5 replies to this topic

[elitegroups]

Hello everyone, I need some advise on how to troubleshoot those pesky intermittent sync service calls. I like when I find an obvious problem like a metallics trouble or missing/improperly installed filters. But what can I look for when the line tests good and the modem has good sync rate/high SNR? I have an Exfo 635 meter and I will do a metallics test, checking for grounds/shorts/foreign voltage/noise etc. I don't want to be blindly changing cable pairs/aerial drop wires/ dslam ports hoping it will fix the intermittent sync. In my area most of the aerial plant has been conditioned and bridge taps removed. I believe impulse noise may be culprit most of the time but how can I look for that and how to fix it. To add, I cannot spend too much time troubleshooting on these calls as I have to maintain a certain amount of calls. 2-3 hours tops is an ideal repair time. Any help would be greatly appreciated.

[Dave72]

Do you show FEC errors climbing at the customer/terminal end ? If so, then go check at the port. FEC should be at or near zero.
Your switch guys might have a log of sync reconnects that may/not show a pattern.. this might help if you are dealing with a impulse noise issue (ie, always at dusk .. then go shoot it at dusk).
Possible house power issues ? Could try a small UPS at the modem.

[elitegroups]

Sometimes the trouble ticket will say performance errors on modem end or the tester will tell me they see tons of errors on the modem side.
What does this mean? And how can it help in finding the problem. I believe my meter has a function where I can count the errors in a sync test. I guess I could do a sync tests and various points and isolate the section that gives the errors.

[Dave72]

Yes, on the Exfo you can view live errors while you sit on the line. The Exfo is a good vdsl meter, I just dont like it b/c of having to use 2 separate cables, no decent carry case etc (ie, not field friendly).. (I prefer the 3m AMS).

CRC errors, while ideally should be 0, can be seen w/o causing customer issues. The error correction system takes care of it. Once you over run the CRC system, you can start getting FEC errors. Once you have enough FEC going on, you will begin to drop packets (freezing, blocking) and even loose sync. I generally just look at the FEC.. it should be 0 over some period of time.. (longer w/o fec errors is better, but impulse /etc can cause a few.. there's no strict rule with FEC b/c then you get into Interleave also..Interleave adds delay, but protects great against FEC loss due to impulse noise.. but again, only to a point.)
If you show 0 fec at the term, do look into customer wiring and local grounding.

[elitegroups]

Thanks Dave, I will look into the fec errors for clues as to where the problem is. I must agree that the Exfo is too bulky, slow, has nowhere to store the leads etc. The shoulder strap is pathetic and just slips right off when walking. Utterly ridiculous for the field, it is best suited for occasional use.

[WoodWalkinGirl]

I have also found that if my pair runs through the same binder as circuits or T1 the noise from them can interfere with the Noise Margin on the DSL pair causing drops or loss. We had to try & test 3-4 pairs to find one that would bring it up to a 20 from a -3.5. I use a COLT 250.