[Asterisk-Dev] TDM400 answering POTS voicemail polarity reversal

[Rich Adamson]

> I have a TDM400 with FXS and FXO modules.
> I have one POTS line attached. Real inbound calls get correctly
> answered and everything is good and it works as expected.
> 
> But several times a day asterisk gets a polarity reversal event and then
> a bad caller ID and it answeres the call (well, it starts the dialplan).
> There was no ring detected by asterisk but it answers the call anyway.
> There was no ring on the line as other devices did not detect a ring.
> 
> The POTS line has voicemail from the telco. It seems that when telco
> sends a voicemail message waiting signal asterisk sees that it should
> answer the call, even when there was no ring.
> 
> The mystery "calls" were an hour apart to + or - 2 seconds. Not a random
> thing. When I deleted the waiting telco VM the random call answering stopped.
> But it was not EVERY hour, so it's not a 100% consistant problem, but
> it happens several times a day...when there is VM waiting....
> 
> I'm using SVN 1.2. Should I open a bug or is this a know issue? I can't
> seem to find a bug about this problem. I guess a feature could be added
> to understand and read the telco POTS message waiting signal.
> 
> Yes, I know VM from the telco is bad, but it's on the line already....

This is likely a config issue and probably should be posted to the -users
list.

The issue is likely related to the telco's VM notification in the form of
either line reversal or stutter tone. When using your pots phone, what was
the indication that you received on the phone when someone left a VM?
Or, was there an LED that would lite when a VM was left?

One thing to try is to add this to zapata.conf:
 busydetect=yes
 busycount=6
to see if that impacts the issue.

Also, if your rxgain in zapata.conf is set too high, * might be detecting
noise on the pstn line (in the form of line reversal, stutter tone) that
it thinks is ringing. Try reducing the rxgain value to see what impact
that might have.

Note that any changes made to zapata.conf requires asterisk to be stopped
and restarted (a reload won't cut it).