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

[Gonzalo Camarillo <[e-mail]>]

Hi,

I have gathered some feedback on the draft
draft-camarillo-sip-sdp-00.txt
The general feeling in the SIP and MMUSIC WGs is that this is certainly
a useful mechanism.

However, there are some concerns about the actual format to be used and
the problems that some RTP implementation might have if an RTP flow is
sent to different port numbers.

A possible solution to the format to be used is already outlined in the
draft in section 7. "Backward compatibility".

I will check what people in the Audio/Video Transport (avt) WG
<[e-mail]> think about this.

Regards,

Gonzalo

"Culpepper, Bert" wrote:
> 
> 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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-- 
Gonzalo Camarillo         Phone :  [phone]
Oy L M Ericsson Ab        Mobile:  [phone]
Telecom R&D               Fax   :  [phone]
FIN-02420 Jorvas          Email :  [e-mail]
Finland                   http://www.hut.fi/~gonzalo

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