Touch Tones on VoIP

I recently switched my home phone service to AT&T CallVantage VoIP. Mostly we are very happy with the results.

One problem, which I was sort expecting we might encounter is using Touch Tones. When I attempt to access my voicemail at my office from home, or use other Touch Tones controlled services, it is very unreliable.

I have tried several phones including a basic desk phone that allows long tones that generate as long as you press the button, and phones that generate a fixed length tone.

Anyone have any idea how the VoIP industry is going to address this issue?

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Its not an industry issue, its a CallVantage issue. Or more precisely, probably a bandwidth issue. I use Vonage set to use max bandwidth and have absolutely no problem with touch tone keying.

You need to check your configuration and make sure you are allocating enough bandwidth to your VOIP channel. That could be either in the adapter or the router in your house. If that doesn't work, you will need to call AT&T.

Reply to
Clark W. Griswold, Jr.

Touch-tones can be encoded one of three ways. 1) in the RTP audio itself as the dual frequency waveforms 2) in the RTP stream as an out of band token 3) in the SIP stream as an out of band token. The first is the least desirable since the tones will get mangled to some degree by any codec that isn't ulaw/alaw. The second choice gets around that codec-mangling problem but still has problems with SIP re-invites. When more than one voip server is involved in the talk path it is desirable to route the RTP directly between the voip endpoints. That gives one a snappier talk path with lower delay. Unfortunately it also prevents any intervening voip servers from seeing the touch-tones. This is why one really wants to send the touch-tones using method #3, in the SIP INFO packets. Even when the RTP is routed directly between the endpoints, the SIP packets can be routed using the long path, threaded through each server so each server gets a crack at doing something special with the touch-tones.

In my experience, touch-tones in SIP INFO packets also are the most likely to encounter bugs in the SIP server. If the voip phone is sending touch tone as SIP INFO, try setting it to use RTP tokens (aka RFC2833). If it is sending touch tones inband try setting it to SIP INFO and if that doesn't work reliably step back to RTP-tokens/RFC2833.


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Wolfgang S. Rupprecht Forums website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.