[sip-comm-dev] SDP dynamic media formats not negotiated?


#1

Hi,

I stared at the source code of SIP Communicator now for some time, I'm looking at the negotiation code in CallSessionImpl::createMediaDescriptions(). I have the feeling that I missed something :slight_smile:

- Did I understand it correctly that only static media formats are supported, not dynamic ones, which would have to be specified via rtpmap attributes?

But, a number of payload types as defined in MediaControl::SupportedAudioEncodings fall into the dynamic range (RFC1890), notably 97 (dubbed "ILBC" in a comment) and 110. For these, SIP communicator does not generate a=rtpmap attributes.

- If it were implemented that way for the purpose of supporting them in outgoing calls only, a rtpmap attribute would be neccessary. So why have them at all?
- Are clashes avoided at all, when a client offers a media format in the dynamic range, but with a different codec?

Regards,
Wolfram

路路路

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#2

Hey Wolfram,

I am sorry for the late reply. I guess you've figured that out but still
it is probably worth replying: no we do not handle dynamic media formats
and, as you have noticed yourself, we have hardcoded ilbc to be 97 as a
temporary solution. Interested in contributing a fix?

Cheers
Emil

Wolfram Schroeder 薪邪锌懈褋邪:

路路路

Hi,

I stared at the source code of SIP Communicator now for some time, I'm
looking at the negotiation code in
CallSessionImpl::createMediaDescriptions(). I have the feeling that I
missed something :slight_smile:

- Did I understand it correctly that only static media formats are
supported, not dynamic ones, which would have to be specified via rtpmap
attributes?

But, a number of payload types as defined in
MediaControl::SupportedAudioEncodings fall into the dynamic range
(RFC1890), notably 97 (dubbed "ILBC" in a comment) and 110. For these,
SIP communicator does not generate a=rtpmap attributes.

- If it were implemented that way for the purpose of supporting them in
outgoing calls only, a rtpmap attribute would be neccessary. So why have
them at all?
- Are clashes avoided at all, when a client offers a media format in the
dynamic range, but with a different codec?

Regards,
Wolfram

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