Subject: [AVT] RTCP Inter-Arrival Jitter

From: "Robert Gendron" <[email-masked]>
Date: Mon, 11 Feb 2008 20:15:03 -0500

To whoever could help me,

                       I was looking at the RFC 3550 and in the RTCP RR
messages there is a requirement to report the Inter-Arrival Jitter. It
is not clear to me that the suggested calculations herein are applicable
to Constant Bit Rate (CBR) or Variable Bit Rate (VBR) streams. In the
case of IPTV, depending on the deployment the two types of streams can
be transported. Since the calculations in RFC 3550 resembles the ones
presented in RFC 3393 (IP Packet Delay Variation Metric for IP
Performance Metrics (IPPM)) which are prescribed for CBR (Poisson
distribution) is there any arm is using the RFC 3550 calculation methods
to address these two cases? Could you shed some light on what I might be
missing?

Thanks and Regards,  

Robert.

_______________________________________________
Audio/Video Transport Working Group
[email-masked]
http://www.ietf.org/mailman/listinfo/avt

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From: Randell Jesup <[email-masked]>
Date: Tue, 12 Feb 2008 15:53:14 -0500

>to address these two cases? Could you shed some light on what I might be

From 6.4.1:

      The jitter calculation MUST conform to the formula specified here
      in order to allow profile-independent monitors to make valid
      interpretations of reports coming from different implementations.

The calulations aren't specifically targeted at one or the other, though
you could say that the calculation has an inherent (and hard to avoid)
assumption that packet sizes are the same (or close to); i.e. packet-level
CBR.  (Note that "CBR" often means in practice "constant over time period
X", not "constant bits per packet", especially in video.)

If you want *any* other calculation for jitter, see extended RTCP blocks
(RTCP-XR, RTCP-HR and the like).

-- 
Randell Jesup
[email-masked]
"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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From: "Schwarz Albrecht" <[email-masked]>
Date: Wed, 13 Feb 2008 09:35:08 +0100

RTP packet delay variation (RPDV) is a matter of
a) traffic source (RTP endsystem) and
b) network.

"CBR" and "VBR" are primarily characteristics of the traffic source (a).
The RFC 3550 RPDV calculation algorithm is (and may) not differentiating
between jitter "introduced" by (a) or (b). It's just observing the
traffic arrival process.

The distinction between "CBR" and "VBR" is rather a concept of a
*traffic descriptor*, particular for each (RTP) application.
E.g.,  a "burst size" parameter is e.g. a property to describe (a), i.e.
differences between "CBR" and "VBR". Or a "delay variation tolerance"
parameter could be a measure for expected jitter introduced by (b).

Consequently, the measured and reported jitter by the RTP layer may be
interpreted correctly by the RTP served user instance (when having some
knowledge about traffic descriptor parameters).

-Albrecht

> -----Original Message-----
> From: [email-masked] [mailto:[email-masked]] On Behalf Of
> Randell Jesup
> Sent: Dienstag, 12. Februar 2008 21:53
> To: Robert Gendron
> Cc: [email-masked]
> Subject: Re: [AVT] RTCP Inter-Arrival Jitter
> 
> "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."