[asterisk-users] Zaptel ring voltage detection

[Chris Miller]

We've inherited a pair of mostly identical PBX systems, each with a 
TDM400P Rev I boards and 4 FXO modules. The production system is 
running Asterisk-Now with 1.4.9, and despite some other issues, it 
is able to answer inbound calls just fine. The replacement system is 
currently running Asterisk 1.2.28, and is unable to detect incoming 
calls, outbound calls work fine.

We discovered later that the analog lines are supplied by Cox Cable 
in Los Angeles, apparently Cox is the only telco available in this 
office building. I came to the conclusion that Cox is probably 
providing analog lines via Cable/VOIP service and that the FXS ports 
in their equipment are providing a lower than normal ring voltage.

ztmonitor shows the ring, but Asterisk 1.2 never starts a simple 
switch on the zap channel. I did find a posting from the 1.0.X days 
where someone had to lower the sample peaks in wcfxo.c from +-32000 
to +-10000, but this seems to be the standard in the current 1.2 
zaptel source (wctdm.c of course). Clearly the 1.4 zaptel driver is 
doing something different, but I'm not sure what since the values 
look the same.

We've been avoiding Asterisk 1.4 because of some serious stability 
issues we've seen in several versions. 1.4.19 seems to have 
addressed these issues, so we're likely going to deploy the 
replacement PBX with 1.4.19. Just mentioning it because I'm sure 
someone will ask ;-).

While I hope to never run into this issue again, it does raise the 
question of how could one determine the actual ring voltage, as well 
as any other analog line values that would help troubleshoot this 
sort of issue? If there are further issues with the analog lines, we 
may need the ability to detect and tweak the ring detection parameters.

Thoughts?

Chris