Extending the demarc for a PRI 3

[feeple]

The MPOE running into our building is in a closet 200 ft of cable from our own utility closet. The telco installed a 50 pair extension between the main phone closet and our own utility closet to bridge this 200ft. The two NIUs we use are located in the main phone closet and use 4 of the 50 pairs to make it to our part of the building. I couldn't get the telco to extend the demarc for our data T1 into our unit, so I did it myself.

The telco did extend the demarc for our PRI into our utility closet. Another 15 feet from that jack is our PBX. As a temporary measure for testing, I contructed a straight through cable (1,2,4,5) to run the length along the floor such that I could coordinate a turn-up with AT&T. Worked fine, no issues. People call in and out using it daily.

Since then, I've tried a couple of different times to run a similar cable up through the ceiling to neaten things up a bit. Doing so adds about 10 more feet to the total length. The trouble is, the PBX and NIU no longer sync when I plug everything in using the new cable. I've tried it with two new lengths of cable (Cat5e), both with the same result. What's really strange is the cable in the ceiling is running right next to our data T1 that I personally extended. The data T1 works perfectly.

I called the phone company and asked what they thought of the situation thinking they could make an adjustment or two from their side and they acted like I was the first person in history to ever have had such a problem.

Because I can't get a good signal with anything other than my hodge-podge cable running along the floor, I have to keep going back to it.

What else can I try?


Site:

http://www.feeple.com

Location: SF Bay Area

 

[ArmstrongTelecom]

Sounds like a cable problem. The 10 foot shouldn't matter.

Ideally throw a tester on it and wire map the working circuit and copy it to the new cable.

If you make both cable connections identical to the original it should work.

You could also re-run the cable and make sure you aren't running too close to EMI or RF sources.

Daniel Armstrong

http://www.armstrongtelecom.com

http://www.vodavi-online.com

 

[feeple]

Tester showed the cable ends were crimped properly in both cases. If EMF and/or RF was the problem, I'm not sure why the data T1 that runs along the same path doesn't have the same issue.


Site:

http://www.feeple.com

Location: SF Bay Area

 

[jml2665]

real basic, using your cable tester and a hard loopback plug, see if you got continuity, and if so reverse transmit and and receive and see if that helps

 

[feeple]

I've done a continuity test, no problems there.

When you say reverse transmit and receive, you mean the polarity, correct? Been there, too.

My tester is pretty basic, polarity and continuity are it's most elaborate features. Can you suggest a more robust unit that might tell me some more about what's going on without breaking the bank?

Site:

http://www.feeple.com

Location: SF Bay Area

 

[Dexman]

One quick way to all but eliminate the possibility of a marginal cable would be to purchase one that is pre-made and see if that works any better.

 

[ISDNman]

<< called the phone company and asked what they thought of the situation thinking they could make an adjustment or two from their side and they acted like I was the first person in history to ever have had such a problem.>>

You realize this is probably their response to any problem of any kind!

After hours I would try swapping the known good cable from your data T1 over to the the voice PRI.

If the problem stays with the PRI at least you can stop chasing your tail.

If it does stay with the PRI, then the LBO (line build out) switch settings on the CSU. If this is an active smart jack it should have a LBO setting as well. If you can access the smart jacks take a look at the card/unit for each of the two circuits and see if there are DIP switches that are nto set identically.

What is the brand/model of the smart jack?

Good luck

 

[mikeydidit]

I normally run a cat 3 shielded 2 pair cable for extending our T-1's. This cut down on the possibilities of EMI across your circuits. This may solve your problem.

"Wise men speak because they have something to say; Fools because they have to say something."
(Plato)

 

[hawks]

You are using the same box of cable that was used for the Data and the working PRI patch cable? The reason I say that is because I've also went back to clean up a run for a T1 and found that the Box of cable I was using turned out to be bad. It passed with the Cable Tester (cheap unit) but I could never get the T1 to come up. After finally using cable from another box (don't remember what made me do it) the span came right up.

 

[ISDNman]

I too have seen weird stuff with Cat 5e and T1's. My best guess has always been that the unterminated pairs were picking up noise. Cat 3 is all that is needed, and sheilding is a good idea. Not sure why Cat 5e does not always work, but I have seen cases where certain house cables did not work for no apparent reason.

 

[jml2665]

reverse the transmit and receive pairs is what I meant, if you have your transmit pair connected to their transmit pair the thing won't work.

 

[SYQUEST]

This subject has been covered in previous posts. But the fact is CAT 5e is for ETHERNET not T1/DS1. DS1 has different characteristics and requirements.
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Here is an article from Quabbin Wire about this (minus figures):

The use of T-1 and T-3 Telco circuits to interconnect LANs is growing rapidly. This article explains how these cost-effective circuits work and why they are so popular.


T-1 and T-3 Circuits Provide LAN to WAN Interconnection

Internetwork Growth Continues

Local area networks (LANs) are getting larger, faster and more complex. Campus, metropolitan, and wide area networks are more common. Network administrators want one local network to communicate with others across campus, across town or in another city. Branch office systems periodically transfer data to or from headquarters locations.

Local and long distance telephone carriers have historically been the first choice for internetwork transmission. They use existing multiplex transmission technology, commonly referred to as T-1 and T-3. These are digital time-division-multiplexing (TDM) schemes, developed many years ago by AT&T to increase the voice channel capacity of circuits between their central offices. After the breakup of AT&T, these technologies became ANSI industry standards, now designated DS-1 and DS-3 respectively.


How TDM Systems Work

Simply put, TDM equipment processes multiple voice or data channels by first converting them from analog to digital, then giving each a unique--but very brief--timing sequence. The TDM electronics allow each channel to transmit its message or data during its allotted time slot. At the other end of the circuit, a demultiplexer breaks apart the rapid, multiple-channel, digital data stream and reassembles it again into discrete voice or data channels.

TDM technologies essentially multiply the capacity of copper cable. Instead of one cable for each channel, multiple channels can be run through a single cable. The following chart summarizes the capacity of each.


Designation Number of Channels (DS0) Capacity (Mbps)
T-1 or DS-1 24 1.54
T-3 or DS-3 672 44.74


The beauty of these Telco transmission technologies is that they are digital, they are available and they are effective for high speed data transmission. T-1 provides 24 channels of 64 Kbps bandwidth (DS0), totalling 1.544 Mbps. (The slightly larger bandwidth is due to timing and framing requirements.)


Fractional and Multiple T-1

Fractional portions of a T-1 circuit are also available from the local telephone carrier in increments of a single channel. Thus, a network can lease 4 or 5 channels if needed; however, the economics currently work out to be break-even for 8-10 channels, as compared to the cost of a full T-1 line equal to 24 channels. T-1 and fractional T-1 circuits are currently most prevalent for multi-LAN interconnection, supporting voice, video, data and FAX.

Although T-1 circuits are most common, T-3 circuits are becoming less rare. T-3 or DS-3 provides the equivalent of 28 T-1 circuits, or 44.7 Mbps of bandwidth. T-3 circuits can be used to provide ultra high speed switched multimegabit data service (SMDS) and even asynchronous transfer mode (ATM) network interconnection. Flicker-free video, exotic image processing, desk-top teleconferencing and other cutting edge computer technologies require this super bandwidth.


T-1 Connection Methods and Devices

Many cabling types and methods may be used to connect networks to DS-1 circuits. The most common is copper cabling, but fiber optic, coaxial, microwave and even satellite transmission links may be used. The best solution for a given installation depends on point-to-point distances, the local telephone carrier's equipment, bandwidth requirements and budget constraints. Of all interconnect options, copper and fiber are the most commonly used.

Fiber offers advantages over copper with regard to EMI immunity, maximum distances and potential bandwidth. However, copper is often already in place, and the total connection cost is less because the DS-1 devices that are required for copper are simpler and less expensive than fiber devices. Thus, copper cabling is often the most practical choice.

When T-1 service enters a building, it is routed through various types of patching and interface equipment. Customer service units (CSU) or digital service units (DSU) process both voice and data channels. These devices convert the digital T-1 transmission signal to a LAN-acceptable digital data signal or voice channel, and the reverse for outgoing traffic. The diagram below illustrates how T-1 or DS-1 Telco service interfaces between different LAN and voice premises.



Copper cable used to transmit T-1 and T-3 signals has been available for many years. A typical design is 2 pair 22AWG with foam skin insulation, each pair shielded, with 100 ohm impedance. These are commonly known as ABAM telephone cables. The physical size of these cables requires termination with DB-15 connectors, punch-down hardware or mechanical terminal blocks. These older cable designs and their termination systems were developed for T-1 applications when they were confined within a telephone company's central office facility.

Now that T-1 and T-3 circuits are finding their way into LAN wiring closets, the requirements have changed. Most new DS-1 system interface devices utilize either shielded or unshielded 8-position Telco modular connectors. The older ABAM cables are too large to fit these relatively inexpensive and widely used connectors.


*****Cabling Confusion*****

The local Telco service supplier usually provides T-1 service into the entrance facility or to the "Demarc" point, and then the LAN owner or installer must take it from there. Since many LAN installers and owners are unfamiliar with the requirements for T-1 cabling, many use the wrong
cabling. For short runs (less than 30 or 40 feet), just about any 100 ohm shielded cable will work, but longer runs often cause equipment to fail. Installers have tried using Category 5 UTP, 50 ohm security cable, cash register cables, or anything that will fit into a modular connector. Most do not realize that the cabling must support specific DS-1 system requirements that are defined by an ANSI specification. These include bit error rates, EMI shielding, a pulse shape definition and many others. The scope trace below illustrates an actual DS-1 data pulse and the limiting minimum and maximum pulse-mask shape. In short, DS-1 systems are far different from LAN Category 5.


Quabbin Wire's New T-1 Cable

Quabbin Wire has developed several cable designs that meet both the electrical requirements for DS-1 data and also terminate to an 8-position modular connector system. These patent pending cables employ a unique two-layer dielectric system, which provides a very stable 100 ohm characteristic impedance, low capacitance, low loss and a high velocity of propagation. By removing the outer insulation layer, the inner will fit into either a shielded or unshielded 8-position modular connector system for an efficient crimp termination. The cables provide T-1 interconnection for cutting edge LAN systems and can be terminated using all customary methods, including the cost and labor saving 8-position modular connector system.

For a detailed review of the performance characteristics and dimensions of these cables, check out P/N 9720 and P/N 9745 in the Cable Finder. Both cables are identical electrically, however P/N 9745 has a zip cord jacket design, which permits the transmit and receive leg to be separated yet contained within its own jacket. This feature is important for some installations when these circuits are physically separated by some distance on the equipment. You can review these constructions as well as other part numbers by selecting T-1 (DS-1) from the Cable Finder's Application Menu <../finder/finder.cgi?cmd=app_form>. Also review the Independent T-1 Test Verification <tech1.html> for this cable, found on the Technology Briefs </techbr.html> page, and look for the many new additions to our T-1 family.

Copyright © 2000 Quabbin Wire & Cable Co., Inc. All rights reserved.
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For the missing figures, go to the website: quabbin.com for this and other info.

Hope this clarifies the subject!

....JIM....

 

[feeple]

Thanks Jim.

So, mikeydidit's method of using shielded Cat3 looks to be my best bet. I'll give it a shot.

--Kurt

Site:

http://www.feeple.com

Location: SF Bay Area

 

[SYQUEST]

Hi Kurt,

I see you are in the North! I'm in the "OC". I have had lots of interesting experiences over the years with T1. I worked for a paging company and we did lots of T1 stuff. Using the right cable can make the biggest difference. It's like using the right RG coax in radio and RF. The wrong stuff might work OK in one or two instances, but sooner or later you will get one that just beats your two-pair!

I had the least problems by using cable like the Quabbin or when that is not available for example, Telco runs a 100-pair house cable to extend the DEMARC but still puts the NIU shelf at the .1 terminal. What you do is put all the XMT sides in one binder group and the RCV sides in another binder group. This is what telco has done for years when "T screen" cable wasn't available. The performance turned out to be pretty good. But two of the important things are keeping the transmits and receives separate by having them shielded and the 100 ohm impedance characteristic to maintain the T1 waveform envelope. Otherwise all kinds of squirrelly can occur similar to your experiences.

Good luck!

....JIM....

 

[jconrad0305]

When ever i extend a t-1 and i have done hundreds i run a cat5e cable terminated with female jacks on bothsides and then use factory made cat5e patchcords to connect to equipment. i have never had a problem.

 

[feeple]

Figured it out.

The mistake I made was in trusting the telco's wiring. The problem was between the NIU and the customer convenience block (demarc). I re-punched down their wires and tightened the screws up a bit it the block and all is well.

My part of the wiring was fine all along. Using Cat5e and it's fine.

Thanks for all the help/suggestions!

Site:

http://www.feeple.com

Location: SF Bay Area

 

[ISDNman]

Glad you got it going.

I have seen it works with one side open on short runs!

Thanks for letting us know what you found.

 

[aarenot]

do not tell the telco you did that, or they might get a bit mad.

You do not always get what you pay for, but you never get what you do not pay for.

 

[feeple]

The telco suggested I do it, finally got someone cool on the phone. They didn't have to ask twice.

If I had done it without their go-ahead, I'm sure it would have been the very first time anyone ignored the PUC rules and monkeyed with stuff on the telco's side of the demarc.


Site:

http://www.feeple.com

Location: SF Bay Area

 

[aarenot]

notice i said, do not tell them, and not, do not do that, lol. not that i have ever done anyhting like that, no, no, never, never, uh uh uh. lol



You do not always get what you pay for, but you never get what you do not pay for.