For some reason recent messages seem not to be sent by the reflector (?) hence I am forwarding this directly

Alan

-----Original Message----- From: Alan Clark [mailto:alan@telchemy.com] Sent: Friday, November 08, 2002 12:29 PM To: 'frank.derks@philips.com' Cc: 'ITU-SG16@echo.jf.INTEL.COM' Subject: RE: Use of RTCP statistics for estimating QoS of VoIP

Frank

I did suggest (via Mike Buckley) that the following be added to H.460.9 however don't know if it was actually included.

" It should be noted that RTCP reports were not originally intended to provide accurate QoS metrics but for informative exchanges between endpoints to support possible dynamic configuration. According to RFC1889 (a) received packet count may include duplicate packets and hence it is possible to report negative packet loss (b) reported mean packet-to-packet delay variation (jitter) is averaged over the last 16 received packets and hence provides information only on the 160-480mS period immediately preceding transmission of the RTCP report."

I do agree with you that potential implementors may well feel uncomfortable that the Recommendation in its initial form contains information that has little or no value. I am even more concerned that less well informed implementors may accept what is in the Recommendation as being "sufficient" and hence attempt to manage VoIP services with metrics that can be quite misleading.

Regards

Alan

-----Original Message----- From: frank.derks@philips.com [mailto:frank.derks@philips.com] Sent: Friday, November 08, 2002 2:46 AM To: alan@TELCHEMY.COM Cc: ITU-SG16@echo.jf.INTEL.COM Subject: Re: Use of RTCP statistics for estimating QoS of VoIP

Alan,

I certainly agree that, if the main body of the Recommendation covers metrics that are of little practical use of the recipient of these metrics, the Recommendation can be misleading. Only with the proper background information will the reader be able to distinguish the real value in the particular metrics.

I feel somewhat uncomfortable when the main body of a Recommendation provides me with something that is of little value, but which can be extended to include more useful information.

A possible way "out of this", is to include some text that clearly explains the situation and that reflects the concerns that were raised and agreed upon.

Regards,

Frank