"Failure to communicate" problems

[tourman <robercampbell@xxxxxxxxx>]

Perhaps some of the regulars can suggest a solution to a problem I'm
having.  For years now, I've been having random failures to
communicate that are not caused by improper programming of the panels.
There seems to be no pattern to them that I can determine, nor is it
make specific. The station is no help and insist there are enough
lines coming in to handle any amount of traffic. Whenever they happen,
I have the client send a manual test through to the station, and it
always goes through properly. This only seems to occur with
conventional land lines

I get daily reports and every day, and there is at least one panel
that doesn't seem to have communicated it's test signal (out of a base
of 1100 accounts). When I check, rarely is it a real problem....

Can anyone familiar with station technology suggest potential
solutions/problems that could be occurring. I'm at a loss...