[comp.dcom.telecom] Troubleshooting Failed Calls From a PBX

Alan Gilbertson <Alan.Gilbertson@f230.n3603.z1.fidonet.org> (05/17/91)

Forwarded from FidoNet's MDF echo by Nigel Allen (ndallen@contact.uucp)]

A piece of troubleshooting just completed here may be relevant for
other telecomm managers who run into this situation: suddenly a
percentage of calls from a PBX to local telco CO (as opposed to calls
routed direct to an IXC) return "Your call cannot be completed as
dialed" or "Your long distance company cannot complete your call as
dialed" (when the number dialed was a local call.

At least some cases, adding CLASS services eats up processor time and
increases the time between a ground flash acknowledgement to the PBX
and the attachment of DTMF receiver/register in the CO.  If the PBX
begins sending digits too soon, the CO can miss the first one or two.

I had never seen this particular problem until relatively recently,
when users began reporting a high percentage of apparent misdials,
particularly during high local traffic periods.  The start of the
problem coincided with the introduction by the LEC (GTE in this case,
using a GTD5 end office) of some new CLASS services.

Increasing the pre-dial delay on outpulsing from the PBX completely
handles this, needless to say, but it was a mystery for a week or so
until we were able to correlate the dates the trouble began and the
introduction of the CLASS services.


Alan