Subject: [Sipping] Re: Early media: a summary

From: William Marshall <[email-masked]>
Date: Tue, 3 Dec 2002 10:10:36 -0500 (EST)

Gonzalo,

I've read through your updated version 00 of the draft, and still have
a number of major concerns with it.

First and foremost, we had a long discussion last summer on this email
list during the last call on the sip-isup draft, leading to consensus
on handling of early media and in-band-ringback.  I see no reason why
the agreements of last summer need to be scrapped in favor of a complete
new mechanism,  If there is some cruical flaw in the solution contained
in draft-ietf-sipping-isup-06, please describe it.

Second, I believe the only real use of early media, as you have defined it
in section 1, is for interworking with legacy systems, particularly the
PSTN.  Numerous complex issues (which are not addressed in your draft)
of e.g. early-media-on-hold, call-transfer of early media, etc, lead me
to believe the concept should not be encouraged for SIP-SIP connections.
And if the only real use is for interworking with the PSTN, again the
proper place for the definition of how it is done is the sip-isup draft.
(A SIP endpoint that wants to act like the PSTN can follow those rules too).

Media clipping is certainly a real problem, and needs to be addressed.  
But your "early media" definition in Section 1 is "from the moment the 
initial INVITE is sent until the UAS generates a final response".  The
clipping problems occur between the UAS generating the final response and
the UAC processing it.  Your new "a=intention" does nothing to solve
the problem.  And section 6.2 should only be given as a bad example that 
should not be followed, since the additional offer/answer exchange after 
pickup will guarantee clipping.

Your example in section 2.3 sounds like a requirement for the equivalent
of video comfort noise.  The equivalent of silence suppression would also
be nice (i.e. how long to continue sending images of a blank wall?) 
And I continue to believe that end-to-end signaling of the mute button 
is harmful, and should be discouraged.

Bill Marshall
[email-masked]
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From: Gonzalo Camarillo <[email-masked]>
Date: Tue, 03 Dec 2002 17:23:31 +0200

Bill,

inline:

> in draft-ietf-sipping-isup-06, please describe it.

That draft says that the early media solution described is a "simple"
one. We already anticipated at that point in time that a fully-featured
early media solution was in its way.

> proper place for the definition of how it is done is the sip-isup draft.

I do not agree that early media is about PSTN interworking. Take
Jonathan's draft on application server interaction and you will see
several examples of early media.

> pickup will guarantee clipping.

No with the intention attribute.

> be nice (i.e. how long to continue sending images of a blank wall?)

This has to do with video compression, not with a sender stopping
sending video.

> is harmful, and should be discouraged.

Please, re-read the last proposal. You would not touch the media
configuration when the user presses mute. But the intention attribute
would give you a means to inform the other end that you have done so...
anyway, I guess what we have to decide is what I asked in my previous
mail (the one I sent a couple of minutes ago). Do you think it is
worthwhile resolving the first bullet of that mail?

Thanks,

Gonzalo

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From: Christer Holmberg <[email-masked]>
Date: Tue, 03 Dec 2002 17:34:58 +0200

Hi,

One could agree that the only scenario where this will be used is when we are
interworking with PSTN, and that early media should not be used between SIP
phones.

However, I am not sure I agree with the statement that it only belongs in the
ISUP/SIP draft. The reason for that is that this issue doesn't only affect PSTN
gateways - it also affects the normal SIP phones communicating with the PSTN
gateways. I think we want a solution which allows SIP phones, as well as PSTN
gateways, to know and/or indicate if there is early media or not. And, since a
SIP phone may not know if it communicates with a PSTN gateway or another SIP
phone, and a PSTN gateway may not know if it communicates with a SIP phone or
another PSTN gateway, I think we need a generic solution.

And, if we first find a solution, we can then argue about in which document to
put it :)

Regards,

Christer Holmberg
Ericsson Finland