Resolution
If the Foreign Exchange Office (FXO) connects to a Foreign Exchange Station (FXS) port on your PBX or Public Switched Telephone Network (PSTN), and the telephony devices are not receiving Dual Tone Multifrequency (DTMF) tones from the router's FXO port, ensure that the dial-peer voice pots command is configured to forward digits.
By default, the router or gateway matches and strips exact destination patterns.
This is an example:
!
dial-peer voice 1 pots
destination-pattern 123
port 1/1/1
!
In this example, the router does not pulse out any digits on 123; therefore, be sure to have the correct prefix or forward digits configured for forwarding the desired digits. For more information, refer to the Digit Stripping on Outbound POTS Dial Peers section of Configuring Dial Plans, Dial Peers, and Digit Manipulation.
If you have the correct Plain Old Telephone Service (POTS) peer configured, and you are still not receiving digits, make sure that the router is sending the correct DTMF tones by issuing the debug vtsp dsp command and making the call while capturing the logs. This log indicates each tone with a few lines of text, including a digit=1 as well as exact frequencies of the tone. If you see the correct digits pulsed out, then the router is sending the digits, but somehow the PBX or PSTN is not receiving them.
In this case, you need to check values on the other end of the wire with a T-berd or analyzer. If you see duplicate or missing digits in the logs, this could indicate a problem with Digital Signal Processors (DSPs) or incorrect digits received from the originating gateway. If the frequencies of the digits are not recognized, then the correct tones cannot be pulsed out. Make sure you issue the dtmf-relay command on the dial peers, especially if you have a very low bit rate codec configured.
For more information, refer to Common issues with the analog FXO and FXS circuits.
