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Re: [Linphone-users] DTMF not working any more on iPhone?

From: Simon Morlat
Subject: Re: [Linphone-users] DTMF not working any more on iPhone?
Date: Thu, 05 May 2011 23:25:00 +0200


I did a test this morning with lastest 1.0.5 release (published two days
ago on appstore) and dtmfs were working fine. I did the test with
Can you try again after the update ?
For your information, the choice of codec has an impact on whether dtmfs
are transmitted.
To summarize, (and I hope I'm not going to confuse you too much with
technical terms):
1) when the server supports "telephone-event" audio payload, dtmfs are
sent using the RFC2833 encoding, which is very reliable.
2) if the server does not support "telephone-event", then it depends:
->if pcmu or pcma codec are used for audio transmission, then DTMFs are
modulated in the signal (sometimes unreliable but this works most of the
->for all other codecs nothing is transmitted, because it simply cannot
work, the other codecs being unable to compress/uncompress DTMFs without
heavy distorsion.

As a consequence the reliability of DTMF transmission depends on the
server support for telephone-event encoding, and in other case on the
choice of the codec and the quality of the network layer (with packet
losses, dtmfs can be splitted in two or erased...).

Best regards,


Le mercredi 27 avril 2011 à 17:50 +0200, Xavier Nodet a écrit :
> Hi,
> I'm using Linphone on my iPhone 3GS (iOS 4.0.1) since a few months,
> and upgraded two days ago to version 1.0.4.
> Since then, I can't use DTMF servers any more.
> Although I hear the tones in my earphone when I press digits on the
> dialer, it seems those sounds are not transmitted (or incorrectly) to
> the other party.
> I tried two different servers, including one that I use almost every
> day: it does not recognize the tones any more.
> Do others experience the same issue?
> Thanks.
> -- 
> Xavier Nodet
> _______________________________________________
> Linphone-users mailing list
> address@hidden

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