Subject: [AVT] draft-clark-avt-rtcpxr-video-02

From: "Hedayat, Kaynam" <[email-masked]>
Date: Tue, 11 Jul 2006 23:48:46 -0400

I have concerns with the packet loss metrics reported in the proposed blocks (RTP and MPEG TS). The Burst and Gap models are based on the VoIP metrics block of RTCP-XR that were used for consistency with other standards for voice quality algorithms. I suggest either replacing burst and gap with packet loss period and packet loss distance based on RFC3357 or augmenting them with these metrics. RFC3357 metrics are better defined and more accurately represent packet loss behavior.

Regards,
Kaynam

-----------------------------------------
Kaynam Hedayat
Chief Technology Officer
Vice President, Engineering

Brix Networks
285 Mill Road
Chelmsford, MA 01824
tel. 978.367.5611
fax. 978.367.5700
[email-masked]
www.brixnet.com

Service Quality Matters. Test the performance and quality of your VoIP or IP video service at http://www.TestYourVoIP.com  <http://www.testyourvoip.com/>  and http://www.TestYourIPVideo.com <http://www.testyouripvideo.com/>  

_______________________________________________
Audio/Video Transport Working Group
[email-masked]
https://www1.ietf.org/mailman/listinfo/avt

---

From: Alan Clark <[email-masked]>
Date: Wed, 12 Jul 2006 14:28:55 -0400

Kaynam
 
You are quite incorrect.
 
(i) The burst and gap metrics were originally defined in RFC3611 (RTCP XR)
and, as they are extremely helpful in understanding the impact of IP
impairments on VoIP, were then adopted in eight other standards related to
VoIP performance.    Hence the original work was done in AVT and then
adopted across the industry
 
(ii) The concepts used in RFC3611 are quite different to those in RFC3357
for good reason.  We analyzed the distribution of lost packets on many
traces and found that "burstiness" tended to be exhibited as periods of high
loss and NOT as periods of consecutive loss. We also found that periods of
high PDV typically coincide with periods of high loss, and hence see merit
in measuring the impact of loss and PDV together (i.e. loss/discard
distribution).
 - The loss period you refer to from RFC3357 defines only consecutive loss
and not the sparse bursts that typically occur (particularly at the network
edge), whereas RFC3611 describes sparse bursts
 - RFC3357 only applies to lost packets, and not to packets discarded due to
late arrival, whereas the model from RFC3611 applies to the combined
loss/discard distribution
 
A good summary of the rationale behind the burst/gap model is
http://www.telchemy.com/reference/ITUSG12_PacketLossDistribution.pdf

I totally disagree with your assertion that RFC3357 metrics are better
defined and more accurately represent packet loss behavior - you are
entitled to hold any opinion you like however if you want to express an
opinion should explain the justification for it.  Any of these measurements
essentially comprise parameters of some assumed model that describes the
behavior of the system being measured.  You should try and ensure that the
model is relevant with regard to the aspect of the system behavior you are
interested in.  You could argue that the assumed model is or is not a good
fit for the aspect of system behavior that is of interest, or that the
method for parameter estimation is more or less accurate.
 
Alan

  _____  

From: Hedayat, Kaynam [mailto:[email-masked]] 
Sent: Tuesday, July 11, 2006 11:49 PM
To: [email-masked]
Subject: [AVT] draft-clark-avt-rtcpxr-video-02

I have concerns with the packet loss metrics reported in the proposed blocks
(RTP and MPEG TS). The Burst and Gap models are based on the VoIP metrics
block of RTCP-XR that were used for consistency with other standards for
voice quality algorithms. I suggest either replacing burst and gap with
packet loss period and packet loss distance based on RFC3357 or augmenting
them with these metrics. RFC3357 metrics are better defined and more
accurately represent packet loss behavior.

Regards, 
Kaynam 

Brix Networks 
285 Mill Road 
Chelmsford, MA 01824 
tel. 978.367.5611 
fax. 978.367.5700 
[email-masked] 
 <http://www.brixnet.com> www.brixnet.com 

Service Quality Matters. Test the performance and quality of your VoIP or IP
video service at  <http://www.testyourvoip.com/> http://www.TestYourVoIP.com
and  <http://www.testyouripvideo.com/> http://www.TestYourIPVideo.com