On Mar 24, 20:24, ajp166 wrote:
> From: jpero_at_sympatico.ca <jpero_at_sympatico.ca>
> > > 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.
That can't be the case with 10Mb thick ether because the distance between
markings is about 1/9th of the wavelength.
I did find one thing that relates back to something Bill mentioned in an
earlier post about specific lengths.
>From http://www.ots.utexas.edu/ethernet/10quickref/ch3qr_4.html
The specifications note that the thick coaxial segment should
ideally be built using a single piece of cable from the same
cable spool or from cable spools all manufactured at the same
time (known as a cable lot). If cable from different lots is
used to build up a thick coax segment, then the specifications
note that the sections of cable used should be 23.4 meters,
70.2 meters, or 117 meters in length (all lengths may be +/-
0.5 meters). The reason for using these lengths of cable is to
minimize the chance of having excessive signal reflections
build up due to the slight variations in electrical
characteristics that can occur between different cable
manufacturers or cable lots.
The basic distance quoted is the same as the distance I calculated
yesterday for one bit time: 23.4m.
--
Pete Peter Turnbull
Network Manager
Dept. of Computer Science
University of York
Received on Sun Mar 25 2001 - 05:20:31 BST