SPA303 DTMF settings not per manual

[Neal Unitt-Jones]

DTMF for in-call applications does not work on my SPA303. The receiving computer cant 'hear' the tones.

The online manual says there are two options - In-Band and Out-of-Band (RFC-2833), and goes on to recommend Out of Band. But the config utility has 6 options

1. In band
2. AVT
3. INFO
4. Auto (defualt)
5. In band + INFO
6. AVT + INFO

At the very least the manual shoud reflect the utility - however, my questions are;

1. Assuming AVT = Out of Band, do I select with or without INFO (whatever that is)?
2. DTMF Tx Volume for AVT Packet: 0 (defualt) - Manual does not mention. Is this OK?
3. DTMF AVT Packet Interval: 0 (default) - Manual does not mention. Is this OK?

For info: Preferred Codec: G711u (default)

I an a noob and barely understand any of this. Have researched forum and manual before posting.

Thanks

Neal

[Dan Lukes · Accepted solution]

There is one in-band and two out-of-bands method (AVT and INFO). Also, it's possible to send DTMF using two methods at the same time. It results in 6 options you mentioned.

Now your questions:

1. you should prefer method supported by your voice provider. The "auto" works correctly in most of cases.

2. Is documented in Appendix A of Administrators guide. Don't miss the notice related to gateway compatibility issues. Ask VoIP service provider for value suitable for it's gateway. Try a nonzero value if no informations are avaiable.

3. It's undocumented option. Leave default unless instructed to change.

According codec used - it's beeter to avoid transcoding if possible. G711u is preferred in North America while G711a is used in Europe. Use codec preffered in country of voip provider you are connected to.

[Neal Unitt-Jones]

Thanks Dan,

The problem initially got worse/better! Some automated systems could hear my DTMF, others could not. Agggh!

My provider is freespeech.co.uk

1. For DTMF type they say "via audio". I assume that this is in-band. However, I have set to "Auto" as you suggest.

2. and 3. AVT settings therefore now not an issue.

The Codec setting G711a worked. My provider is in the UK.further research found their recommended codec G729A - that works too.

This all shows that the information is out there somewhere, but we need people like you, Dan, to help us know what we are looking for.

Neal

[Dan Lukes]

Some automated systems could hear my DTMF, others could not. Agggh!

Those issues are often caused by protocol transcoding on inter-operators gateways. Then, some automated systems located behind operator's interconnect A may work, while others, located behind interconnect B may not.

Only your operator may help you in such case.

According DTMF type - glad to hear you trusted me, but operators advice should be always preferred over my advices. Yes, "via voice" is in-band.

According G711a versus G729A code ...

G711a is uncompressed codec with best MOS (quality score). Moreover, it's codec supported by any operator oncluding classic European's public telephony. Thus no transcoding necesarry on the path. But G711a require a lot of bandwith (about 80kbps). As long as your connection can take it it's the codec of first choice.

G729A is compressed codec with slightly lower MOS. Transcoding is mandatory for calls relayed to public phone network or other networks not supporting the G729. Compression as well as transcoding cause audio distortion. If you line can't take G711 bandwith then G729 is best choice for you.

Try in-band DTMF with G711a then in-band DTMF with G729A. It may help you to reach most of automated systems.

[Neal Unitt-Jones]

To anyone searching for DTMF issues and finding this thread. Even with the settings per the help on this thread the problem would come and go. I found a practical solution. Pick up the handset before dialling. I prefer to use handsfree, but the tones sound very loud, if I un-cradle the handset, dial into a conference call for example, then switch to speaker it works.