atcomsystems.ca/forum Forums Wiring - Telecom Carriers - Trunks & Services T1's, CSU's and DSU's 2 Wire T1 vs. 4 Wire T1

Rob -

10' should be no problem at all. Not to disagree with Ed (Which is ALWAYS a losing proposition) I would keep a single cable at 50' or less and stick to Cat 5 or better for it. That's just based on my experience. Your mileage may vary.

Sam

Here is a quick writeup on HDSL:

https://www.arcelect.com/HDSL3698.htm

I know that this topic was originally started late last year but as a Telecom tech, I would like to advise the readers of my own recent experience with 2 wire vs 4 wire T1 circuits for voice traffic.

One week ago, I had to de & re a phone system for a customer that relocated to another city. At their old location they had 2 T1 circuits that were 4 wire and we never had any problems with them for almost 5 yrs that they were in that location. At their new location, the T1 circuits were 2 wire circuits.

About 3 days before the move, I brought out a test system to the new location for the turn up and test. No, I don't have a T-bird for testing. At first, I kept getting "Out of Frame" errors on my system on both T1s, which the CLEC was able to stabilize after making adjustments somewhere and then the turn up and test went smoothly. On the day of the move, after re-installing the system, sporadically, I would get Yellow Alarms, which sometimes would last anywhere from 10 seconds to about 2 minutes.

Opening a trouble ticket with the CLEC, they looped and tested to both the smart jack and to the system's CSU for about 30 minutes each on both T1s. After the testing and unlooping, again we started getting hits on both T1s. The local Telco, which is AT&T, came out and moved both T1s to new pairs and they then appeared to be working properly. I asked the AT&T tech how far it was from the CO and he said it was less than 4000 ft.

The next business day, which was the customer's first work day, the sh*t hit the fan, both T1s kept going down all day. Again they tested them and they ran clean but the customer still had problems with the circuits. The tester for the CLEC tried to claim it must have been a problem with the customer's equipment but I explained to them that this equipment had been in and working for over 4 years with out any problems. By the way, this customer has had this same type of equipment at other locations without any problems either.

I wasn't involved in any other conversations over this problem but finally, just yesterday, the CLEC sent out a tech with a T-Bird for another vendor meet. He tested the first T1 for 20 minutes with only 2 errors, tested the second T1, which he said was clean. Then he tested the first one again and almost immediately he got over a million errors and at first he wanted to put the blame on the cabling for the extended T1s from the Smart Jacks at the NIUs, which are on the first floor to the customer's suite on the fourth floor. He went downstairs and tested it directly at the NIU and got similar results.

The CLEC opened a new trouble ticket with the local telco, why it was only put in for the first T1, I don't know but last night they reconfigured it as a 4 wire circuit and it has been up all day with out any problems, the second T1 though, which is still a 2 wire circuit, went down 6 times today. They called the CLEC to have AT&T to convert the 2nd T1 to a 4 wire circuit too.

I'm convinced that 2 wire T1s just aren't as stable as 4 wire circuits. At least not T1s for voice channels. Maybe data only circuits have the same problem but it isn't apparent because they only think their network is slow when it's down. Of course with VOIP being used more and more, they will realise the problem if they any VOIP connections over those T1s, like remote extensions, networked systems or use SIP trunks.

Now they are going to have to figure out who is going to be responsible for all my extra time I've spent on this, which will cost them somewhere between $800 and $1000 more than the original estimate for the de & re!

Chuck,
There was something else going on there... From what you've written I can't figure out WHAT is was… But the HDSL2 technology has proven itself VERY reliable for several years and it is actually more resilient than 4-wire due to only needing two conductors.

There really is no difference either on voice or data… 1.544 Mbps is what a T1 one is. What’s IN the train of bits does not matter to the Telco equipment that’s used in HDSL2 it keeps the training a rolling at a fixed (timed) 1.544 Mbps.

Hi all,

I'm new to this forum, just wanted to say what a great place with knowledgeable people.

I'm a relative newbie (3 yrs), started with FIOS splicing and have been doing copper most of my 3 yrs. I work for Verizon in NE Indiana and nowadays we do EVERYTHING from the CO frame to fixing cable to CPE to computer work (DSL contracts). A handful of us install and repair special ckts (T1, analog, etc).

Since we have a large area, some of the old independents Verizon (GTE) acquired used what we call traditional 4w T1s where you had your pr separation with shielded cable and long hauls (most of them are for CO or RSU (huts) to Muxes).

In the city its fiber (lite-span) muxes. The T1s are 4w HDSL 1st gen, HDSL4, or HDSL2. The prs assigned are whats left in the count, or what we can use that's good - without any consideration for what binder generally. HDSL4 is used when HDSL2 reaches the maximum attenuation spec (length, gauge, etc).

HDSL4 is definitely more robust than 2w, but I think the main problem with all of these flaky ckts is:
1) Are the prs REALLY clean? (faults, dirty splices, bridge tap, etc.)
2) Is the ckt falling well within specs (dB, S/N, atten)
3) Is the HTU-C (CO card) any good? Sometimes when ckt goes down when all else has been done and the remote testers say its good to the office the card is erring on the cable pr side of itself.
4) Have the protector modules (5 pin) been changed, and are they the right type rated for hi-cap ckts? If the demarc screw in tube type and they're carbon, they can break down and throw errs.

The ADTRAN cards that have the T-SCAN diagnostic built in can clue you in on what is going on alot of times. We plug our laptop in to the craft interface (RS-232) and look at the Margin (of S/N ratio) fluctuation, Atten (dB), history of err/sec, severely err/sec, Unavailable (down) sec.

The nice thing about working on HDSL4 with repeaters is loopable repeaters to isolate what section pr faults are in. The traditional T1 you gotta goto each can, pull the repeater, next can, next can, put em all back in....Plus with HDSL I can loop myself w my laptop (which should of been done before ticket sent outside).

Sorry for the long story, and believe me I respect you guys and your decades of experience, I just wanted to give you my perspective of how I work ckts.

And THANKS again for all the info, I've sure learned alot in the posts you "Old-timers" have done!

Welcome to the board!

You've given us a lot of good information - Thanks! Stop back regularly, ask for help if you need it, give help if you can and have a good time always.

Sam

HDSL2 (ADC/ADTRAN) is held to the same standards as a repeatered T1 facility by ILEC's. HDSL2 modulates a 4-wire DS1 payload onto a boradband/analog carrier between 2 digital transceiver units(HDSL Line Unit/HDSL Remote Unit)over 1 2-wire cable pair. HDSL2 does not work as well as a repeatered T1 facility on marginal OSP facilities due to it using only a single conductor for its simplex power loop between the HLU & HRU. Light ground-faults and high-resistance opens and shorts that may not typically cause troule or go unnoticed on a T-1 facility can play havoc on HDSL2/4. As long as it is carried over healthy OSP facilities between the telco and customer, HDSL is just as reliable as any other DS1 transport technology.

And on a side note. Don't bother wasting your time plugging a T-BERD or any other T1 test set up to an HDSL span with the intent on it taking errors by sending a certain stress pattern. Those stress patterns were developed to troubleshoot a purley digital facility with its associated loop electronics and wiring(ie* T-1). Sending differnet patterns of 0's and 1's isn't going to make a difference to the analog waveform of the HDSL span. The only reason to connect a BERT device to a DS1 circuit being transported on HDSL 2/4 is to troubleshoot the wiring and electronics on either side of the HDSL span and line-coding and framing options.