Why did this repair work? 5

[wahnula]

Hello wire-heads,

I am looking for some enlightenment. I had a problem that was repaired, but when I posted this solution in another forum I was questioned as to why it worked, and since I didn't do the repair, I have no clue. The backstory:

I ran a 100' length of CAT6 between a gigabit switch and the LAN NIC of my server, and had about 10-15' of cable left over, so I coiled it neatly in a 12" loop and laid it on the floor by the switch. I started having dropped connectivity issues between the switch and the SBS2003 server. It also showed up as an error in my server eventlog that the connection was lost and then regained several times a week. The workstations all confirmed this with the requisite Windows pop-up balloon.

When I asked my MCSE tech, who was in-office on another issue, about the lost connectivity, he simply picked up the loop, gave it a half-twist, and placed a zip-tie in the middle, leaving a "figure-eight" looking coil. The problem has been gone ever since. He muttered something about "canceling it out" as he is reluctant to share "trade secrets" with me that could put him out of a job, I guess.

I would like to know if anyone is familiar with this repair and could explain it to me. It seemed so intuitive to the tech that I thought it must be a common problem, but nobody in forum602 had heard of it and some were doubting that it could have worked...but it did...so here I am seeking the science behind the repair.

Can anyone shed some light on this? Thanks.

Tony

Users helping Users...

 

[dagwoodsystems]

All I know is that the General Requirements section of TIA/EIA-568-B.1 only recognizes solid core cable for use in horizontal wiring (up to 90m), and stranded for the last 10m for "work room" patch or jumper cables.

I have not been able to find any documentation suggesting that one type of conductor is more or less impervious to EMI/RFI than another. As Skip pointed out, the key difference is that stranded offers physical flexability at the expense of attenuation (formerly known as insertion loss).

I DO know that as impedence mismatch between pairs increases, so does the cable's ability to reject outside interference. It may just be that it's more difficult to manufacture a well-balanced cable out of stranded core than it is to build one with solid. Stranded cables typically have 56 conductors (7 individual conductors wrapped about each other), while solid has...drumroll...just 8 conductors.

Tim Alberstein

http://www.dagwoodsystems.com

 

[dagwoodsystems]

My typo: As impedence mismatch between pairs increases, so does a cable's INABILITY to reject outside interference.

I sure wish this forum would introduce an edit function.

Tim Alberstein

http://www.dagwoodsystems.com

 

[wires]

Geez...

Back when I was a kid and old "electrician" told me that running a load off a coil of romex would cause a fire. Being the curious type I tried it. With 250' of 12AWG at 20 amps there was no fire, not even any detectable heat.

Later I heard the stories about coils of twisted pair cables and induction effects and being the curious sort I tested that. I could never find a problem in testing or operation. For testing I made a rig of 50', 100' and 300' coils of cat5 wrapped in a large bundle. I could never detect any appreciable differences from a straight cable, even with a 100Mhz scope and signal generator running at power levels considerably above 100BaseT levels.

IMHO most of these "stories" about inductance effects are bunk. I have yet to see one in real life while operating within the parameters of common applications for the cables used. Repeatability of the problem is the key. If you can make the same thing happen predictably then the fix could be based on an actual effect. Anything else reeks of black magic and incantations.

These sort of stories are very good at getting everybody worked up and offering off point issues like "crimping solid wire is not professional my opinion" and "specs specify 22 feet of patch cable in a run".

I am glad wahnula network works properly even though I have my doubts about the veracity of the story and the "bowtie" effect.

 

[dagwoodsystems]

Excellent! There's nothing like this kind of experimental data when it comes to uncovering the truth. And your results seem to square with everyone's experience and opinon so far.

Assuming that the MCSE didn't tell wahnula a "story" (or simply forget to mention a key detail), what really fixed this problem? Do you have any theories?

Tim Alberstein

http://www.dagwoodsystems.com

 

[lopes1211]

I have seen lots of cable issues disappear at night in my troubleshooting (i.e. when no other PC's are running traffic in the same wire bundles). issues 9-5, no issues weekends and holidays (could never figure out how the electrons knew it was a holiday). I would think WIRES "antenna/no antenna" experiment would only be valid if tested in a high EMI area/location like a data center or an area with known interferance. Not trying to argue, just saying the environmental specifics of WAHNULA's example involve more than just a bundle of wire laying on a test bench.

-CL

 

[oldtimerbob]

Gigabit has less tollerance for many of the factors that determine how it will perform, including the distance and the type of patch cord used in conjunction with the rest of the system, that is why we use cat6 (perferably cat6A) for this application.

Inserting the figure 8 at the 'service loop' was and is a good idea to get rid of any induction A(EMI), but using a tie wrap is not advised, try using a piece of velcro instead,not tight but snug.
You are always held by the 100 meter rule for the entire run, including the distance of the workstation patch cord and the data panel to switch cord. The shorter the better.
Using factory made cords is best as they should have documentation that they have been tested and meet the spefications for the application.
Even the cable dressing of the runs, to make them look neater where they can be seen (such as where they enter the area of the panels)is in question due to the new limits set to reduce cross talk, etc,etc.

Good Luck,

Has been in the cabling business for about twenty years and is now the Sr PM for a cabling company located in the Los Angeles area.

http://www.globusinc.net

Also a General Class Amatuer Radio Operator.

 

[wahnula]

Wow...lots of spirited debate...and loads of info for open minds like mine. I did not try and troll for reactions, just asking a question.

Alas, the exact scenario can never be repeated, as now all the gear that was VERY close to the loop (within 12") is now elevated another 24" but I can try to replicate it anyway, as the loop will have to be re-done along with all the other wiring.

The EMI scenario makes the most sense...you need to see this trailer...mid-70's, half the trailer on the same AC circuit, fluorescent lights in the entire trailer flicker when I turn on my engineering copier (which is on a dedicated circuit). It's garbage in-garbage out with our AC situation, even the new dedicated outlets.

In the corner of the office where the gear sits is a window A/C unit, phone lines, cable drop, along with the UPS, all the wall warts, cable modem, router and switch. It was all neatly laid out until the new carpet went in.

Thanks for all the information, trust me not one word of it was wasted on me, I enjoy hearing all sides of the issue from professionals.


Tony

Users helping Users...

 

[schoebo]

mmmmmmmmmmm seems like the data liked the 8 more then the 0 lol why ask why drink bud dry.