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

Well guys, since this thread is going to become the definitive reference, I want to get a response on two other points.

First, since there are no repeaters, is this distance sensitive?. For example where I live, I have a T at my house because that's all I could get from a distance standpoint. Can this other circuit be ran to a cabin on the top of a mountian many miles from the CO?

Also, speaking of the high voltage issue. I have been told in the past that on a circuit such as this, it could be put in today and work fine. Then as the area around you built up, if you ended up with several of these in the same cable, your service got degradated. Is there any truth to that?

Trace, I can only speak from personal experience. My office is located about 9 miles from our serving CO and there is one underground "hut" along the cable route. Chances are, there is a doubler there. We lost our circuit about a year ago and I was told that it was due to a power supply failure in this hut. This implies that there must be some type of electronic device associated with our circuit in the rack that lost power.

From what I've been told by Verizon technicians, our circuit is on a copper pair the whole way. I know of at least six of these circuits that are working in our office park cul-de-sac, all riding on the same 900 pair distribution cable down our street with no issues whatsoever.

The feed to this general area is comprised of two aerial 2,700 pair 26 gauge cables and one 2,400 pair, 26 gauge cable. There are certainly visible repeater cans and load coils along the route, but they are obviously for unrelated pairs to mine.

I've tried to beat up our circuit a couple of times by shorting or grounding the pair and it always comes right back up. Our distribution cable is 1970's era PIC, so it's not in the best of shape. With that being said, I'd say that it's safe to assume that these circuits are fairly bulletproof. :rolleyes:

Guys -

A lot of good information on this post! This one is a keeper.


Sam

Trace,
HDSL whichever form/generation you use IS distance sensitive. For HDSL2 (2-wire) what sparked your original question, the maximum is 9 Kft for 26 gage; 12 Kft for 24 gage, and 22 Kft on barbwire (19 gage.) Other factors DO play a role in it too. I.E. How much is buried (constant 70 degree F temp) and whether the cable is pic (plastic insulators) or pulp (paper insulation.) So your cabin on the mountain “could” get T1 service on 2-wire if it had good 19 gage cable and was within’ 4 miles or so of a remote. … BUT more than likely I’d be using HDSL4 with up to two repeaters to get to your country home with a view. As long as you was within’ say 7.5 miles from a remote (calculated on 24 gage)

Is there any truth to service being degradated if other similar services were added after yours? …. Uhhhh… My professional opinion is, “kind-a.” LOL. For your HDSL2, no. You really can run a sheath full of those. When applying HSDL 4-wire technology you’re supposed to apply separations to the pair assignments. (Keeping transmit and receive pair out of the SAME 25-pair binder.) If you start running a bunch of Tx’s and Rx’s together in the same 25 count… there’s a CHANCE things will get a little “flakey.”

Ed,
At nine miles (roughly 40,000 feet) there is NO way you’re on copper from the main C.O. There has to be some kind of MUXed T3 carrier or a DLC at the remote (or “hut” as it’s called in your area) where your T1 is placed on copper from.

To achieve THAT kind of distance on copper (which “can” be done) you’d have to still be on old T1 repeater technology… about the only thing that WAS GOOD about those was the ability to use one repeater after another, after another on a copper span. … but if you fatred on those things you’d knock ‘em down and they are NOT auto-realigning.

BTW, you also mention load coils in your post… Load coils are digital signal KILLERS. They HAD to be cut out at the cans before you ever got a digital circuit.

Regarding the degradation of service caused by numerous DSL loops within the same cable: Trace, whomever told you this in the past, was correct. :thumb:

Particularly when more than one pair within a cable's binder group carries high speed data, interference between these data-pairs may increase the error rate for these high speed circuits. Normally, these error rates are maintained at acceptable levels by reducing the transmision level of various services such as ADSL. Unfortuantely, in my experience, this is not possible on HDSL circuits.

When providing HDSL across copper, like Bryan also suggested, try to ensure that the HDSLs are assigned to pairs within separate 25-pair binder groups.

Oh, boy. Its been a while, but out comes the soap box:

I don't know guys..... A binder group is still within the same cable jacket. I don't see how a simple plastic tape strip to bind 25 pairs for identification purposes is going to have any electrical effect on the pairs themselves. Twisted pair cable is designed with varying twist lays so that there's little likelihood of crosstalk or other interference between the pairs. The two circuits could still be right next to each other as the binders are side-by-side within the cable sheath. Everything spirals in a twisted-pair cable of any size, so it's inevitable that the pairs, no matter which ones, are going to come in contact with each other at some point.

Think about this: The cable feeding my building is using pairs 51-75 and my circuit is on pair 51. My neighbor orders a circuit too, sharing the same cable count. The telco isn't going to do an LST so that we are on different binders. His circuit will simply end up on pair 63; the next available pair in the count. I really, really doubt that any thought process goes into assigning circuits to the proper binders.

On the other hand, what if there's not a choice? Plenty of times, a 25 pair cable runs down the road feeding multiple customers. If that theory was accurate, then only one customer could have a Hi-Cap circuit for that entire distribution segment.

What about when a 3,600 pair cable leaves the CO and branches out two miles down the road? In a manhole, this cable splits in two different directions:

To the left is branch cable A, an 1800 pair cable is spliced in as pairs 1-1200 (the remaining 600 pairs in this branch cable are just spare for future use).

To the right is branch cable B, a 1200 pair cable is spliced in as pairs 1201-1500 because only 300 pairs are needed for now. In that cable, the remaining 900 pairs are also left as spares for future use.

Later on, the 1,200 pair count is full in cable A and they need to get 200 more pairs. Bill schleps down into the manhole and cuts the next available pairs through. The first branch cable now becomes 1-1200 and 1501-1700.

How many times have you seen something like this written on a building entrance terminal?

CA 236, 401-600, BP 1-200
CA 117, 201-225, BP 201-225
CA 209, 1801-1900, BP 226-325
CA 9, 2201-2275, BP 326-400

That's right, hook or crook, multiple feeder cables are merged together at some point into the single cable feeding the building. All of these different cable counts end up neatly terminated as binding posts (BP) or pairs 1-400. There is absolutely NO rhyme or reason as to how the binders are assigned with any telco. It's all about throwing the pairs where they are needed and usually a case of borrowing from Peter to pay Paul.

Next time you are driving down the road, look up at the telephone cable splices. You'll frequently see how a cable jumps over to tie two cables together. That's because of the pairs in one cable were running low and the other one had spares, so the original cable got a "refill".

Moral of the story: Binders really don't mean a hill of beans in the cable world. All of those pairs resided together within the same cable jacket for miles before they went in different directions. They touched many, many times over the two-mile route.

I'm all in favor of keeping circuits separated as much as possible, but I truly believe that the "separate binder" thing is more of a psychological issue. We tend to associate pairs 1 and 25 as being 8" apart since that's how they end up on a 66 block. They appear to be miles apart, but they really aren't. They are still tightly bound together for hundreds of feet or even miles before they end up terminated.

Is it possible for Hi-Cap circuits or even DSL to interfere with each other in the same cable? Probably... Is this binder-specific? That is impossible. It is just a coincidence that something like this happened.

Boy Ed you really cause a guy to think. I remember the T-carrier, where transmit and receive were separated by a metallic barrier. I think the separation of groups is for a reflective type interference. As you know as well as pair twist, the groups also twist which reduces reflective interference. So there you have my theory for what it's worth. (I about wore out spell check on that one)

Great Discussion! I'm sure glad you found that box again, Ed. And yes, you've got me thinking too!

I wasn't trying to imply that interference between DSL circuits assigned to copper pairs cannot occur across binders within each 100 pair count.

However, in most instances I've experienced, interference (even crosstalk) between 2 circuits assigned to copper pairs occur between pairs within the same binder. Thus, if tested vacant pairs within an adjacent 25 pair count terminating at the same location are available, I'd assign a second HDSL to pairs within the adjacent count, versus within the same count.

With a regular 4-wire T1 being sent down copper? I'd separate the xmit and receive pairs by one or 2 vacant pairs (I know..keywords= "if available")

Bill, I know what you mean. T-Screen cable is rarely seen these days, yet it made sense for analog T1 circuits. These days, T1's are just emulated using digital circuits. I agree that on analog T1's, all of the transmit pairs should be in one compartment of the cable and the receive in the other for long-haul 4-wire circuits.

But when we have the technology to place both services over one pair, what happens? Is it a transmit or receive pair? Therein lies the question. The proverbial chicken or the egg thing for sure.