Proper way to install shielded ethernet

Hi BJ,

Wow, that's a long post. I'm going to have to post on top this time so you can see it ;-)

Anyways, grounding of ScTP cables is a big issue that DOES NOT have a resolution yet. This is because the solution would exist on the intersection of at least two building construction disciplines - electrical power and information transport systems (OK - the last one is just old structured cabling - I've been reading too much BISCI stuff lately ;-)) As such, there will always be two approaches from different angles - safety on one hand and performance on the other. And don't forget the cost of implementation, too. It has always been exorbitant for ScTP considering labor and such.

Bottom line is: in order for the shield to be effective it needs to be grounded on both ends. It creates a need for the point of ground at the work area outlet. Unless you are willing to extend your telecom grounding to EACH outlet, you are stuck using the equipment's power ground that actually belongs to the whole different grounding system and is only connected to the telecom at the grounding rod. Or it could even be connected to another grounding rod! That wholly depends on the building and you are always at the mercy of other people.

Anyways, long story and I gotta go right now. So, I thought the best way to address this would be to release in the open one of our paid e-books, Guide to Separation of Network Cabling from EMI Sources. This document is circa 2000 but not too much has changed since. Check in couple days this page of our site:

Hopefully you'll be able to find useful info there that can help you in your situation.

Cheers,

Dmitriy Abaimov, RCDD

"Dmitri wrote:

A few nuggets of information. Just nuggets, not hearty, satisfying pieces, since it's late and I was gonna sleep before I logged on... :-)

What propted the STP? Some speculation about the future, the present, and the past.

THE FUTURE I consulted with several cabling guys whose opinion I value quite a bit, which led in turn to my own online research. I found just enough information about 10 gig to become convinced that it makes sense to take 10 gig specs into consideration when evaluating the scope and breadth of a recabling job. The speculation comes into play because the standard isn't actually ratified yet, so it'll be jiggling for a while yet before it firms up. BUT, some cabling companies already sell cable that meets some version of the draft standard, and it's nearly always STP. Ampnetconnect has a number of interesting white papers on the subject, but they agree that STP clearly outperforms UTP in 10 gig testing. They may come up with good ways to deal with the ANEXT in the electronics, but for now, it's looking like STP has the advantage. If we can spend an extra 30-40% on the cabling job now, and that gives us another whole generation of network speeds in 10 years (or whenever it comes up), then we'll be very happy we spend the extra amount upfront.

THE PRESENT We've had some very odd application errors that have defied normal troubleshooting techniques. It's not the OS on the workstations, it's not the software environment on the workstations, it's not a gazillion other things that we've ruled out. The network is the one thing we haven't been able to provide with a conclusive alibi. Over the past 11 years, any number of people have poked around in our cieling for any number of reasons, and who knows if they all observed structured cabling standards in their poking? So my current cabling infrastructure is a great big question mark.

THE PAST Work that was done as recently as 2.5 years ago (just before I got there) is suspect. Jacks were terminated with only 2 pair, for example. I don't know anything about the work that was done in prior years, or, again, if structured cabling standards were followed (and 2.5 years ago, they certainly should have been punching down all 4 pair, imho). So again, my current cabling is a big question mark. Since I don't know if there ARE some freakish sources of EMI that are inducing network errors (chances are, not...but when all other possibilities have been ruled out, whatever remains, however unlikely, must be considered), and since STP seems a reasonable prediction for 10 gig applications, it seemed best to make no assumptions and play it extremely safe. You have no idea how irksome these bizzare application behaviours have been.

Also, anecdotally, I spoke to another local admin who recently rebuilt his network from the ground up with new cabling and switches, in preparation for a new VoIP phone system. Wouldn't you know it, the wierd behaviour some of his apps had been exhibiting, and which also defied resolution, suddenly disappeared. His switches had not been reporting errors, yet once everything was swapped out, his apps were suddenly rock-solid. Since his switches hadn't cried foul, he's assumed his network was clean and didn't give it another thought, so he was very suprised (and pleased) to find the issues resolved.

All this speculation led to a fuzzy-logic consensus that going STP on the rewire was worth a shot in the short run, and could likely pay off in the long run.

BJ

(oops...it's past my bedtime.)

Yeah, I have been there too. And I suspect many others have too, but are ashamed to admit it ;-) From every logical engineering perspective that kind of thing should not happen; if your network tests clean it should run clean. But when dozens of servers and high-performance clients starting throwing bits around it doesn't always seem to happen that way.

If you have a typical (central data room) + (remote distribution panels) setup, have you considered using fiber optic for the backbone runs to the remote panels? That can take away a lot of grounding concerns.

Of course, I have also been in industrial situations where we had temperature swings from 35 deg.F (Sunday morning) to 140 deg.F (Sunday evening) (or higher at the top of the building where the cables run). That led to problems that I believe were caused by expansion and contraction of various components touching on the fiber (installed before my time), which led me to call in an industrial cabling guy. I thought to use innerduct and the usual fiber zipcord; he suggested armoured outdoor fiber. Good idea, except "armoured" means a metallic sheath. Which led to an argument over the grounding scheme....

sPh

PS Nice work on getting the discussion over purchasing standards going in your organization! Sounds as if the powers-that-be in your org are open to reasonable arguments if approached correctly.

(snip)

Personally, I am not sure that I believe in alien crosstalk, but assuming that I do, and that it is electrostatic (capacitive) coupling then I believe the shield works as you say.

The problem with discussing shielded cable is that there are many things the shield is expected to do, some of which it can and some it can't.

There are many (non network related) systems that use coaxial cable. In that case, the shield obviously has to be connected at both ends, though possibly to a transformer and not grounded.

The physics is completely different for low frequencies (wavelength longer than the cable) than for high frequencies.

(snip)

If you are trying to keep out low frequency magnetic fields, the physics is completely different. Note that ethernet is pretty insensitive to low frequency magnetic fields, but many audio systems are not. The shielding rules are different for audio.

(snip)

As far as I know, there isn't so much research on alien crosstalk. My belief is that in most cases the cables will be mixed up enough in the cable tray/raceway/etc. that it isn't a problem. If someone is very careful to keep the cables parallel for a long enough distance, maybe, but why go to all that work?

The system should have enough fuses/CB's to protect it.

For low frequency magnetic coupling.

To avoid ground loops, when only one end supplies power.

If the signal is unbalanced, and near a resonance of the shield.

I believe so, for high frequency capacitive coupling.

There is another effect which some believe, which is coupling to unused pairs in a UTP cable. Some believe in it, others don't.

If you take two cables and wire tie them together every foot, I might believe that you can get a measurable alien crosstalk signal. (Be sure to terminate both ends as appropriate.)

If you install 100 cables in a tray, it seems unlikely to me that they will run next to each other for a long distance.

Well, until there is a 10G over copper standard, there is no answer.

The only descriptions of alien crosstalk I have seen are from the cable companies, and we know what they want to sell.

If it really is important, I would expect the 10G ethernet people to work out the solution. Maybe even discuss it here.

-- glen

I believe in crosstalk. Whether it comes from aliens (legal, illegal, or extraterrestrial) is open to debate. ;^)

The *physics* is identical for low and high-frequency effects. The

*simplifying assumptions* and that can be made in practical applications, and the *dominant parameters* (e.g., magnetic vs. electric fields) are different.

-- Rich Seifert Networks and Communications Consulting 21885 Bear Creek Way (408) 395-5700 Los Gatos, CA 95033 (408) 228-0803 FAX

Send replies to: usenet at richseifert dot com

preparation for

suddenly

this has been a great thread, as I've not seen STP since the old Token Ring days.

With the concept of EMI and various types of "noise" on the line, I was wondering is there any kind of "instrument" that could show exactly what the line was encountering over a period of time ? Especially if the switch is not showing ANY type of errors like CRC, etc. ie - what could the line momentarily experience that would not show up as an error ? hmmm - the circuit overloaded so it looks like a continuous collision ?

I was hoping to get you into this discussion... Any thoughts on alien crosstalk in real wiring situations? The ones I read about it in were written by wiring companies.

Also, I haven't been following 10G over copper at all, which seems to be what the OP wants to do.

Well, I still tend to separate capacitive (electric) vs. inductive (magnetic), but yes, each exists independent of frequency and cable length. One important part of physics is knowing which approximations to use, and when. For transmission line physics, inductance and capacitance are separate. I still remember a physics lab experiment with coaxial cables, including one with a high inductance (coiled) center conductor. For transmission line physics, you compute the velocity from the capacitance and inductance per unit length. If you figure out the uncoiled length of the coiled conductor, you get a similar result for the velocity.

Any other comments on what I wrote about shielding of UTP cables?

thanks,

-- glen

Here are some measurements of alien crosstalk in round and flat cables. It seems to indicate that round cables pass, but flat ones fail.

Here is an IEEE report on screened Cat5e cable, (which they call FTP for some reason), and which may be what the OP is using. I believe that screened cable has a thin foil covering, instead of the thick braid that would normally be used for a shielded cable. This also indicates that the shield (screen) can be left floating. It seems that they use screened patch cables, also with the screen left floating, but unless the patch cables are also bundled, I would not expect much alien crosstalk.

(snip)

The effect that I was most considering before is the same one used for SWR meters, where a signal from the inner conductor of a coaxial cable (which is actually a coaxial box) induces a signal going in the same direction in a nearby wire inside the same box. For the SWR meter, this allows separate measurement of the signal going in each direction on a cable. For a transmitter, it is desired that all of the signal go out, and none come back, but that doesn't always happen.

For a balanced UTP cable, this would require pairs with the same pitch within nearby cables to be close and parallel for a fairly long distance. It also assumes pretty good tolerance on the pitch, such that the phase stays the same over the whole length. This would be an electromagnetic effect, combining both capacitive and inductive coupling.

Near end alien crosstalk would seem to be to be only from capacitive coupling, as the effect described above should induce a signal going in the same direction.

-- glen

I had no idea people are still fiddling with flat high-performance cables. You'd think they don't expect it to perform under carpet for too long after being stepped on ...

(F)oiled (T)wisted (P)air - the cheapest and making least sense type of shielded cable. Absolutely impossible to install the shield properly. Most installers just cut the shield an inch short of the jack and connect the drain wire in hopes that this represents a proper installation. In some FTP cable designs I've seen the drain wire is even isolated from the aluminum foil shield with a layer of plastic film. Go figure what they thought it'll be draining...

Yes. Here is my thought: it's a mess right now. The cabling companies should spend couple more years researching on the subject (and not from the marketing stand point) before wrestling each other into accepting the TIA/EIA-568-B.2 Addendum 10. Additionally, testing requirements should be standardized at the same time as CAT6A specs because right now there is no good way to measure alien crosstalk. I walked away from the last presentation by Fluke on the subject with understanding that you actually need at least three CAT6A jacks at each workarea in order to perform a rather simplified (no picking on Fluke - it's a grandiose task!) alien crosstalk testing/certification. How in the real world it is going to fly?

Best Regards, Dmitri Abaimov, RCDD

Cabling Guide, Cabling Forum, color codes, pinouts and other useful resources for premises cabling users and pros

I don't want to judge ethics of what the OP did with the first quote. It happened to me so many times that I was not even surprised to see it openly admitted to on the Usenet. However, it also happened the other way around: a customer sends you someone's bill of materials and wants you to bid on it. What would you do? Say "no, mister customer. It is not ethical and I'm not going to bid and also will report you to BBB for letting me implement someone's design"? Don't judge and you won't be judged. (which does not really help to discourage this frustrating practice, I know)

If you want to sell it, don't call it an estimate. Call it a, say, "system design" which it is, and the estimate is just a part of it. With all the spreadsheets and other estimating aids available I bet you spend more time designing the system than estimating it. Why call it an estimate then?

Yes, that's exactly what you should do. Saying something is "unethical" when you are the injured party is just so much griping unless that behavior is equally unethical when you are the benefitted party.

Don't judge unless you are *willing to be judged*. If you act ethically, being judged is a *good thing* (tm). It can only increase your reputation.

I invariably refuse to work with clients who act improperly, even if it means walking away from large sums of money. I sleep much better at night with a smaller bank balance, but my values intact.

-- Rich Seifert Networks and Communications Consulting 21885 Bear Creek Way (408) 395-5700 Los Gatos, CA 95033 (408) 228-0803 FAX

Send replies to: usenet at richseifert dot com

Oh, that is what flat cables are for? In that case, alien crosstalk shouldn't be a problem.

It seems that according to IEEE, and agreeing with what I said last week, it works even with the shield unconnected as far as alien crosstalk.

If I understand the IEEE one, they also use FTP for patch cables, again not connecting the shield. The other solution is a fatter cable that keeps the pairs farther apart.

-- glen

Fully agreed. Complaints from excess-benefit are much rarer and more credible than complaints from shortage.

Buyer ethics are just as important as seller ethics. Unfortunately, they don't get much attention.

It may not cost you all that much. Buyers who are unethical with someone else are very likely to be the same with you. Rework and scope creep are more likely to occur. And then there's the aggravation.

-- Robert

In my systems administration work for the Canadian federal government, I was involved in purchases from the minor to the moderately large (about a quarter million or so.) Each time, we were very careful about supply ethics, ensuring that all vendors got the same information, that information about competing bids was not passed on, ensuring that as much as practical that there could be competing solutions; and we went out of our way to ensure that vendors really were "sole-source" in the cases where there was only a single reasonable supplier. We were also careful to be consistant and thorough in bid evaluation.

There -were- limits on how much accomedation we were willing to do in order to ensure that multiple suppliers were possible. For example, if one vendor could offer support for all the models of something we had [that we deemed worthy of support contracts], and a second vendor could only offer support for some of the models but not all, then we did -not- split the RFP into two pieces just to be able to offer some work to the second vendor in order to avoid any possible impression that we were deliberately sole-sourcing.

And this is where it gets messy. Electrical service grounds can have voltage on them, especially compared to a ground point being used say at the file server. Especially if you have an electrical fault which is not pulling enough current to trip a breaker. Which can now mean you have current flowing back through the shield to the switch or whatever. And this is never good. For people, equipment, or both.

Which is why all non electrical service grounds (per the current electrical code I think) should be connected all back to the same "earth" ground as the electrical service with no other point of connection. Think about what this would do to your costs if you really want to ground your data cables at each end.

Now think about your phone service. Does it come in at the same place as your electrical service? How about cable TV/data? Do they all follow these rules?

It can get to be a mess real quick especially in older re-habbed buildings.

Fine with me.

It seems that, according to IEEE and for the specific case of alien crosstalk, screened cable with the screen unconnected at both ends does work. Otherwise, for many uses of screening grounding does matter.

Thanks for opening this up. It might be that you attract more people to the paid articles this way! I think I pretty much agree with what it says. The often mentioned one or two foot separation to power lines or fluorescent lighting is overly conservative.

-- glen

Walter Roberson wrote in part:

Good point. I was thinking more of smaller American govt agencies like school boards (Mark Twain's quip holds true after 150 years). This is probably both Cdn-US differences (guardians of the people vs elected by the people) and a function of agency size/competence. I'd expect some US Federal agencies like the GSA to be equally ethical unless they devolve power without control/accountability.

-- Robert