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<p class=MsoNormal><span lang=EN-US>Dear core developers,<o:p></o:p></span></p>
<p class=MsoNormal><span lang=EN-US>I’ve spent another day fighting with VLDTMF
emulation code in ast_read which caused some digits to be swapped randomly and
again came to conclusion that it cannot be properly fixed in its current design.
The main problem is the AST_FLAG_END_DTMF_ONLY channel flag which indicates
that code calling ast_read is not interested in AST_FRAME_DTMF_BEGIN frames and
only wants AST_FRAME_DTMF_END ones.<o:p></o:p></span></p>
<p class=MsoNormal><span lang=EN-US>This flag is mostly used by the
autoservice. The flag is set each time channel is being autoserviced and reset
when autoservice ends. Obviously this switch can occur multiple times during
dialing because channel set to autoservice mode each time Asterisk does lookup
in DUNDi/realtime switch which can occur for each new digit dialed (in case of
Zap).<o:p></o:p></span></p>
<p class=MsoNormal><span lang=EN-US><o:p> </o:p></span></p>
<p class=MsoNormal><span lang=EN-US>Clearly, the current implementation cannot
properly handle bounces of this flag and worst of all it is really difficult to
fix. Because of this I remember about five DTMF-related issues in the last two months
and two new filled today. All of them revolve around ast_read.<o:p></o:p></span></p>
<p class=MsoNormal><span lang=EN-US><o:p> </o:p></span></p>
<p class=MsoNormal><span lang=EN-US>My proposal is to move the VDTMF emulation
code from ast_read to ast_write. This way, when application reads channel it is
not guaranteed to get properly paired BEGIN+END frames. It is not guaranteed to
get reasonable minimum duration of DTMF. And it is not guaranteed to see
reasonable gap between these frames. The good thing is that I’m not aware
of any application for which these things are important. Majority of them only need
DTMF_END frame – this is how digits pressed by the user are read.<o:p></o:p></span></p>
<p class=MsoNormal><span lang=EN-US><o:p> </o:p></span></p>
<p class=MsoNormal><span lang=EN-US>When application writes DTMF frames using
ast_write – this function will normalize DTMF. It will create missing
BEGIN frames if needed, ensure proper delay between BEGIN and END, between END
and BEGIN of the next digit etc. So at the end, Asterisk will still guarantee
that any DTMF it sends out is good. Only the “internal DTMF traffic”
may be not normalized.<o:p></o:p></span></p>
<p class=MsoNormal><span lang=EN-US><o:p> </o:p></span></p>
<p class=MsoNormal><span lang=EN-US>I believe this will simplify things a lot
(can explain why). Also I can provide more details on how I’m going to
approach if anyone interested.<o:p></o:p></span></p>
<p class=MsoNormal><span lang=EN-US><o:p> </o:p></span></p>
<p class=MsoNormal><span lang=EN-US>Any thoughts?<o:p></o:p></span></p>
<p class=MsoNormal><span lang=EN-US><o:p> </o:p></span></p>
<p class=MsoNormal><span lang=EN-US>Regards,<o:p></o:p></span></p>
<p class=MsoNormal><span lang=EN-US>Dmitry Andrianov<o:p></o:p></span></p>
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