Re: [AVT] draft-ietf-avt-rtp-svc-03.txt and RFC 3984 (sprop-parameter-sets)

[Randell Jesup <rjesup at wgate.com>]

"Even, Roni" <roni.even at polycom.co.il> writes:
>I understand why most H.264 video conferencing will not use
>sprop-parameter-sets. I think this was not a good idea. Synchronizing
>between signaling and media is not there.

So how then do you guarantee the parameter set is available?  (And that
it's the 'right' one)?  In-stream use, though common, mostly works when
there's only a single set and they never, ever change.  It also wastes
bandwidth.

If you're changing/adding parameter sets in-stream, you're betting on luck
that they get through, and probably sending them on every IDR (and perhaps
either forcing extra IDRs or extra SPS/PPS's into the stream, in case they
got lost).  

Or you have to come up with a separate reliable transport over RTP and
RTCP, or re-use/mis-use some other SIP command to change them (INFO).

>Using re-invite for changing sets or as a response for FIR is not the
>best solution.

Who would use re-INVITE as a response to FIR?  Either they're in-stream (in
opposition to the RFC, though harmless if they're the same as the
sprop-parameter-set value), in which case you can repeat them in response
to an FIR, or they were in signalling to start with, in which case you
don't need to re-INVITE to send them.

>We moved all media control requests (fast update) to the
>media path and now you have to send the parameter sets in the signaling
>path so what was gained, we lost more since INFO has less overhead on
>the SIP UA then the re-Invite

Parameter sets need a reliable transport, unlike fast-update.  Fast-update
has nothing to do with parameter sets.  And are you saying we should send
parameter updates via INFO?  We could do that, and it can be reliable and
lower-overhead than re-INVITE, but I've never seen a spec for it, and also
how often do you expect to change parameter sets?  It also could complicate
things like B2BUA's, I'd think.

-- 
Randell Jesup, Worldgate (developers of the Ojo videophone), ex-Amiga OS team
rjesup at wgate.com
"The fetters imposed on liberty at home have ever been forged out of the weapons
provided for defence against real, pretended, or imaginary dangers from abroad."
		- James Madison, 4th US president (1751-1836)


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