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

[Colin Perkins <csp at csperkins.org>]

Err, no. Things like decoding order number go into an RTP payload  
header, as part of a payload format, not into a header extension.

Colin


On 16 Nov 2008, at 16:46, <Ye-Kui.Wang at nokia.com> wrote:
> Thanks for the clarification, which is important. According to  
> this, it
> appears that if the RTP header extenstion contains Decoder Order  
> Number
> information, then there is no problem, as this information not related
> to anything in the RTP header. A good thing is that this solution is
> really generic!
>
> BR, YK
>
> > -----Original Message-----
> > From: ext Randell Jesup [mailto:rjesup at wgate.com]
> > Sent: 16 November, 2008 17:19
> > To: Wang Ye-Kui (Nokia-NRC/Tampere)
> > Cc: ingemar.s.johansson at ericsson.com; avt at ietf.org
> > Subject: Re: [AVT]
> > draft-schierl-avt-rtp-multi-session-transmission-00.txt
> >
> > <Ye-Kui.Wang at nokia.com> writes:
> > > > > > 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.
> > > >
> > > > What if an intermediary deletes the header extension?  (SBC, B2BUA,
> > > > raw message store, etc).
> > >
> > > What are the (good) reasons for an intermediary to delete header
> > > extensions? Isn't so that if there is something an
> > intermediary does not
> > > understand, it'd better not to touch the something?
> >
> > True - but if you modify the main package, passing through the header
> > extension becomes tricky.  For example, a B2BUA may leave the payload
> > alone, but almost always rewrites the RTP header, and may
> > generate it's own
> > (or modify passed-through) RTCP packets.  If the header extension
> > references the header (sequence or timestamps), you could be
> > broken.  Or if
> > the header extension references the SSRC, or data carried in the RTCP
> > stream (like NTP time), you could also be broken, and there's no  
> > way to
> > know if you don't understand (and comply with) the extension.
> >
> > I mention things like this because Asterisk does those
> > actions, I 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)
> _______________________________________________
> Audio/Video Transport Working Group
> avt at ietf.org
> https://www.ietf.org/mailman/listinfo/avt



--
Colin Perkins
http://csperkins.org/



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