[asterisk-dev] DTMF offer oddities

Marcus Hunger hunger at sipgate.de
Tue Apr 10 05:00:45 MST 2007

huh? schon irgendwas festgestellt?

On Wednesday 21 March 2007 10:17, Sebastian Damm wrote:
> Hi,
> I've noticed some changes in handling of DTMF offers in SIP packages
> since my last update of Asterisk to 1.2.16.
> The behavior was somehow "foreseeable" still at version 1.2.13, at 1.2.15
> it was already "different". Don't know about 1.2.14.
> Here is how it should be (according to my knowledge):
> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> Clients are only allowed to send INFO packets, if INFO is listed in the
> Allow line (if present). Otherwise the client must not send INFO packets
> at all.
> RfC2833:
> Clients shall only send RfC2833 RTP event packages, if there are lines
> like the following in the SDP part of the INVITE/183/200 OK:
> 	a=rtpmap:101 telephone-event/8000
> 	a=fmtp:101 0-16
> If those lines are missing, the devices indicates that it cannot process
> RTP event packages.
> inband:
> Inband DTMF tones can be sent always, as they are transmitted within the
> audio stream.
> Now what Asterisk is doing. You have two ways of defining the DTMF mode.
> One is in sip.conf and one is in the dialplan with the DTMFMode command.
> If you have set dtmfmode=rfc2833 in sip.conf:
> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> When replying to incoming INVITEs, which don't have those rtpmap lines
> mentioned above, Asterisk doesn't offer rtpevents. Why? If I want some
> kind of autodetection, I set dtmfmode to auto in sip.conf.
> When replying to incoming INVITEs with rtpevents offered, Asterisk
> includes rtpevents, too. So that behavior is fine.
> When setting the dtmfmode dynamically to info via dialplan, asterisk does
> not offer rtpevents. That should be correct, too. But Asterisk does not
> append the INFO method to the Allow line.
> If you have set dtmfmode=info in sip.conf:
> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> Asterisk does never append the INFO method to the Allow line. This
> behavior has always been like this. Devices checking on the Allow line
> will never send INFO packets to an Asterisk server.
> When setting the dtmfmode to rfc2833 dynamically via dialplan, Asterisk
> does not offer rtpevents in it's answers. Clients checking on this send
> DTMF tones inband because neither the allow line nor the rtpevents line
> indicate one of the "better" method being supported.
> In Asterisk 1.2.13 at least the rtpevents were always offered, no matter
> what the dtmfmode setting said. While that was also not correct, it
> allowed most clients to communicate at least via rfc2833 with our
> servers.
> Background: We have the peers in our network set to dtmfmode=info as
> standard, then we set the dtmfmode to rfc or inband if required in a
> conversation. This does not work anymore for some clients since the
> update to 1.2.16, because some clients which sent rfc2833 dtmf tones
> before now send their dtmf tones inband.
> From my point of view the behavior of dtmf offers is buggy. Can we do
> something about it?
> Best regards,
> Sebastian
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Marcus Hunger - hunger at sipgate.de
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