Subject: RE: AW: [AVT] Layered codecs: use of PT to distinguish layers

From: "BABONNEAU Gerard RD-MAPS-REN" <[email-masked]>
Date: Tue, 4 Apr 2006 11:00:14 +0200

Hello

I aim to use both coarse and medium granularites
- coarse granularity goes with Ip addresses
- medium granulariry goes with some more precises adjustements, as
bandwidth, by mean of selecting scalable items (NALU) merged in a unique IP
address.

Scalable levels must be distributed properly among Ip addresses according to
the dependancy properties.

For medium granularities, two solutions are possible, in my undertsanding:
- streams in separate ports that allow extra diffserv QoS. But may be some
new problems to resolve for SDP? (to declare multiple sessions with multiple
ports in an IP address)
- streams distinguished by PT is a good challenge with a better
compatibility with other existing protocols (one RTP session for one IP
address), but usage may be less obvious.

Receving all PT for an IP address has no sense if the receiver cannot
receive them (i.e. congestion of data link). In reference to DiffServ, the
only alternative is to insert an RTP translator before the congestion point,
unless routers can analyse RTP headers.

May be it is difficult to imagine accurately today what applications will
benefit from svc streams, and how they will manage them.

>From a transport point of view, I have no preference today, because each
solution for medium granularity has advantages and inconveniences. 

>From an svc stream point of view, the relation between the NALU header and
marking RTP (PT field) or IP packets (DSCP field) needs a carefull look to
be sure that translators, MANE or others treatments in the network must
assure they preserve the best quality of MPEG4-svc streams according to the
reduced rate. I suppose that marking can change according to network
characteristics. 

Regards,

Gérard BABONNEAU 
CRD "Middleware and Advanced PlatformS" (MAPS)
Laboratoire "Distribution et Protection des Contenus" (DPC) </> 

france telecom R&D 
4, rue du Clos Courtel - BP 59 - 35512 Cesson Sevigné Cedex 
Tel : +33 2 99 12 40 08  -  Fax : +33 2 99 12 40 98 
e-mail : [email-masked] 

> Von: Stephan Wenger [mailto:[email-masked]]
> Gesendet: Montag, 03. April 2006 09:55
> An: [email-masked]
> Cc: Magnus Westerlund; Colin Perkins
> Betreff: [AVT] Layered codecs: use of PT to distinguish layers
>
> Folks,
> I want to feel the temperature with you about the use of the RTP 
> payload type field to distinguish layers of a layered codec.  That is, 
> in the same RTP session (IP/Port/SSRC), several layers would be sent 
> as independent RTP streams, distinguished by the PT.  The main 
> rationale is minimization of firewall pinholes.  The advantage of this 
> solution, over putting the layer id into the payload header, is that 
> the RTP header is not encrypted when using SRTP, which allows 
> meaningful layer discarding by middleboxes.
> It is understood that this verges on the border of "RTP payload 
> multiplexing", which is not p.c. in AVT; however, I got encouraged by 
> Colin's recent draft in DCCP, which proposes something similar for RTP 
> and corresponding RTCP traffic.  So let me boldly enter this minefield 
> again.
> I would appreciate quick comments (over the next two days or so), as 
> an endorsement of the idea by this WG could perhaps influence the 
> design choices being made here in the committee which is standardizing 
> the SVC layered video codec.  Thanks very much for your reaction.
> Regards,
> Stephan
>
>
>
> _______________________________________________
> Audio/Video Transport Working Group
> [email-masked]
> https://www1.ietf.org/mailman/listinfo/avt

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Audio/Video Transport Working Group
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Audio/Video Transport Working Group
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