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

OK one of you CO Mike types. (Like Trace said) Any difference in trouble shooting these?

No real difference troubleshooting them. We don't do anything differently for looping and sending patterns across them. Effectively there is no difference between them. The 2wire and 4wire only refers to the span between the HTUC card in the office and the HTUR card at the site.

Thanks. I assumed that was the case, but we all know what assuming can do.

One notable difference is that there are no repeaters on HDSL circuits. So in that sense, they provide one less point of failure over a traditional 4-wire T1.

In the Chicagoland area we refer to the AT&T Techs.that service these circuits as "DOGS",
as they are in the Digital Operations Group.
I've often heard them refer to the single pair T1
as a "high voltage T1", I have no idea why as it's not like the old Western Union Trunks that could knock you on your butt.
I do know that when bundled with DSL it can knock out the DSL. We found that out the hard way when they ran a single pair T1 through the same 25 pair UG that had several DSL lines in it.
This was to a small strip mall.
Had to set up a vendor meet.
Disconnected the T1 at the CO and the 3 DSL lines came back up, tied it down the 3 DSL
all went out again.
Changed the T1 to a 2 pair all was happy.
It was an old time Tech. who suggested this as he had seen it before.
The CLEC, (XO) claims it's cheaper for them to use the single pair where they can, I'm not sure if this is true but I was also told by the AT&T Tech. that they do have to be fairly close to the CO for them to use a single pair.
I thought all this was interesting until it cost me 2 days screwing around on my time.
---------------------
MrG

Good points... True there are no repeaters on the circuits, but they do have something very similar called a doubler. Same beast that does the same thing, just works differently.

What they are referring to as "high voltage" means that there is "span" power on it. Off the top of my head I'm going to say about 130VDC. Pretty hot and will knock you on your butt. Distance from the CO for these is not really an issue because of the doublers. I've seen circuits that had 5 or 6 doublers on them.

As far as the cost, I don't think there is a price difference on the circuits. IMHO, it's just a matter of preference or availability of pairs or equipment for the carrier.

The term “high-voltage” is referring to T1 that has a repeater. The voltage is for powering the repeater in the span.

The circumstances you talk about in knocking down ADSL service, was exclusively a problem when trying to REPEATER 2-wire HDSL loops. It has since been determined that if loop length is too great to reach the H2TU-R from the C.O. with 2-wire, (roughly 9 Kft of 26 gage) then using a repeater is NOT an option. (Adtran actually discontinued producing the H2RE ADSL2 repeaters for this reason.) Adtran has since developed and starting producing the 3rd generation of HDSL … HDSL4 which can reach farther and be safely repeatered.

Here’s a quicky look at HDSL technologies out there:

1st generation:
HDSL
4-wire loop
Max loop length 9 Kft of 26 ga. or 12 Kft of 24 ga. without being repeatered
HRE repeaters can interrupt ADSL signal in the same binder group if the ADSL loop is greater than or equal to 10.5 Kft.

2nd generation:
HDSL2
2-wire loop
Max loop length 9 Kft of 26 ga. or 12 Kft of 24 ga. without being repeatered
H2RE repeaters can interrupt ADSL signal in the same binder group if the ADSL loop is greater than or equal to 10.5 Kft.


3rd generation:
HDSL4
4-wire loop
Max loop length 12 Kft of 26 ga. or 16 Kft of 24 ga. without being repeatered
ADSL spectrally compatible with repeaters.

Span power on Adtran units is 190 vDC.

I’m in the position where I’m the one to choose what T1 technology is deployed on a per circuit basis in my areas for the lil’ ol’ LEC I work for… I ALWAYS try to use HDSL2 first if it’s an option. That saves a pair (which is a huge deal) and with only one pair, it halfs the probability of a pair going bad.

As far as what the hardware costs… The HDSL4 is slightly more expensive per unit, so that’s another win for HDSL2 when is a viable option.

Hey Trace now you know who to call when you have problems. Good information guys, thanks. :thumb:

That's exactly the same thing I was thinking. Trace not only got a bunch of good answers, but he asked for the time and learned how to build the watch. Good job with some really high-quality answers gang.