Ethernet LAN Re: Ethernet connection sensitive to cable length

added cabling & ethernet newsgroups -
Wonder if a small ethernet cable tester has been used to verify proper pairs
?
--

windsurferLA wrote:

These homebuilt cables, which wiring pattern did you use?
T-568A or -B ?  If you don't know what I'm talking about,
it is highly likely you split a pair.

Please do not complain "but the other comp works".
Difference NICs and drivers are more error-tolerant
and have more robust fall-backs.

Electrons may be color blind, but they _do_ know
who their dance [twist] partners are.

-- Robert

On Sat, 03 May 2008 20:22:07 GMT, Robert Redelmeier


Huh?  Unless he did something really disgusting, like EIA-568A on one
end and EIA-568B on the other, either wiring standard will work.  The
color codes are different, but the pairing is identical.

Drivel:  I once had some hired help in wiring a medical office.  I did
568B while my hired help did 568A wiring.  Nothing worked when we were
done.  Never ignore the obvious.


True.  I recently demonstrated that I can run 10baseT-HDX (half
duplex) through 2,000 ft of CAT5e (two rolls in series), without any
data degradation.  If I had a 3rd roll, I would have added it.  The
catch is that it would only work between my Cisco 1900 ethernet
switch, and a desktop with an Intel Pro100 card.  It would function to
other devices (several laptops, assorted junk around the office), but
these showed various errors in the switch SNMP logs.


Perhaps a matchmaker would be appropriate?


See item #6:
<http://www.LearnByDestroying.com/nooze/support.txt>

--
Jeff Liebermann     jeffl@cruzio.com
150 Felker St #D    http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann     AE6KS    831-336-2558

Oh yes, fully agreed.  But I think it relatively unlikely
the OP would have followed either without some awareness.
I'm testing for that awareness.  

The intuitive wiring patterns (SBS and USOC) will split a pair.
All the correct ones are somewhat counter-intuitive.


Easier to notice and fix with jacks.
 

Nice data point.

-- Robert

On Sun, 04 May 2008 03:04:43 GMT, Robert Redelmeier


I enjoy asking the original questions backwards.  In this case, it's
"what would I have to do, to CREATE the problem"?  Creative wiring and
connector terminations are the probable culprits as the terminating
equipment is obviously working.


I'll do the newsgroup(s) a favor and not rant on how Ma Bell, the old
TIA and the EIA created this mess.


At the time (about 1998), if you purchased any manner of pre-wired
ethernet jumpers, you got EIA-568B wiring.  Never mind that EIA-568A
is the real standard.  Well, my accomplice was working on his BICSI
certification, and they were preaching EIA-568A.  Never mind that I
told him that I wanted the color coding to be consistent throughout
the entire building, all of which was EIA-568B.  He decided that BICSI
must be correct and was fully prepared to have me (not him)
re-terminate the entire building (about 400 wall jacks) to insure
compliance.  I paid him his fee and hired a day worker from the local
lumber yard.  He didn't speak much English, but he undid the damage in
amazingly little time, and finished the job in about half the time I
had expected.  The cable certifier found two wiring errors out of
perhaps 60 wall jacks.  I was going to pay him a bonus, but that was
before I noticed some of my tools had evaporated.  Sigh.


Careful here.  That's not an endorsement for installing 2,000ft CAT5e
runs.  I once calculated the maximum cable length at about 1,200ft for
10baseT-HDX before timing becomes an issue.  Why 2,000ft worked is
still a mystery to me.  It shouldn't have unless the timing on the
ethernet devices is more relaxed than required.  Also, note that I was
using 10baseT-HDX (half-duplex).  Full duplex and/or 100baseT will not
work due to collision domain issues and cable near end crosstalk.  You
also have to use an ethernet switch.  Hubs (repeaters) will not work.

I do have several 900ft runs in service (one of which goes under some
railroad tracks).  No problems.  I do have a 500ft run that is giving
me problems.  I haven't had time to troubleshoot (due access issues),
but am guessing that I have some induced interference from rotating
machinery, transformers, ballasts, or something similar.

As for stretching the technology, I done my part:
1.  DSL over barbed wired.  1Mbit/sec SDSL.  Distance is about 3,500ft
of barbed wire, with 100ft of CAT5e at each end.  However, the
multiple splices tend to be noisy so it was replaced with a wireless
link about 2 years ago.
2.  10base2 (cheapernet) over CATV 75 ohm RG-6/u coax.  Distance was
about 1500ft at one location.  The other location was a radio station
that was stuffed full of RG-6/u coax runs.  Terminated with 50 ohms at
both ends (because 10base2 uses DC levels for busy detection).  Only
two transceivers (no taps or T connectors).  With such high losses,
the far end reflections just disappear and never become a problem.
3.  FTTS (fiber through the sewer).  Actually it's drain under the
road that dumps into the river, but it looks much like a sewer.  About
800ft.  I keep waiting for it to fail as some water propelled rock
cuts the outer jacket, but it's been up for 8 years and shows no
change in fiber attenuation.  I've lost two transceivers, but the
fiber is holding it's own.
4.  In the miscellaneous category, I've done ethernet through the
sewers (in order to cross the LATA boundaries), ethernet over 25 pair
telco bundles, ethernet over two 117VAC extension cords (I was
desperate), DSL over zip cord, and adapters made primarily from clip
leads.  900MHz data over G-Line.  I won't mention any of my other
wireless atrocities.

One of these days, I'll follow the standards and rules, but not this
week.

--
Jeff Liebermann     jeffl@cruzio.com
150 Felker St #D    http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann     AE6KS    831-336-2558