Re: [AVT] draft-schierl-avt-rtp-multi-session-transmission-00.txt

[<Ye-Kui.Wang at nokia.com>]

I tend to agree with Ingemar that the problem of the RTP header extension mechanism is not serious. If the RTP header extension mechanism is based on decoder order numbers of coded data units, then I think it is really generic and applies to any layered or multi-source codec, including flexible scalable video codecs such as SVC.

BR, YK 

>-----Original Message-----
>From: avt-bounces at ietf.org [mailto:avt-bounces at ietf.org] On 
>Behalf Of ext Ingemar Johansson S
>Sent: 13 November, 2008 17:27
>To: avt at ietf.org
>Subject: Re: [AVT] 
>draft-schierl-avt-rtp-multi-session-transmission-00.txt
>
>Hi
>
>I have a comment on 
>draft-schierl-avt-rtp-multi-session-transmission-00.txt
>
>
>=============
>7.2.6.  RTP header extension
>
>   The RTP header extension may be used to add generic signaling about
>   Data Alignment to RTP packets.
>
>7.2.6.1.  Identified problems
>
>   RTP header extensions are required to be ancillary information which
>   can safely be discarded by receivers which do not understand them.
>   Data alignment mechanisms do not satisfy this requirement.
>=============
>
>My question is ..how serious is the identified problem ?. 
>My gut feeling is that a receiver that implements e.g decoding 
>of G.718 content will likely update the RTP stack to recognize 
>header extensions if header extensions are used to carry e.g 
>the NTP timestamp related to the RTP timetstamp in the RTP header. 
>I see many benefits with using the RTP header extension for 
>this purpose: 
>1) It is relatively compact 
>2) Easy to make generic (I would believe that the NTP is all 
>info that is needed)
>3) The clock-skew issue is easily solved as you don't need to 
>schedule the transmission of the header extension like for 
>RTCP-SR. For instance for a layered audio codec you typically 
>add the header extension for all layers corresponding to the 
>same exact time instant.
>
>Regards
>Ingemar
>******************************************* 
>Ingemar Johansson 
>Senior Research Engineer, IETF "nethead" 
>EAB/TVP - Multimedia Technologies 
>Ericsson Research Ericsson AB 
>Box 920 S-971 28 Luleå, Sweden 
>Tel: +46 (0)8 4043042 
>ECN: 850-43042 
>Mobile: +46 (0)730 783289 
>******************************************* 
>_______________________________________________
>Audio/Video Transport Working Group
>avt at ietf.org
>https://www.ietf.org/mailman/listinfo/avt
>
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