Subject: [ippm] evaluating "loss constraint" for multimedia codecs

From: Haim Zlotokrilov <[email-masked]>
Date: Thu, 11 Apr 2002 11:35:23 +0200

Hi
In "One-way Loss Pattern Sample Metrics" draft, the
'Type-P-One-Way-Loss-Noticeable-Rate' is suggested and based upon the "loss
constraint".
It seems like a useful metrics to evaluate perceive quality for multimedia
codecs. 
Does anybody know what is a typical (or at least the range) "loss
constraint" for voice or video codecs? Is it in the range of 1-10/10-100 or
more?
Do you know of any researches that might be helpful in answering this
question?

Best Regards

---

From: "Alan Clark" <[email-masked]>
Date: Fri, 12 Apr 2002 20:02:47 -0400

evaluating "loss constraint" for multimedia codecsWe have conducted
extensive research on the impact of packet loss and packet loss distribution
on voice codecs, and have characterized all the ITU G.7xx codecs plus a fair
number of proprietary ones.

If packet loss concealment is used, which is quite typical, then packet loss
rates of (say) 3% or more are "noticeable" however I don't think that you
could make that observation based on a single pair of lost packets.  In some
cases error mitigation methods are able to deal with higher rates and hence
the mapping of loss rate to subjective impact needs to be codec dependant.

I also hold the opinion that packet loss is often "not" the problem - with
emerging enterprise VoIP and IP centrex services it is quite likely that
degradation would be caused by congestion on access links leading to jitter
and delay variations and hence packet discards by the receiving jitter
buffer.  This is difficult to figure out from RTCP reported jitter (assuming
the end system generates RTCP) as jitter buffers are dynamic in nature,
hence this needs to be estimated by analysing the variation in RTP arrival
time.

Our approach is to model burst packet loss AND discard distribution using a
Markov Model and to determine the mean burst density and burst length - this
can be done easily in real time during a VoIP call and can be loss-event
driven to conserve processing power - if the burst density is more than 3%
then we regard that as a noticeable event and determine the effect that it
would have on the listener, given the length and density of the burst and
the codec being used.

Regards

Alan Clark
Telchemy

  -----Original Message-----
  From: [email-masked] [mailto:[email-masked]]On Behalf Of
Haim Zlotokrilov
  Sent: Thursday, April 11, 2002 5:35 AM
  To: [email-masked]
  Subject: [ippm] evaluating "loss constraint" for multimedia codecs

  Hi

  Best Regards