sundance-communications.com Forums Telephone Services T1's, CSU's and DSU's T1 extend IW - how to test

Hi All,

Apologies if this should be in the cabling forum..

I have a failing p2p-T1 (CRC errors) which AT&T tell me is certainly my IW. They had an engineer at each end, disconnected the buildings, clean for 30min in the middle, put the building on and noise is seen from the IW side.

There are 5 SmartJacks at the MPOE which take the following route:
SmartJack-RJ45 -- CAT6 UTP 10' to 66-block
66-block over 25-pair telephone up to 3rd floor 66-block
cross connect (1') to another 66-block on the 3rd floor
3xCAT6 from the 3rd floor 66-block to the wiring closet 66-block.
(there are 2xT1 sets in each CAT6, so RX(1)+TX(1), RX(2)+TX(2) in one cable, RX(3)+TX(3),RX(4)+TX(4) in the 2nd, RX(5)+TX(5) in the last)

I don't know the run length of either the 25-pair or CAT6 from the 3rd floor to the closet.

At the wiring closet it terminates at a 66-block, breaks out to 5 x RJ45 jacks, then each jack has a CAT6 patch (10') to the T1 WIC's in Cisco 1841's.

It worked fine when originally installed but since who know how many cable pulls and punchdowns on those blocks has become noisy.

It strikes me there may be several problems:

1) Running RX+TX for multiple T1's seems bad, general opinion says all RX's in one cable, all TX's in another. Also read T1 cable should be shielded pair within shielded cable, but don't know if that applies for "extending"
2) Possibly too far. The Cisco indicates 655' but I don't know about the SmartJack
3) Cable type? Mixing CAT6 and whatever twisted pair is considers.
4) Number of junctions/wire break.

I am trying to have a hole drilled through the wall as the SmartJacks are only about 50' from the WIC. Then it would be (1) a dedicated conduit (2) single cable from each SmartJack to each Cisco WIC.

The other thing I cannot seem to get an answer to is: How can I certify or simply check the wire end-to-end within the building? I only have a Cat6 certifier, do I need a T1 certifier?

This is beyond my knowledge. All the other T1's I manage are where the WIC is within 10' of the SmartJack, so it's just a straight through cable.

Any help is much appreciated.

When extending T1 circuits, I would avoid using UTP and go with cable that is designed specifically for that purpose. Untwisting pairs to punch down on the 66 blocks negates any advantages of selecting CAT6 cable.

Are you sure that you have RJ45s? I'm thinking that if you do, that could be your problem. You'd only have a transmit pair. These connections should be via RJ48 wiring patterns.

Next, the telco's 'smart card' has to be configured with the appropriate line build out (LBO) settings. The default is 133 feet maximum, which is where the installers typically leave them. You'll need to inform them of any distances that reach farther so that they can set the card accordingly.

The CAT6 wiring is a complete waste of time and money. With the 25 pair cable in the equation, CAT6 gains you absolutely nothing: The proverbial weakest link. These circuits work ideally on individually shielded transmit/receive pairs, but in the real world, they are fairly tolerant to many site conditions.

I wouldn't waste my time by 'improving' the cable run with CAT6 segments. Have the telco simply configure the CPE side of their interface facility to permit a longer run and tolerance. You'll be fine after that.

RJ45: My bad, I meant RJ48 (too much ether!)
CAT6: Only thing the installer had on hand I believe.

So does this seem a reasonable course of action:
1. Figure out the total run length and get the TelCo to reconfigure accordingly if over 133'.

If I'm still seeing problems (or run is less than 133'):
2. Forget the existing wiring and replace the 4 segments with the correct shielded cable.

and finally if I'm still seeing errors

3. Either:
Bore the hole in the wall to get a clean, short run of cables.
--OR--
Single run from SmartJack to WIC of shielded cable (200-400' at a guess) for each T1.

Again, thanks for the help.

A conduit would be my preferred choice, with separate shielded cables for T and R sides on all circuits.

If that's a no-go, then a bunch of shielded cables all the way through, with no mid-point punchdowns.

With the second option you still might have to get AT&T to adjust the LBO.

My $0.02 only...

Good luck.

Two pair, 22AWG overall shielded cable with each pair separately shielded will work miracles in this situation. This cable is not cheap or easy to find, but it is the best solution.

The second-best solution will be to run two separate cables, one containing the transmit and one containing the receive.

I still think that if you can get the telco to adjust the LBO settings on the CPE side to match your total cable length, you will be able to use the existing infrastructure.

Keep in mind that CAT6 adds a significant amount of conductor length due to the tight pair twists. Count on about double the length of a traditional foot of cable as a general reference.

T1 circuits aren't nearly as delicate as people lead us to believe, but anything that you can do to improve the delivery path will help.

Whenever I extend T-1 circuits, I use a dedicated Cat5 cable with RJ-45 plugs on each end. In some cases we will terminate to mini patch panels, but mostly just modular plugs. One less point of failure that way. I even test the cable so it passes certification standards. Now you have a completely clean extended cable that the LEC or CLEC can't question.

I'm with Ed. At the very least use two different cables for transmit and receive. CAT5 or 6 is not needed. The two pair shielded is the best, especially for long runs. Getting rid of all those failure points (connections) is probably what will fix it.

If you must use your 25 pair use a low count for one side and a high count for the other to keep the trans and rec apart.

On March 21 we kicked around a problem similar to this under T1,Csu,DSU TITTLED "T1 Extension"

Hi.

I have seen twin shielded cable (figure 8)used for T1 extensions. Not very often, but I have seen it. Usually it contains two or three pairs in each part. I guess this implies you can run two or three T1 circuits through this cable. Is this right?

Also, shouldn't the wire shields be connected to something at one or both ends? Are pins 3,6,7 and 8 possibly grounded in the smart jack? Should the shielding be connected to them? I have also heard of grounding plugs that are conductive. plastic. Or sometimes you see plugs tht have metal sides. Should one of those be used?

I don't see how you can meaningfully certify a cable for T1 using a Cat6 tester. The nature of the signals is very different. As discussed many times on this board, phone lines are "cat 0" and there is no performance advantage of using cat 3, 4, 5 or 6 cable for phone lines.