Subject: [AVT] MSF Liaison on XR drafts

From: Tom Taylor <[email-masked]>
Date: Wed, 22 Jul 2009 09:16:21 -0400

The MultiService Forum (MSF) has kindly sent a liaison providing comments on the 
RTCP-XR drafts. The text of this liaison follows. Could the authors (and, of 
course, other interested parties) please respond.

Tom Taylor

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The MultiService Forum (MSF - http://www.msforum.org/) is a global association 
of service providers and system suppliers committed to developing and promoting 
open-architecture, multiservice switching systems.  The MSF defines a physical 
architecture developed from current standards in order to combine logical 
functionality into physical nodes, thus reducing the number of interfaces 
required in an architecture.  The result identifies the specific interfaces that 
are required to be "Open Interfaces" to enable multi-vendor deployments.  The 
MSF then performs Interoperability Testing on these interfaces, thus ensuring 
that multi-vendor deployment strategies can be realised.

As part of this work the MSF is currently looking at the measurement of 
statistics and quality for voice and multimedia within carrier networks and 
between carrier networks. The MSF believes that the work currently being done 
within the IETF Audio/Video Transport working group on RTCP metrics is a 
critical component of this solution.

The MSF has conducted an analysis of the new RTCP XR report blocks that have 
been created to support high resolution reports within the context of 
identifying a minimal critical set of measurable metrics that will enable call 
quality to be assessed and recorded. As part of this analysis the MSF has 
identified the following points that it would like to pass to the IETF AVT 
working group for their consideration.

1.The MSF notes that many of these report blocks use milliseconds to report 
durations. However the sampling rate for the system is typically one every 125 
micro seconds. This means some errors will go unreported if milliseconds are 
used for these time values unless non-integer values are used. As a result of 
this some report blocks define complex data types (binary fractions) which will 
add complexity to implementations at the RTP end points and translator nodes. 
This complexity could be avoided if the values defined in the report blocks were 
based on RTP timestamp units, this would permit the use of integer data types 
with sufficient precision to report performance. Please could the IETF consider 
using RTP timestamp units rather than milliseconds in the report blocks.

2.With respect to draft-ietf-avt-rtcp-xr-pdv the MSF would ask the IETF whether 
there is a need to express the PDV performance in terms of a percentage or 
whether it might not be preferable and simpler just to report the number of 
packets that exceed a given threshold.

3.With respect to draft-ietf-avt-rtcp-xr-loss-conceal the MSF would like to ask 
the IETF if they would consider moving the metric for “Buffer adjustment 
concealment duration” into the jitter buffer report block as this metric is 
primarily a measure of jitter buffer performance.

4.With respect to draft-ietf-avt-xr-jb the MSF suggests that there may be some 
value in adding a metric for the number of jitter buffer adaptation events that 
have taken place in the interval to the report block.

5.With respect to draft-ietf-avt-xr-jb the MSF suggests that there is limited 
value in providing instantaneous results for jitter buffer nominal and jitter 
buffer maximum values. In order to simplify the RTCP metrics could the IETF 
consider removing these from the jitter buffer report block ?

6.With respect to draft-ietf-avt-xr-delay the MSF is not convinced that there is 
sufficient benefit in providing a metric for end system delay because of the 
impact of the jitter buffer behaviour on this metric. Please could the IETF 
consider removing this metric from the delay block. If the IETF believe that 
this metric is useful then the MSF would prefer it had its own separate report 
block.

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