Cisco Support Community
Community Member

MGCP FXO issue


I have an MGCP gateway with 4 FXO. Only 2 FXO er connected to Telco lines.

One FXO/Line hehaves very normally. However, When I call the num asssociated to the second FXO the attendant internal IP phone keeps to ring one time then stops , then rings one time again , then ring one time ,.... continuously.

I can't see any prob in the config and the debug commands output

The caller hears a continuous (normal) ring.

Any suggestions to resolve this.

best regards,

Community Member

Re: MGCP FXO issue

If you disconnect the POTS line and connect it to a test phone set does it behave normally?

What if you switch it with the first FXO, same behavior?

Community Member

Re: MGCP FXO issue

How did you resolve this issue?

Community Member

Re: MGCP FXO issue

Same issue here, any resolution?  I will post if I get this figured out.


VIP Super Bronze

Re: MGCP FXO issue

If someone has an SDI trace (Detailed level) from UCM showing the MGCP and SCCP signaling of this; and/or an output from the router with the following debugs, it would help us narrow this down for you. Please include the gateway and IP phone addresses involved in the example.

debug voip ccapi inout

debug vpm signal

Also, is this a loop or ground start FXO circuit?

Lastly, I'm not positive that I follow the original description here. Please confirm whether this is accurate or not:

  • Calling party hears normal ringback.
  • Called party phone rings once and then stops
    • Does the call disappear from the phone entirely or just stop ringing?
Community Member

Re: MGCP FXO issue

I will get the debugs and post tomorrow.  I can confirm the experience.  The caller hears normal ringing, the Called phone does a half ring then disconnects, and does this until the caller disconnects.


Community Member

Re: MGCP FXO issue


Most likely it is a telco issue on the pots line, which was the issue for us

Swap the two FXO port lines, The problem will follow the pots line.

The verizon tech mentioned there was a crossed pair outside the facility.

Good Luck

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