Subject: [AVT] Agenda item - Extending RTCP for Call Quality Metrics

From: "Alan Clark" <[email-masked]>
Date: Mon, 10 Dec 2001 17:24:00 -0500

Extending RTCP for call quality metrics

There is a need to both exchange QoS metrics between endpoints and provide
intermediate systems the ability to understand the end-point QoS.  Currently
RTCP provides delay, average packet loss and short term average PDV however
some applications (e.g. VoIP) are very sensitive to packet loss
distribution, to packet discards caused by jitter (and affected by dynamic
jitter buffer behavior), to changes in delay and potentially changes in
CODEC type.  In addition, packet loss mitigation algorithms such as FEC or
packet loss concealment can mask the effects of loss.  RTCP statistics as
currently implemented do not provide sufficient data for call quality to be
estimated and lose much useful information on how network impairments are
correlated - sending RTCP reports very frequently would help but would
generate network traffic.
If RTCP is extended to incorporate call quality (or other specific
application QoS) metrics calculated at the end-point then accurate
information can be provided to end and intermediate systems whilst
maintaining a fairly low rate of RTCP transmissions.  Metrics could also
properly reflect the "true" impact of network impairments on application
performance.

Alan Clark
Telchemy Incorporated
770-614-6944
[email-masked]

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