atcomsystems.ca/forum Forums Wiring - Telecom Carriers - Trunks & Services T1's, CSU's and DSU's Running good to hard loop, bad head to head?

Great site! I'm new to this site but this is a really good site. Wish I had found it years ago, it may have saved me from having to learn some things the hard way. Anyway, I know you guys have probably ran into the same situation that I am referring to. I don't fully understand why this happens and I'm sure one of you guys can explain it (I'm one of those types that has to understand the why).

I had a callout yesteday to a cell site by AT&T, reporting 2 T1's (conventional) run clean to a hard loop but not head to head. This circuit is 7 repeaters out, so I started with a quick All 0's then ran several minutes of All One's, T1-Daly, finished up with QRSS. I was running to a hard loop at the smart jack, while waiting on AT&T for a vendor meet. When we try to run head to head from the smart jack back to the DSX in the Co we get no sig, no fram, no nothing. Both T-Berds were set up correctly but nothing like it was wide open. These circuits are terminated on a Westell 3116 card. I checked the provisioning everything looked good but still wouldn't run. So a popped the modules out and plugged in my test package with a new card and it ran perfect head to head with no other changes. Turns out that it was a bad 3116 card. Can someone explain how this happens? In my feeble brain it seems that if you can run perfect with several strss patterns to a hard loop (which is going through the card to the smart jack and then back through the card to the CO) that you should be able to at least set-up on the T-berd when running head to head, errors maybe but it should setup. But this circuit wouldn't set up at all head to head.

When you say "hard loop" are you talking a looping plug or are you looping up the NID? A hard loop through all equipment would test everything, but if you're remotely looping it up your not going through all the regens in the card. That's the only thing I can think of.

A loop plug. That's why I don't quite understand this scenario. Because like I explained in the post, I am testing through the card to the smart jack, and with a hard loop it loops it back through the card toward the CO. So if I am testing through the card and back clean, why will it not even set-up head to head? My feeble brain just doesn't understand that. The T-berds were set up correctly, because they set-up good on the test package, and good head to head once we changed out the card (without making any other changes). But I'm still scratching my head on this one.

The only other thing I can think of would be frequency shift. On loop back you'd probably still sync, unless it was real bad. Head to head if the frequency wandered enough it wouldn't. Frequency shift is about the only test I can think of that's not valid on loopback.

So a bad R card (Westell 3116) could be causing frequency shift. Just curious why I wouldn't see that with a hard loop at the demarc vs. head to head? Again I had no signal, framing, or pattern while head to head. It looked like it was wide open.

Hard loops are fine for continuity testing, but that is all. The output of the NIU went open (storms?) which is why you had no pulses. As you found out, a t-1 signal will run over an open when testing to a hard loop, which is why I'm not a fan of hard loops for troubleshooting. They also don't prove if your tx and rx are flipped when doing a new install.

A hard loop is really a glorified continuity test. It doesn't verify any kind of frame settings.

Thanks for the reply, yes I agree that a T1 will run on an open tip or ring on S1 or S2, but normally I have found that you will see violations past the open or high joint. I agree you can't verify tx/rx are not transposed as well. But in this situation I am working on an existing T1 that is already in service. I got to thinking about what you said so I pinned out the demarc with a test plug and I had a 1 ohm short on tx and a 1ohm short on rx as well, so I don't believe that is the case with this particular situation. And I could be wrong but I would think if that was the case I should have violations coming back on S2 even to a hard loop. I did some further testing on the bad 3116 cards that came from that site this morning. I plugged them into my test package and wired it up at the frame to a vacant slot in a DDM+ shelf and it was doing the same thing. Run good to a loop not head to head. Change to new card runs great. The frequency was 1544001/2 & 1543998/9. I know the cards are bad I'm just trying to understand why it runs perfect to a hard loop and won't even setup at all on either end head to head. I'm one of those who has to understand in my mind what's going on with these type of issues if possible. Sorry to belabor the point but if someone could explain in further detail why the difference in the two test results it would be appreciated. I appreciate all the help so far. It has given me several things to check, but so far still not making sense to me.

Try the multi test and see if any patterns fail, unless that's the same as the Daly, never heard of that one. Also how about instead of a hard loop you put one T-berd in repeat mode and see what it does. Running to a loop that has one side of the pair open should give you bi polar violation if nothing else.

I ran muti-pat on these circuits which only run 3min each on my set, so I ran extra time on ALL 1's to test the repeater route (7 repeaters out), T1-Daly is one of the better stress patterns, it is similar to 55-Octet. It is more stressfull than QRSS, but I also ran QRSS as well.

That has been my experience as well. Also if it were open one side on S1 between the NIU and demarc you would think S2 would set up between the Berds.