Grandstream 486 and DTMF Tones

I'm having problems with DTMF tones.

I have a grandstream 486 ATA using "PCMU" as my codec.

If I set DTMF to be RFC 2833 then Voipfone recognises my tones and I can access voicemail and other functions within voipfone. However, in this mode I cannot phone callcentres etc. where I have to use tones to access menus. The tones are not recognised and if I phone my mobile number and listen to the tones being sent they sound clipped and distorted.

If I set DTMF to be in-band then call centres work fine but then Voipfone themselves don't recognise my tones.

Any suggestions as to what the answer is? I did try SIP but this seemed to fail for callcenters as well.


I've been thinking about this problem some more.....

If I use RFC2833 then the DTMF tones from my phone get converted into special messages in my ATA to be sent over the internet to voipfone. When they get there they they correctly operate the voicemail system so it would appear they are being generated correctly at my end and then received and decoded correctly at the voipfone end.

If I phone my bank (I've been testing with Virgin Money as they have a free fone number!). Then I presume these messages get sent as RFC2833 to Voipfone (which we know already works) then at the point where the call is injected back into the PSTN system to go to the bank there has to be a DTMF tone generator somewhere at voipfone to put the tones back into the audio signal.

How come this works for some and not for others?

Problem Solved!

I've finally solved my DTMF tones problem.

I checked the grandstream website and found there was a software update for my device (HT486 rev 2 - sometimes referred to as HT487).

I've installed the new release and now in the DTMF options list I can select both in-band and RFC2833 at the same time.

Now I can send tones though to the automated call centres and I can access the voipfone services.

I'm still puzzled as to why voipfone don't convert RFC2833 messages into in-band DTMF when call leaves the IP world and enters the PSTN world - any ideas out there?


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