[Asterisk-Users] Polycom DTMF

[David Gomillion]

Problem:
   Polycom SoundPoint IP phones (running SIP) ceases to send DTMF that
Asterisk can detect and use.  It worked in 1.0.5, but has not worked
since.  This has been verified on SoundPoint IP 300's and SoundPoint IP
600's.

Workaround:
   It used to be that for DTMF to work, I had to set the mode in
sip.conf to "inband".  Without making any configuration changes on the
phones, I changed the DTMF mode to "rfc2833".  The DTMF is recognized.
No reboot to the phone is necessary, and remember that you can reload
the sip configuration with a reload in Asterisk, meaning your PBX
doesn't have to be restarted either.

Discussion:
   This is probably not the "right" way to fix this, as Polycom's
configurations, by default, will "encode DTMF in the active RTP stream".
There may have been a change in the sip channel's code that is causing
this.  Others on the list have indicated that they worked around the
problem by reverting the version of the sip app to an older version.
   As the new code usually fixes other problems, the solution of
reverting seemed to be counter-productive, so I tried other DTMF
signalling modes.  Thankfully, the stock Polycom configs will work with
Asterisk's sip.conf "rfc2833" DTMF mode, at least as of
CVS-v1-0-03/23/05-21:40:48.  When I get more time, or if someone else
has the time, an examination of what changed to cause this could enable
us to fix the heart of the matter.
   Other users on the Asterisk list (see thread "*-1.0.7 DTFM => Not
working" from 03/23/2005) have reported other UAs not working.
Therefore, there may be a bigger problem with the fundamental issue at
hand: when do we change DTMF in channels, to ensure compliance with
standards, as well as compatibility with older UAs.  

Hope this helps someone.

Sincerely,
David Gomillion