Re: [AVTCORE] multi session draft-ejzak-avtcore-rtp-subsessions-00.txt

[Harald Alvestrand <[e-mail]>]

On 06/04/2012 01:07 AM, Ejzak, Richard P (Richard) wrote:
> http://www.ietf.org/id/draft-ejzak-avtcore-rtp-subsessions-00.txt
>
> In response to the chairs' request for additional input on the multi session issue, I have submitted this draft for your consideration.  There are superficial similarities with an expired draft from last year in http://tools.ietf.org/id/draft-rosenberg-rtcweb-rtpmux-00.txt, but my draft has a different take on the use of SSRC as the basis for multi session multiplexing that I think is superior and worthy of consideration as a potential replacement for BUNDLE and/or SHIM.  Please comment.
Since this draft is destined for AVTCORE, I'll repeat my comments from 
the RTCWEB discussion here, and encourage people to keep the discussion 
on AVTCORE:

Richard,
having scanned your draft:

- I still fundamentally think that the partition of media types into 
separate RTP sessions was a design mistake that we should seek to 
rectify, not promulgate, and additional complexity like what you propose 
for perpetuating the use of "separated" sessions is not helpful. See 
draft-alvestrand-rtp-sess-neutral for details.

- When we have parts of the ecosystem that have code that is written on 
the assumption that the SSRC space is a 32-bit flat space, I think the 
partitioning of that space into subspaces as you propose is likely to 
lead to "interesting" bugs. We should reinforce the randomness and 
flatness of the SSRC space, not partition it.

- You say "The biggest problem with BUNDLE is that it is
    difficult to partition the RTP streams associated with different
    media lines since this requires filtering on sets of payload type
    values.  RTP subsessions is superior for this purpose since it is
    only necessary to screen for a single value in the first 16 bits".
This assumes that the partitioning associated with different media lines 
is a good thing.
I claim that it is not.

If there are no bigger problems than that with BUNDLE, I would prefer to 
stick with that approach.

>
> Richard
>
> -----Original Message-----
> From: [e-mail] [mailto:[e-mail]]
> Sent: Sunday, June 03, 2012 5:16 PM
> To: Ejzak, Richard P (Richard)
> Subject: New Version Notification for draft-ejzak-avtcore-rtp-subsessions-00.txt
>
> A new version of I-D, draft-ejzak-avtcore-rtp-subsessions-00.txt has been successfully submitted by Richard Ejzak and posted to the IETF repository.
>
> Filename:	 draft-ejzak-avtcore-rtp-subsessions
> Revision:	 00
> Title:		 Media multiplexing with Real-time Transport Protocol (RTP) subsessions
> Creation date:	 2012-06-04
> WG ID:		 Individual Submission
> Number of pages: 9
>
> Abstract:
>     This document describes a means of multiplexing RTP streams having
>     different media types within a single transport connection and how to
>     represent this multiplexing option in SDP.  This mechanism is an
>     alternative to the BUNDLE and SHIM proposals currently under active
>     consideration in AVTCORE.  Instead of adding an extra multiplexing
>     header as in SHIM to allow multiple RTP sessions within a single
>     transport connection, or using the payload type field to separate
>     different media streams within a single RTP session, this document
>     describes how to partition the existing SSRC space to create RTP
>     subsessions from a single RTP session.  A filter can be used to
>     identify each RTP subsession for different QoS handling as necessary.
>     RTP subsessions can be treated like RTP sessions with a few
>     restrictions.  In particular, SSRC mapping may be needed when
>     forwarding RTP streams into an RTP subsession to avoid SSRC
>     conflicts, but there are few use cases in which this limitation is a
>     concern and RTP subsessions can be disabled if necessary.
>
>
>
>
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