atcomsystems.ca/forum Forums Wiring - Telecom Carriers - Trunks & Services T1's, CSU's and DSU's Trouble shooting tips?

Well guys, dumb ole me again with some tech questions. I am trying to wrap my mind around troubleshooting HiCap circuits from within a CO environment. Are there rule of thumb areas to look for for certain errors. For example on a T-1 circuit if I am taking Bit errors and I have narrowed it down to coming from my Co, now what? Where should I look, I mean are bit errors most likely caused by equipment, cabling, provisioning, timing...
I am trying to narrow down possibilities, I mean if your car shakes when you drive it you know to look somewhere in the drivetrain and tires not necessarily for how much gas is in the tank. Can I think the same way with errors?
What about CRC errors, what is most likely these caused by? I have a million questions if someone deosn't mind me emailing them instead of these postings.
Thanks in advance......

Google "loopback plug" or "loopback jack" Either buy one or make one. The problem is either your equipment or the C.O.s. If you think it's the C.O.s then call up your carrier and tell them. A loopback will give you an indication if it's working good or not by you making it talk to itself.
A million questions and answers are not necessary. Troubleshooting 101 says "Isolate the problem".

Maybe I misread your original post. Are you saying that you are IN a CO?? ---- "I am trying to wrap my mind around troubleshooting HiCap circuits from within a CO environment."----.

Yes sir, I am in the CO and have looped circuit back to my CO to prove it is in my office. I do not currently have these trbls, I was just wondering if there was certain errors that could, as a rule of thumb, be associated with circuit packs, the cabling between equipment, timing issues....As I understand it if my Dsxdb levels are off it would be a indicator to check wiring ( jumpers, coax...)

I am trying to develop my troubleshooting skills by trying to learn from all of y'alls experience ( if you are willing to share it with this board) Not wanting someone to take me by the hand and fix it for me, just point me in the right direction.

If you can find a Tberd manual they are a pretty good source for error explanation. Off the top of my head. BPV's indicate errors in hardware or wiring. CRC's noise on the line or framing mismatch with little traffic. Failure of all 1's bad repeater. Slips timing, usually CPE, in theory source can't slip. That's about all I've got without looking stuff up.

If you're troubleshooting a copper circuit, go to the C card and pull PM data off of it to a laptop via serial port. After some practice you'll be able to get a pretty good idea where your trouble is coming from.

Someone *should* sit you down and walk you through it the first time around, laptop in hand, step by step. It's not rocket science by any stretch of imagination, but it does require grasping a few basic concepts.

Adtran had some great manuals regarding HDSL technology for both CO and field use, try to locate some of them.

Bill's suggestion on reading through T-Berd manuals is an excellent one as well.

Once you properly understand the concept of circuit design, you'll learn to troubleshoot from different points, and ability to properly interpret PM data will prove to be very important.

For the record: I'm not a COT/carrier tech/frame guy - but the dude "on the other end", staring at a blinking R card...LOL...

Don't forget to have fun while learning this stuff. Seriously. It can be pretty amusing and entertaining if you don't stress yourself blind over it.

My $0.02 only...

I would be glad to help you. I am a retired instructor and taught both CO and outside technicians in various transport technologies.

nightntwktech,

It is important to keep in mind that their are various forms of a T1. You have to keep that in mind when you troubleshoot them.

A conventional T1 is made up of an office repeater, line repeaters, better named line regenerators,a Smartjack, aka NID, Network Interface Device, NCTE Network Channel Terminating Equipment, NIU, Network Interface Unit.

A conventional T1 has limited Performance Monitoring capibilities because the office repeater the line repeaters and the smart jack are usually made by different manufacturers and there is no common "language" for them to speak.

Soneplex and Adtran HDSL T1's consists of a C unit in the CO and an R unit at the Remote or customer. It may or may not have a line regenerators called "doubblers" because they double the distance the circuit can be deployed. Because each is made by the same manufactuer, they talk to each other constently and gather Performance Monitoring Information for use in OAMP or Operations, Administration, Maintenence and Provisioning.

Line coding:

Conventional T1: Bipolar pulses AMI. Alternate mark Inversion.

Soneplex HDSL T1: 2B1Q

Adtran T1: Started out with TC Pam and in the new versions 2B1Q (because Adtran bought out Soneplex from ADC).

The type of T1 your dealing with will determine what tests you perform, what impairments to look for.

John,

Does 2B1Q = B8ZS ?

I've been installing T-1s for quite a few years, and have never heard of term "2B1Q"...

Sheer curioisity on my part.

Always willing to learn from older and wiser cats...

2B1Q = 2 binary one quadnary. Simply put: For a voltage of +1 volt it equals the binary code of 00. +3v = 01. -1 volt = 01 and -3 volts = 11.

So an 8 bit byte or "word" can be represented by 4 voltage level changes.

In effect the frequency of an HDSL T1 is reduced to 1/4th that of a conventional T1 allowing it to be deployed 12kft without regeneration. A conventional T1 must be regenerated at 6kft intervals.
PS: dont quote me on the volts vs bits I'm trying to do it from memory.

B8ZS = Binary eight zero substituation.

It only really really means something to a convential T1.

The requirement calls for a substituted special pattern to be inserted and transmitted in the case where 8 zeroes in a row are supposed to be transmitted on the T1.

Digital circuits do not like to see zeros, it screws up timing and syncronization circuitry of regenerative sections of equipment.

8 7 6 5 4 3 2 1 Bit position

0 0 0 0 0 0 0 0 T1 is suposed to transmit

0 +1 0 +1 -1 0 0 -1 substituted bit pattern

There are deliberate Bipolar violations in the 4th and 7th bit positions which tells any equipment capable of detecting BPV's that this is a substituted bit patteren for 8 zeros and don't flag it as a BPV.

At the receiving end the substituted pattern is removed and the 8 zeroes are reinserted.

At the receiving end the substituted pattern is removed and the 8 zeroes are reinserted.

The T1 will transmit in a Bipolar (AMI) format under normal operation. If 8 zeros are to be transmitted the trannsmitter will insert the substituted B8ZS pattern until such time that the transmission of 8 consecutive zeros ends. Then it returns to sending in the Bipolar (AMI) line code format.

OK, you lost me here and I'll tell you why:

When you have a B8ZS transmission from the A-end hitting into a mux at the Z-end where the low speed card (or C card depending on the mux design) is programmed for AMI, you'll take errors and there's one pattern - I forgot whether it's 1:7 or 1:8 - that won't run. QRS will run with no issues. I've learned this the hard way...let me just add that the circuit was designed (in both cases that I've seen) as a HDSL in the field. My take would be that when the switch on the low-speed card is incorrectly set, I don't believe that the type of C card used really matters - be it a H2/H4 HDSL one or the conventional "full" T-1 card...

I'm *not* questioning your knowledge - way too green for that - just trying to understand what you were trying to say...

I think your getting deeper into theory than you need to to trouble shoot T-1 troubles.

I've only worked pure 4 wire T-1's so know nothing of this new stuff, yet the basics would still be the same.

When you are talking low speed cards you're talking about breaking a T3 down to the T1 level and I don't think that's where John's going. I do think John knows what he's talking about, but just don't think you need to be that deep into it to trouble shoot T1 problems.

The biggest problem with low speed cards, at least in my experience, is when the T3 resets, or high speed card is changed, the default is AMI on the low speed. As you know AMI won't pass B8ZS, but B8ZS will pass AMI. So why didn't they make the default B8ZS? $$$ is the only reason. They want the customer to pay for privilege of running B8ZS.

Learn the basics the hard stuff you'll pick up as you go. The vast majority of your trouble will fall into the basic category.

The only time we installed AMI was on voice-only (56K) circuits. It was explained to me at the time that because these circuits were simpler, they were also more robust, which is what voice managers wanted.

Data circuits (full 64K) ran B8ZS. Data managers wanted to be sure that the data came through immaculately.

All 1s should run on anything. All 0s will only run on B8ZS. QRS is not designed to test the data carrying capabilities of a circuit, rather it's designed to troubleshoot physical plant. When I would get failures on QRS I would look to the cross connects, the wire wraps, the patch cords, the jacks - that sort of stuff.

Like Bill I have no experience with 2 wire circuits. I would echo what he said - learn the basics and the hard stuff will come. Pay attention and take notes.

Sam

Adtran and HDSL T1's scramble the transmission such that there is never 8 zero's will never be transmitted.

"Pay attention and take notes"
There is no one for him to pay attention to or take notes from. They are all gone. Either retired or pushed out the door with Supplimental Income. His situation is typical of the modern telco technician inside and outside! They will only teach him enough to get by until such time he becomes expendale.

The subject was T1's not muxed circuits. I'm only talking about T'1s leaving his CO to a smart jack and the different techniques.

I wish I were closer to WI, because for this statement alone - all of your other contributions nonwithstanding - you earned a dinner and quite a few drinks from me...

Thanks once again - Bill, Sam and obviously John - for reminding me how much I still have to learn after a decade of doing this stuff...

To OP - good luck. Bookmark this thread and visit it often...

Keep the questions coming!

John, if the OP is running trouble on HiCaps there would be no end user. Unless the term HiCaps has changed since I retired. It's a DACS to DACS type circuit between two offices, usually a long haul and local office.

That's why he mentioned the MUX's. I doubt he even touches HDSL. We'll have to hear from him to be sure though.

From his original post:

It sounded like he wanted information from the DSX to the equipment side of the repeater, out the facility side to the cable pairs, which his responsiblity. If he wants to trouble shoot the office in he must do as you say from the low speed card channel DSX towards his mux

To all THANKS for these tips, hope many more are to come. My responsibities as a CO tech are from the incoming signal, whether it is generated in my CO , or incoming from a IXC ( AT&T, Sprint, CLEC...) through my office. The signal path might be all DS0, DS1, DS3 or up to any optic levels OC 3 through 192 and yes this does include HDSL. This includes any and all MUX's, DCS's, fiber jumpers coax's the whole path in my office. So you can imagine all the different errors and troubles I potentially can encounter. I am just very glad I found this site for advise from techs who have been in my boots...

Now you tell us!

To OP:

Whenever in doubt, just scream "trouble out" and deal with whatever comes back... :rofl:

No.........Please do not scream "Trouble out" if you not in fact sure the trouble is out. I work outside and it is very frustrating to chase ghost trouble on the outside, especially if its a span with with 10-18 repeaters on it. You guys in the co have a frame to find a problem on......we techs outside have many miles of crappy plant to chase.....please dont cry wolf if there is no wolf

It's not called crying wolf...where I am (and I'm a field tech as well) we refer to it as "job security"... :toast:

All jokes aside, most of today's inside folk cry wolf when uncertain, while the outside forces claim the wolf is inside the CO when they don't feel like dealing with the aforementioned garbage once known as copper plant...

I agree with the job security aspect....I just don't like it when they cry wolf at night and then I get a callout at 1am....

Well...that's where the $$$ is in our line of work... :shrug:

Shortly after "Divestiture" of the Bell system and please forgive me for continuing to reference it, but to us Bell Heads, our world changed for the worse after it, we started hearing the phrase "when in doubt dispatch out" from the testing technicians. In the old days the tester would have to be 10000000% sure the trouble was "out" before a dispatch was requested.

John,

Nowadays it's "even when not in doubt dispatch out"...

Let me share a piece of my (fairly typical) workday from yesterday...

The customer in question reported trouble on 4 PRI circuits. Trouble reported " a 5 second delay before the line rings on the other end ".

Their IT guy (who knows me pretty well at this point) greeted me with "what are you doing here?"

Exactly.

Had anyone bothered to spend 30 seconds actually reading the trouble report, the ticket would've gone right to the switch which is where I sent it...after wasting time to prove that we could run clean "all patterns" to smart jacks on all four circuits...

One easy Saturday for me. But it doesn't make it right...

"Had anyone bothered to spend 30 seconds actually reading the trouble report"

This happens every hour, every day, everywhere, throughout this country. Take some degree of solace in knowing that yours is not the exception but the rule.

Did thet ever find the cause of the 5 second delay?

Got fixed in the switch, as per the customer...the trouble's gone.

What do I know?

I've seen this happen if the customer or telco were performing a software upgrade and missed an option.

With the company I work for I am responsible for all the above as well as installing and maintaining our t1's to our pairgains in the field as well as the associated dslms. We also install and maintian all of our T1,HDSL,GigE etc.type circuits from the Co all the way to and including the customer prem. We install test and turnup every circuit. In other words they have made us a jack of all trades and a master of none.