[SIP] draft-camarillo-sip-sdp-00.txt

Hi,

I'm not writing to present a problem with this proposal but to state a need
for it?

For a specific case not mentioned in the draft.  A "3rd-party call agent"
may need to be able to receive tones and also have them be presented to the
2nd party.  Tone transport is defined by RFC2833, it recommends that
gateways remove the tones from the audio media.

So..., I'd like an endpoint to understand the following media description in
a session description.

m=audio 10010 RTP/AVP 4
c=IN IP4 111.2.30.4
a=rtpmap:4 G723/8000
m=audio 10020 RTP/AVP 97
c=IN IP4 111.2.30.4
a=rtpmap:97 telephone-event
a=fmtp:97 0-15
m=audio 20000 RTP/AVP 97
c=IN IP4 111.2.31.10
a=rtpmap:97 telephone-event
a=fmtp:97 0-15,16

(In this case one "c" line can be used in the session description instead of
how it's shown.)

Nothing I read in RFC 2543 (SIP) and RFC 2327 (SDP) indicates the above is
not allowed.  This is not a standards issue but I wonder how many endpoints
(gateways included) will support sending the two media types to the
different destinations as indicated above.  If in SIP the above session
description doesn't result in three "media streams" being sent to the
indicated host/port, media replication (which may not be present in an
endpoint) will require a specific resource in the network.

Is the use of the flow ID attribute required to achieve the above?  Am I
incorrect in what I think should result from the above session description
in SIP?

The ID does seem to encourage endpoint support for media replication to
different hosts and ports which I'd like to see as standard functionality in
some endpoints & environments.

Regards,
Bert

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