Subject: draft-kutscher-mmusic-sdpng-req-01.txt

From: Dirk Kutscher <[email-masked]>
Date: 29 Nov 2000 12:28:39 +0100

Folks,

we have submitted a new version of the SDP-ng requirements
draft. Until it appears in the archives you can get it also at

http://www.dmn.tzi.org/ietf/mmusic/49/id/draft-kutscher-mmusic-sdpng-req-01.txt

PS- and HTML-versions are also available.

We have adopted the results of our requirements discussion at the last
IETF meeting and also provided a strawman proposal as input for
further discussions.

Any comments etc. are welcome.

-- 
	Dirk

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From: Thomas LEVY <[email-masked]>
Date: Tue, 05 Dec 2000 16:45:03 +0100

Hello Dirk,

Concerning the "requirements for capability description and negotiation", it seems
to me that your document mainly focus on end systems.
To be more precise, the main discussed problem in part 5. (you call it "negotiation
of capabilities") is to ensure that a stream getting out of a system A is
compatible with a stream getting in a system B. We only see a system as an "opaque
box" being able to initiate or to terminate streams.

But what about considering that the system may "transform" one (or more) input
streams into one (or more) output streams?
Considering this, an end system could be considered as terminating an input stream.
A transcoding media gateway system could be considered as transforming an input
stream with codec of a certain type into an output stream with a codec of an other
type...
It could allow to enlarge the scope covered by capability description.

Thomas,

---

From: Dirk Kutscher <[email-masked]>
Date: 09 Dec 2000 04:48:07 +0100

>>>>> "Thomas" == Thomas LEVY <[email-masked]> writes:

    Thomas> Concerning the "requirements for capability description
    Thomas> and negotiation", it seems to me that your document mainly
    Thomas> focus on end systems.  To be more precise, the main
    Thomas> discussed problem in part 5. (you call it "negotiation of
    Thomas> capabilities") is to ensure that a stream getting out of a
    Thomas> system A is compatible with a stream getting in a system
    Thomas> B. We only see a system as an "opaque box" being able to
    Thomas> initiate or to terminate streams.

    Thomas> But what about considering that the system may "transform"
    Thomas> one (or more) input streams into one (or more) output
    Thomas> streams?  Considering this, an end system could be
    Thomas> considered as terminating an input stream.  A transcoding
    Thomas> media gateway system could be considered as transforming
    Thomas> an input stream with codec of a certain type into an
    Thomas> output stream with a codec of an other type...  It could
    Thomas> allow to enlarge the scope covered by capability
    Thomas> description.

Thomas,

actually we have also had the transcoding gateway model in mind,
although we have not mentioned it explicitely. Thanks for bringing
this up, we will add a corresponding paragrpah.

Do you see any parts in the listed requirements ore the sketched model
that are in conflict with requirements for the gateway scenario?

-- 
	Dirk

---

From: Thomas LEVY <[email-masked]>
Date: Wed, 20 Dec 2000 15:51:19 +0100

Dirk,

Please apologize for my sarcastic comment during Mmusic meeting concerning
Media Gateway capabilities, I wasn't aware about  your message.
Concerning SDP-ng:
I agree with you that nothing in your document is conflicting with the
idea of capabilities for media gateway.
But section "5.1 Capability Constraints", is not clear to me.
You define capability negotiation in the following way:
"Capability negotiation is used to gain a session description (an actual
configuration) that is compatible with the different end system
capabilities and user preferences of the potential participants of a
conference."

I am not sure to understand what you mean by "end system"  (Perhaps, it is
just a question of terminology).
In my mind, a media gateway acting as a transcoder is not a "end system".
I imagine a case, where 2 VoIP terminals (T1 and T2) have incompatible
codecs transcoded by a Media Gateway MG1 controlled by a Media Gateway
Controller MGC1. In this case, I would say that there are 2 sessions to
negociate (one with negotiation between T1, MG1 and MGC1 and one between
T2, MG1 and MGC1).

Thomas,