[Asterisk-Users] TDM400P FXO channel remains Offhook after outoing or incoming call / line is parallel with other telephone equipment

[Andrei (MPI)]

Hi,

I am preparing to roll out Asterisk setup with TDM400P, 4 FXO modules in 
a small office. Asterisk will replace legacy system (4 telco lines, 8 
extensions PBX), but before the new system and ip phones would be 
installed, the legacy system is still in use. The four telco lines are 
now connected in parallel both to legacy PBX and the 4 FXO modules in 
TDM400P. Asterisk is configured not to pick up any incoming calls.

zapata.conf:

signalling=fxs_ks
musiconhold=default
languages=en
context=inbound-analog
group = 1
channel => 1-4

zaptel.conf:

loadzone = us
defaultzone=us

fxsks=1-4

I am dialing out via Asterisk and it works fine untill the following 
situation:

- one of the telco lines occasionally becomes mute after call is 
completed, would not provide dial tone, (not sure about ringing on that 
line) - both via old and new PBX.
- zap show channel <n> would show that line as 'Offhook', though no 
telephone is off hook.

If physical line would be unplugged from TDM card, the line would become 
normal again.

Sorry, if it is a well known problem, but I did not find any specific 
information yet.. Please answer two questions:

 - is it really bad to have parallel connection on TDM400P FXO lines to 
an additional telephone equipment, does it prevent TDM400P to detect 
Offhook/Onhook correctly?
 - will the problems go away when parallel lines would be disconnected 
(legacy PBX shut down)?

As you may understand the office personnel has anxiety that this may be 
a bad Asterisk setup / bad TDM card etc (which I am sure so far that it 
is not).

Please help.

Sincerely,
Andrei