[Asterisk-Users] False RING (incoming call) on Digium X101P FXO

[Steve Haehnichen]

I have a normal backup phone (and an alarm panel) sharing the POTS
line with the Digium X101P FXO:

     |
     |
Wall |>---+------X101P FXO as Zap/5
     |    |
     |    Phone & Alarm

Whenever the Phone is used, Asterisk sees a 'false ring' signal
immediately when the phone is hung up.

The Alarm panel dials out nightly at around 1AM, and each time it
completes the call, Asterisk sees another False Ring.

As you can imagine, this is rather annoying, since the bogus ring
causes Asterisk to kick off the incoming context (pots-line) and ring
the inside extensions.  It looks like this:

ERROR[294930]: File callerid.c, Line 192 (callerid_feed): fsk_serie made mylen < 0 (-12)
WARNING[294930]: File chan_zap.c, Line 4317 (ss_thread): CallerID feed failed: Success
WARNING[294930]: File chan_zap.c, Line 4334 (ss_thread): CallerID returned with error on channel 'Zap/5-1'
  == Spawn extension (pots-line, s, 1) exited non-zero on 'Zap/5-1'

Clearly there is no CallerID because there was no actual ring signal.

Why is the FXO seeing a local hangup as a Ring?  I thought Ring was
90v AC.. not something easily mistaken.  The hangup is just one pulse.

I have tried both kewlstart and loopstart with the same results.  This
is a standard U.S. (Southwest Bell) line.

What else can I try?  Is there any way to 'tighten up' the ring detection?

-Steve