Subject: RE: [Megaco] Multi Media SDP

From: "Tom-PT Taylor" <[email-masked]>
Date: Thu, 6 Sep 2001 19:20:54 -0400

Agreed.

-----Original Message-----
From: Troy Cauble [mailto:[email-masked]]
Sent: Thursday, September 06, 2001 6:28 PM
To: MEGACO list
Subject: [Megaco] Multi Media SDP

SDP (RFC 2327) supports multimedia sessions, that is 
Sessions containing multiple Media.  

For example, the SDP below specifies 1 Session with 
audio and video Media streams with different remote 
addresses and using different coders.

         v=0
         m=audio 3456 RTP/AVP 0
         c=IN IP4 128.96.41.1
	 a=sendrecv
         m=video 7890 MyVideoSpec 2 18
         c=IN IP4 128.96.41.2
	 a=sendrecv

Note that when the "c=" line is below an "m=" line,
it refers to that Media stream only.

I would like to see an IG clarification that within H.248, 
SDP Session descriptions MUST NOT contain multiple Media 
descriptions, since an H.248 Stream Descriptor represents 
a single media stream.

-troy

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From: Christer Holmberg <[email-masked]>
Date: Fri, 07 Sep 2001 07:40:07 +0300

Hi,

What did you mean by "multiple session descriptions" for a single
stream? Did you mean multiple Local/Remote descriptors, multiple m=
lines, or specific c= lines for every m= line?

By using the ReserveXxx values, isn't it possible give provide multiple
m= lines (with or without specific c= lines for each) and ask the MG to
reserve resources for ONE of those? If the MG is asked to reserve
resources for ALL of them, for a single strem, I guess we may an issue,
though...

In your example you also have different type of media (audio and video)
in your m= lines, so I guess that is another issue if it should be
allowed or not for a single stream. But, I see no reason why we should
not allow multiple m=audio lines (or m=whatever...) if we then ask the
MG to choose one of those.

I am sorry if I missunderstood the question, and what I just wrote had
nothing to do with your issue :)

Regards,

Christer Holmberg
Ericsson Finland

---

From: Christer Holmberg <[email-masked]>
Date: Fri, 07 Sep 2001 07:44:21 +0300

Hi again,

I guess I missunderstood the question, after all :)

I didn't notice that there wasn't any v=0 line between the session
descriptions in the example, so I guess what you wrote is not allowed -
whatever the ReserveXxx values are.

Regards,

Christer Holmberg
Ericsson Finland

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From: Terry L Anderson <[email-masked]>
Date: Fri, 07 Sep 2001 16:35:02 -0400

Troy-
would this capture your concern.

7.1.8 Local and Remote Descriptors
(add two sentences to the beginning of the paragraph below the first set
of bullets)

A Stream Descriptor specifies a single bi-directional media stream and
so a single session description MUST NOT include more than one media
description ("m=" line).  Any additional media streams for a termination
must appear in distinct Stream Descriptors.  When multiple session
descriptions...

--

------------------------------------------------------------
Terry L Anderson              mailto:[email-masked]
Tel:908.582.7013   Fax:908.582.6729
Lucent Technologies/INS/Voice Over IP Access Networks
Rm 2B-121, 600 Mountain Av, Murray Hill, NJ 07974
http://its.lucent.com/~tla (Lucent internal) http://www.gti.net/tla

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From: Troy Cauble <[email-masked]>
Date: Fri, 07 Sep 2001 18:03:42 -0400

Terry,

It captures my concern, but is SDP centric.

I'd prefer to see the SDP portions of your two sentences below 
AND the other SDP specific stuff in 7.1.8 moved to Annex B.

(see below)

Terry L Anderson wrote:
> A Stream Descriptor specifies a single bi-directional media stream 

This is generic enough for 7.1.8.

> and
> so 

> a single session description MUST NOT include more than one media
> must appear in distinct Stream Descriptors.  

This should go in Annex B.

-troy

> When multiple session

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From: Terry L Anderson <[email-masked]>
Date: Fri, 07 Sep 2001 18:14:46 -0400

> AND the other SDP specific stuff in 7.1.8 moved to Annex B.

I am just adding to a paragraph that is nearly all SDP specific.  Perhaps it
should have been in Annex B but I don't want to do that much reorganization
through IG.  V2 might do that.  I believe that the addition is in similar
spirit to what is currently there and its the main place the use of SDP for
text-encoding is discussed.  So I think that for V1 the addition should go
there.

> This is generic enough for 7.1.8.

By itself it simply duplicates the first sentence of 7.1.6 (where I got it
from).  It is only useful as a leadin to the rest.

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