RE: [AVT] jitter+seqno generation 3550

["Even, Roni" <[e-mail]>]

Hi,
First of all RTP +RTCP compose the RTP so if you do not use (send) RTCP  I would not call the implementation RTP compliant. Now if you chose to ignore the received RTCP stream and send only the minimal RTCP information this is OK if you do not have any use for it. Still the other side may want you sender/receiver reports to monitor the RTP session.

Seq no are important to verify that the delivery order is correct.

As for usage of the timing information, this is important in order to synchronize between streams like lip synch for audio and video or for sending multiple layers in a layered codecs using separate RTP sessions.

Other usage of RTCP adding to Bob's are using the RTCP feedback profile for end to end media controls and indications

Roni Even

> -----Original Message-----
> From: Greg Herlein [mailto:[e-mail]]
> Sent: Friday, January 11, 2008 7:17 PM
> To: Bob Gilman
> Cc: [e-mail]
> Subject: Re: [AVT] jitter+seqno generation 3550
> 
> I've heard that some use SN and TS for clock syncronization, but to be
> honest, I've never seen it in the wild.  In the applications I have
> seen, the clock sync is not something that really matters all that
> much at the RTP layer.  It's something that matters greatly at the
> MPEG payload processing layer or at the voice codec processing layer -
> but both are lower layers that the RTP code is not able to really
> affect.
> 
> Of course, this is in the hardware and software stacks that I have
> experience with.  I'd love to learn more about applications where
> clock sync is actually performed with RTP layer information.
> 
> Greg
> 
> On 1/11/08, Bob Gilman <[e-mail]> wrote:
> >
> >  Knowledge of received sequence numbers is critical for packet loss
> > concealment algorithms.
> >  It's useful, along with the timestamp, for clock synchronization with
> the
> > received stream.
> >  The sequence number is also used, along with the rollover counter, by
> SRTP
> > to provide a unique
> >  keystream for each packet and to prevent replay attacks.
> >  -Bob
> > -------------------------------------------------------------
> > Bob Gilman [e-mail] 303 898 9780
> >
> > Greg Herlein wrote:
> > Well, at a minimum it's useful to detect (and correct) out of order
> > packets. But, I suppose there's nothing to say you cannot just ignore
> > it.
> >
> > Why do so few implementations support RTCP? It's one of my pet
> > peeves. RTCP is well worth adding. Why not add it?
> >
> > Greg
> >
> > On 1/11/08, Lakshmi Thampi <[e-mail]> wrote:
> >
> > Hello
> >  In reference to RFC 3550, Appendix A.1
> >
> > If the RTCP functionality is not used then can we assume that sequence
> no is
> > not a valid in RTP header
> >
> > regards
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