[xrblock] comment on draft-ietf-xrblock-rtcp-xr-qoe-02.txt

[Al Morton <[e-mail]>]

Regarding:
http://tools.ietf.org/id/draft-ietf-xrblock-rtcp-xr-qoe-02.txt

>    Calculation Algorithm (CALg):3 bits
>
>          000 - ITU-T P.564 Compliant Algorithm [P.564] (Voice)
>          001 - G.107 [G.107] (Voice)
>          010 - ETSI TS 101 329-5 Annex E [ ETSI] (Voice)
>          011 - ITU-T P.NAMS [P.NAMS] (Multimedia)
>          100 - ITU-T P.NBAMS [P.NBAMS] (Multimedia)
>          101~111 - Reserved for future extension.
>
>       G.107 and P.564 and ETSI TS101 329-5 specify three Calculation
>       algorithms or MoS algorithms that are used to estimate speech
>       quality or conversation quality.  P.NAMS and P.NBAMS specify two
>       MoS algorithms that are used to estimate multimedia quality
>       including video quality, audio quality and audio-video quality.

Specifying the standard for the calculation is a good start,
but these standards all have options and input parameters
that must also be specified in order to know what the MOS means.

For example, we need to know what codec was used, because G.726
carries an equipment Impairment factor that limits the upper
bound on MOS, while G.711 does not.

Some of the input parameters will be assumed (e.g., at default values)
while others will be measured, and the distinction between measured
and assumed parameters should also be made.

As I mentioned, metrics with many optional parameters are somewhat
difficult to identify in a simple way, as we found with the IPPM
Metrics Registry (which we withdrew when we found it was insufficient
to describe the measurement results in an exact way).

Colin Perkins suggested the possibility a registry for the calculation alg.
A registry could provide a single value index to a complicated set of
input parameters and other assumptions, and this might work for you.

hope this helps,
Al