Re: [AVT] Comments on the major open issue of draft-ietf-avt-rtp-svc-07.txt, cross layer decoding order dependency

["Jonathan Lennox" <jonathan at vidyo.com>]

mike.nilsson at bt.com writes:
> The major weakness of the CL-DON method is that it is not backwards
compatible with the single NAL unit mode of RFC 3984.

Another weakness of the CL-DON method is that it does not support NAL
unit fragmentation in mode 1.  RFC 3984 FU-A packets cannot include a
CL-DON, since mixing aggregation and fragmentation isn't allowed.

Though it's better to avoid it if you can, there are scenarios where
fragmentation is needed, i.e. video being transmitted over a network
with an MTU lower than the video encoder expected.  If retransmission or
FEC is in use, RTP-layer fragmentation is hugely preferable to IP-layer
fragmentation of the RTP packet.


More architecturally, I wonder if cross-layer decoding is a question
that should be addressed in a generic manner rather than per-media.
Several drafts have been presented recently for audio codecs which do
session multiplexing in a very similar way to H.264/SVC, and they also
need to be able to indicate a global decoding order.  Should this be
addressed as a generic problem?

-- 
Jonathan Lennox
Vidyo, Inc (formerly Layered Media)
jonathan at vidyo.com

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