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

Last Saturday night we had a T-1 go down. About 2:30 a.m. the AT&T tech got it back up, but as he was leaving we found out that he had converted the circuit from a 4-Wire T-1 to a 2-Wire T-1. About 5 years ago we had problems with the 2-wire circuits and made sure all our loops were a true 4-wire. We're now having trouble getting the carrier to switch the loop back.

I'd like to get some input from our T-1 gurus about this. I plan on setting up a large simultaneous upload and download sometime this week to see how it handles the transfer.

A 2-Wire T-1! In my experience a T-1 was always defined (and tariffed!) as a FOUR wire circuit, 1 pair transmit and 1 pair receive, with a bandwidth of 1.544 mbs.

Anything else, was just that - something else.

What is this, some kind of DSL type circuit?

Sam

A follow up. (I guess I hit the "Add reply" key to quickly).

I would definitely follow up with some serious stress testing. We used to use Sunsets or T-Birds, and our routine to certify a new circuit used to be:

5 minutes of all 1's
15 minutes of all 0's
15 minutes of 3 in 24
24 hours of QRS

If it passes that then maybe it doesn't matter what it looks like. But how do you interface to it? It can't appear on an RJ-48X or a DB-15. Do they use some sort of smart jack that converts it to a 4 wire circuit for you to connect to?

Sam

That was my arguement too Sam. I claimed that this was "more DSL than T-1," but that is allegedly what AT&T is installing around here. The CLEC claims that they have no power over what type of circuit the ILEC supplies as long as the data transfer meets spec. We do have a straight line back to the cloud, and right now we're getting our synchronous speeds of 1.5, (minus reasonable overhead,) but my research on these circuits leads me to believe that when the office is full, and users are both up and downloading at the same time we're going to see problems.

To answer your second post Sam, it's an integrated T-1. It comes into a smart jack outside, then in the phone room it hands off to an IAD which breaks out the voice into analog ports and hands the data off to the firewall.

It appears to me to be more of an HDSL, but I'm finding a lot of talk on the net where people are facing the same problem with them refusing the extra pair.

From what I can find it is HDSL. Like Sam in my day a T-1 was 4 wire. So this is new to me also. From reading some about it the speed and reliability is comparable to a full T-1 span. If it's working fine I'd just make sure I wasn't still paying for a full 4 wire span. Maybe one of our CO guys can shed more light on it.

We dont have T1 here but we do have 30 channel PRI, which is basicaly a 2 meg link, they normaly use 1 pair for this circuit, but if the distance is over 2 miles from exchange they use 2 pairs circuits and re-configure the modem.

But our interface to the modem is always 2 pairs

It's definitely HDSL that comes in on one pair to an Adtran (or other brand) network termination mounting. On the CPE side of the card, it's your standard RJ48X connection with separate transmit/receive.

The PRI at my office with integrated access has been here and working for over three years with zero problems. We have a sub tenant who has his own T1 that's set up exactly the same way, also with no bandwidth problems. Verizon is using ADC Higain H2TUR402 cards for both circuits. I haven't seen circuits installed any differently around here in several years.

Ed my concern was that since you don't have a different pair for both upload and download, there would be issues when a few users are running uploads at the same time others are running downloads? I suppose a single pair can handle it since speeds of upwards of 3 Megs can be obtained on a 2 wire, but I'm having trouble with calling a single pair circuit a T-1. On second thought maybe it's that I'm having trouble paying for a 2 wire circuit that's called a T-1.

All I ever see around here are two-wire HDSL T-1's. Of course they become 4-wire at the smart jack.

Do you see them being as reliable Larry? I guess this is just something newer to this area.