[cisco-voip] Shared line between IP Phones and FXS Port with SCCP setup and CCM

[Erick Bergquist]

Hi,

We have a shared extension (2000) across 5 IP Phones and an FXS port
on a gateway for an overhead bell. The FXS port is configured as SCCP
with call manager so it can be a shared line. It works fine, and when
2000 is called the IP Phones ring as well as the bell but when a IP
Phone answers, the FXS port stays offhook until the IP Phone caller
hangs up the call. This means other calls into this extension while
they have a phone call, the overhead bell doesn't ring. We put a
regular POTS telephone on the FXS port and when 2000 is called the IP
Phones ring as well as the regular POTS phone and when IP Phone
answers, the POTS phone stops ringing but the port on the gateway is
offhook still. When we lift the handset on the POTS phone it is just
dead air/silence and no one can hear.

When the port is configured as MGCP, when the IP Phone picks up the
call the FXS port goes idle and a 2nd/3rd call into the line ring the
FXS port fine but with MGCP after awhile the port gets hung up due to
a bug but when we try newer IOS versions where that is supposedly
fixed the FAX calls stop working due to other bugs.

Just wondering if SCCP should act as same as MGCP with this shared
line scenario, and why with SCCP the port stays offhook after another
phone picks up the call to the shared line.

The gateway is a 2800 with a VIC2-FXS and we've tried IOS 12.4(11)T
through 12.4(20)T with same problem on CCM 5.1(3) and CCM 6.1(2).
Again, with FXS port configured as MGCP the port goes idle after
another phone picks up the call on the shared lines.

This is what the FXS port state is after another IP Phone answers the
call on the shared line, with a regular POTS home phone or the
overhead bell plugged into it.

Gateway#show voice call summ
PORT           CODEC     VAD VTSP STATE            VPM STATE
============== ========= === ==================== ======================
0/1/0         g711ulaw   n  S_SETUP_REQ_PROC      FXSLS_WAIT_OFFHOOK