[sip-comm-dev] Dynamic payload for DTMF (or more)

Emil Ivov emcho at sip-communicator.org
Thu Jul 30 17:35:55 CEST 2009


Hey Romain,

Afraid there's no clean way of handling this for now until we have our
new media implementation, which would be moving SDP outside of the media
package. This is being currently handled as part of issue #701

https://sip-communicator.dev.java.net/issues/show_bug.cgi?id=701

Until that's ready we better limit the changes to as few locations as
possible. I don't think you need to be bothering with MediaControl at
all. Just manually add the mapping to audio media descriptions in
CallSessionImpl.

Does this make sense?

Emil

Romain wrote:
> Hi everybody,
> 
> For my DTMF implementation I need to negociate a dynamic payload with
> the remote side.
> 
> I need this behaviour for DTMF, but this same things could happen in
> other Sip Communicator projects :
> https://sip-communicator.dev.java.net/servlets/ReadMsg?listName=dev&msgNo=2553
> <https://sip-communicator.dev.java.net/servlets/ReadMsg?listName=dev&msgNo=2553>
> 
> What is a dynamic payload type?
> In an SDP offer (or answer) there is a media description :
> (m): audio 5000 RTP/AVP 0 8 97 ..... 101
> The last numbers ( 0 8 97 ..... 101 ) correspond to the payload type of
> accepted codec.
> If the number is included in the range 97-127, the payload type is
> dynamic, we don't know the codec name matching this payload type.
> So we add the link in SDP like this :
> (a): rtpmap 101 telephone-event/8000 (this is for DTMF)
> Now the remote side know that the dynamic payload type 101 is for
> telephone-event/8000
> 
> Join in this mail you will find my very dirty hack.
> I negociate the DTMF payload type in CallSessionImpl and MediaControl.
> 
> In CallSessionImpl#createMediaDescriptions() :
> If we receive an SDP offer we  save the Payload Type
> Number. This number will be used in DTMF packets.
> 
> In MediaControl#getSupportedAudioEncodings()
> We add support for the DTMF Payload Type Number.
> 
> In DtmfConstants.DtmfSDP
> The DtmfSDP is not a constant anymore because the remote side can change it.
> 
> 
> When I tried to add DTMF encoding directly in EncodingConfiguration, it
> didn't add DTMF in SDP, but added it in the Codec GUI.
> 
> If you have any ideas how to generalize this
> 
> Cheers
> 
> Romain
> 
> 
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-- 
Emil Ivov, Ph.D.                               67000 Strasbourg,
Project Lead                                   France
SIP Communicator
emcho at sip-communicator.org                     PHONE: +33.1.77.62.43.30
http://sip-communicator.org                    FAX:   +33.1.77.62.47.31

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