TELECOM Digest OnLine - Sorted: PRI Problems (was Re: 1A2 Help Requested)

PRI Problems (was Re: 1A2 Help Requested)

Justa Lurker (
Thu, 12 May 2005 01:03:30 GMT

>>> Our PRI between our two switches regularly goes down for anywhere from
>>> 30 seconds to 5 minutes. This seems to occur most between 8:30AM and
>>> 9:00AM and then again between 2:00PM and 2:30PM. Verizon claims they
>>> can't figure it out.

>> Clock slip?

> That's my gut feeling on it. I've tried explaining that to Verizon but
> it just falls on deaf ears.

Can you be more precise about what PRI "goes down" means ?

I guess that could be interpreted a lot of different ways.

When the trouble happens, are calls in progress affected, or do they
stay up while "new" calls in one direction or another are blocked ?

Have you monitored the PRI line at your end with a suitable analyzer
so you can see what is happening at the various layers (or does your
switch provide any detailed debugging trace) ?

For example, does something strange happen down at Layer 1 (physical
layer) when the problem occurs ... loss of pulses, loss of framing,
excessive bit errors, T-1 alarm conditions, whatever ? Do the ESF
Performance Monitoring history data show anything (I assume it is
running over a B8ZS ESF T-1 with some sort of PM functionality at each
end)? Is there a smart jack involved, and/or any LEDs to take a look

Or is some trouble occurring at Layer 2 (link layer) with the LAPD
protocol causing the D-channel to appear 'down' ?

How about Layer 3 (network layer) ... are you seeing any incriminating
result codes during the failure ?

While the problem exists, does the Verizon switch busy out your lines
to incoming calls ? Surely their 5E or DMS or SC or GTD or whatever
must maintain (or they can selectively enable) some sort of event log
for your line.

Although I suppose a timing/sync problem with clock slippage **might**
be the culprit, it's funny that it only manifests itself twice a day
rather than constantly [for severe uncontrolled slips] or at
evenly-spaced intervals throughout the day & night [for less frequent

Of course, the toughest part is getting through to talk to someone at
Verizon who even has a clue what you're talking about. If you're
lucky enough to get to talk one-on-one with one of the switch techs or
craft or engineers who can log into a maintenance console and knows
what a PRI ISDN line really is, then usually you'll make some progress
getting it resolved in fairly short order.

Finally it may be worth checking with the folks in to see what they think/suggest about your

Post Followup Article Use your browser's quoting feature to quote article into reply
Go to Next message: "Web Phone"
Go to Previous message: TELECOM Digest Editor: "Setting up an Automated RSS Feed"
Next in thread: Don Bowey: "Re: PRI Problems (was Re: 1A2 Help Requested)"
May be reply: Don Bowey: "Re: PRI Problems (was Re: 1A2 Help Requested)"
TELECOM Digest: Home Page