On Sat, 01 Oct 2011 22:05:39 -0400, wrote:

On Sat, 01 Oct 2011 20:32:11 -0500, "
wrote:

On Sat, 01 Oct 2011 21:14:12 -0400, wrote:

On Sat, 01 Oct 2011 19:26:46 -0500, "
wrote:

On Sat, 01 Oct 2011 19:59:33 -0400, wrote:

On Sat, 01 Oct 2011 17:21:18 -0500, "
wrote:

When I was in the cabling biz at IBM I set un an experiment with CAT-3
trying to break an Ethermet or a Token Ring LAN doing every urban
legend bad thing anyone could think of (loops of cable over
fluorescent ballasts, running next to 480v 1600a feeders, taped to the
raceway, telephone in the same cable, exceeding the 300' rule, etc)
Basically I couldn't break it.

10-baseT, 4/16MB T/R only?

The original installation was 16mb TR but we also tried 10/100
Ethernet and it ran clean at 100 mb doing big file transfers and
looking at the logs. For the "over length" test I hooked the kludge we
had up to a new 300' spool so we had that plus the other hundred foot
baseband cable we were playing with and whatever was in the rack,
cables etc.

I'm somewhat surprised 100BaseT worked over CAT-3.

So was everyone but then there were a lot of people who said you would
never see copper running at a gigabyte. Now it is old technology.
bit?

yes sorry

That's sorta cheating, though. It's no one wire/pair.

it is still 500 a pair.

1000BaseT uses four pairs, so it's 250Mb per. Three bits are encoded per
pair, per symbol, so the symbol rate is 62.5MHz (MBaud).

The whole thing got started when someone said we were having problems
because the router (in a rack) was backed up to the equipment room
wall where they had that 1600a service.

The router was bad.

Hate it when that happens.

I hooked up the spool, just for playing with TDR to get a little more
time down the wire but I had to try it. ;-)

TDRs are great tools. Too bad they're so rare (I suppose the people who know
how to use one are even more rare).

We were doing TDR on a Tektronics 485.

What were you using as the pulse generator? I used HP 140s (w/TDR plugins) in
college and 7904s (7S10/7S11s) in IBM. There have been many times I wished I
had one around.

You just use that 18" cable nobody seems to know why the have and
couple the trigger out on the side to the" in" with a BNC "T" and
bounce that signal down the line. You sync on the fall of the trigger
pulse and look for the echo. It really works pretty well but you need
a fast scope since you are looking at nanoseconds. You ain't doing it
with a 453 unless you have some real long wire.

Ah, it seems they're using the trigger out as the pulse generator. Neat, but
I'm surprised it's fast enough. That rise time is critical. Even the antique
HP TDR pulsers were something like 25pS.

I think a guy in Raleigh figured that out. It was part of the 7800
remote support training.
I really only did it once to fix something but I did find the
offending drywall screw in a coax on a 100' run in 3 tries.
(found the screw heads that were close with a magnet and backed them
out with a screwdriver)
Third one was the charm. Once I took the screw out it worked so well
they left the coax in the wall.

Slick. ;-)