Dept. of Computer Science
University of York