Re: Ethernet connection sensitive to cable length

Re: Ethernet connection sensitive to cable length
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Subject Author Date
Re: Ethernet connection sensitive to cable length ps56k 05-03-2008
Posted by ps56k on May 3, 2008, 12:37 pm
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added cabling & ethernet newsgroups -
Wonder if a small ethernet cable tester has been used to verify proper pairs
?
--

windsurferLA wrote:
> Ethernet linked access point appears sensitive to cable length well
> below specified limits.
>
> I’m seeking to locate a wireless access point remote from my main
> router, a D-Link DI-524 whose wireless function has been turned off.
> The wireless access point is being implemented with a nearly identical
> D-Link DI-524 wireless router whose DHCP function has been turned off.
> The IP address of the second D-Link DI-524 wireless router has been
> altered so as not to conflict with the IP address of the first router.
> One of the LAN outputs of the first router is connected to one of the
> LAN outputs of the second router so that it acts like a switch.
>
> I have tested the above configuration at three locations linked by
> three different CAT5 cables.
>
> Location #1 – WORKS fine when linked by commercially constructed 10’
> long CAT5 cable.
>
> Location #2 – WORKS fine when linked by home built 40’ long CAT5
> cable.
> Location #3 – DOES NOT WORK when linked by home built 100’ long CAT5
> cable. – Not only is there no communication over the link, but the
> lights on both routers do not even indicate a connection. YET, if at
> this same location #3, the 100’ long cable is plugged into any one of
> several computers, the connection indicator lights come on
> immediately, and full normal network access is quickly obtained.
>
> As the cable length is well under the 100 meter (300 feet) maximum
> length for Ethernet, at first I thought that maybe the third cable is
> somehow wired differently, perhaps as a “Cross over cable” rather than
> as a “straight through” cable. I understand that some interfaces can
> cross and un-cross a cable automatically as needed. I am uncertain
> whether or not the LAN ports of the DI-524 have that feature, but an
> examination of all of my cables, both home made and commercially
> assembled, and all appear to be wired “straight through.”
>
> I’ve also sought to confirm that the problem is not associated with
> the RJ45 connector at the end of the cable. The symptoms are
> unchanged when a short (10 foot long) Ethernet extender (female to
> male) cable is used, so the connector at the end of the 100’ cable is
> not disturbed as I switch between the D-Link DI-524 and my lap-top
> computer..
> Any Suggestions?



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Posted by Robert Redelmeier on May 3, 2008, 4:22 pm
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> windsurferLA wrote:
>> Location #2 ? WORKS fine when linked by home built 40? long
>> CAT5 cable. Location #3 ? DOES NOT WORK when linked by home
>> built 100? long CAT5 cable. ? Not only is there no communication
>> over the link, but the lights on both routers do not even
>> indicate a connection. YET, if at this same location #3, the
>> 100? long cable is plugged into any one of several computers,
>> the connection indicator lights come on immediately, and full
>> normal network access is quickly obtained.

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


Posted by Jeff Liebermann on May 3, 2008, 9:34 pm
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On Sat, 03 May 2008 20:22:07 GMT, Robert Redelmeier

>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.

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.

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

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.

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

Perhaps a matchmaker would be appropriate?

>-- Robert

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

Posted by Robert Redelmeier on May 3, 2008, 11:04 pm
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> On Sat, 03 May 2008 20:22:07 GMT, Robert Redelmeier
>>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.
>
> 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.

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.

> 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.

Easier to notice and fix with jacks.

> 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.

Nice data point.

-- Robert


Posted by Jeff Liebermann on May 4, 2008, 12:29 am
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On Sun, 04 May 2008 03:04:43 GMT, Robert Redelmeier

>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.

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.

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

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

>> 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.
>
>Easier to notice and fix with jacks.

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.

>> 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.
>
>Nice data point.

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

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