FXO / FXS port configuration

Answered Question
Mar 10th, 2008

Hi all,

I'm encountering problems with a FXO / FXS configuration.

I have the following config:

CIPC --> CCME-1 --> FXO --> connected to FXS port -> CCME-2 --> CIPC

Outgoing calls from CCME-1 to CCME-2 phones are working.

Incoming calls from CCME-2 to CCME-1 phones are not working.

The call is established for 1 to 2 seconds and then disconnects.

I have configured an outgoing dialpeer on the CCME-2 router, pointing to the FXS port. Have an incoming dial-peer on CCME-1. I have also a connection plar opx on the voice port in CCME-1 pointing to the CIPC.

The voice port configuration on both sides is the default config, I did not add any commands.

I don't have any experience with analog ports.

Has someone an idea where the problem could be?


I have this problem too.
0 votes
Correct Answer by Paolo Bevilacqua about 7 years 2 months ago


Are you going through a pbx? cme-1 is getting reverse battery after connect, configure "no battery-reveral" under voice-port", or try swapping cable pins.

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Overall Rating: 5 (1 ratings)
Paolo Bevilacqua Mon, 03/10/2008 - 09:07

Hi, if you do debug ccapi you will see why the call is being closed. Don't you have ip connectivity between the CMEs ? That would let you call over VoIP avoiding use of the voice port.

Hope this helps, please rate post if it does!

d.santoro Mon, 03/10/2008 - 09:12


no I don't have ip connectivity and I have to use the analog ports.

I did a ccapi debug but couldn't see any differences to the normal call clearing.

See attachments.


Paolo Bevilacqua Mon, 03/10/2008 - 09:15

Likely CME-1 is closing the call.

d.santoro Mon, 03/10/2008 - 09:28

I have a similar debug from the other side on CCME-1.

Would you suggest to configure anything on the FXO port?

If I establish a call from CCME-1 to CCME-2 the debug shows me, even with a regular call disconnect, a call disconnect cause value = 16

Paolo Bevilacqua Mon, 03/10/2008 - 10:05

Can you talk few seconds and then it drops ?

Can you collect "debug vpm signal" on cme1.

d.santoro Tue, 03/11/2008 - 01:53

no I cannot talk for few seconds.

E.g. if I activate AutoAttendant on CCME-1 and call the number I can hear from time to time the "welc..." then the call drops. Most of the tests I do ends without hearing anything. If I forward to Voicemail I did not hear anything, the call disconnects after 1-2 seconds (based on the CIPC infos). If I forward via connection plar opx to the CIPC I see the call ringing, and as soon as I answer the call, the call disconnects after 1-2 seconds based on the CIPC infos.

I attached the debug vpm signal infos.


Correct Answer
Paolo Bevilacqua Tue, 03/11/2008 - 03:15


Are you going through a pbx? cme-1 is getting reverse battery after connect, configure "no battery-reveral" under voice-port", or try swapping cable pins.

d.santoro Tue, 03/11/2008 - 05:16


Thank you, using the no battery-reversal command the calls are now working!

And yes, the CCME-1 is working as PBX.

Paolo Bevilacqua Tue, 03/11/2008 - 05:33

Glad to know it's working now. My question was if fxo/fxs are directly connected or what is in between.

Thanks for the nice rating and good luck!



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Posted March 10, 2008 at 8:34 AM
Replies:9 Overall Rating:5
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