With the dramatic increase of calls from users/installers that have employed some sort of POTS replacement device (either cellular adapter or VOIP Analog Telephone Adapter (ATA)), it is a common report that our units have difficulty consistently interpreting the DTMF tones used for programming (and sometimes for normal operation).
There is great variability in the configurations of these devices as well as differing technologies used by SIP providers and wireless carriers alike. The default settings for these units may be fine for most voice applications, but are NOT ideal for cleanly passing DTMF tones. Follow these guidelines in order of importance for best results. (your mileage may vary!)
1. Codec/vocoder selection: G7.11a [PCMA] / G7.11u [PCMU]/ G.722 (these are the best non-compressing options for DTMF)
2. Only enable RFC2833 handling of DTMF (in-band) – competing settings or other options are less than ideal and can cause “echoing”.
3. Disable DTMF Negotiation
4. Increase DTMF Rx gain
5. Jitter Buffer – Fixed and Low setting
6. Increase DTMF duration/decoding times
7. Enable "Relaxed DTMF" if that is an option (OOMA)