[PMOL] FW: IETF Draft: SIP Performance Metrics-03

["Daryl Malas" <D.Malas at cablelabs.com>]

Forwarding comments on behalf of Mario, because I never saw them hit the
mailing list...


----------------
Daryl Malas
CableLabs
(o) +1 303 661 3302
(f) +1 303 661 9199
mailto:d.malas at cablelabs.com
 

> -----Original Message-----
> From: Marian Delkinov [mailto:marian.delkinov at ericsson.com] 
> Sent: Friday, February 20, 2009 3:43 AM
> To: Daryl Malas
> Cc: pmol at ietf.org
> Subject: RE: IETF Draft: SIP Performance Metrics-03
> 
>  
> Daryl, 
> 
> Sorry, for my perhaps delayed feedback! (I'm back after a 
> long absence).
> 
> I checked the new version (03) of the draft. All the texts 
> that I had comments before are fine. 
> 
> However, I found some changes in other texts, based on other 
> people's comments, that I have to disagree with. 
> 
> ---
> Chapter 3, page 5:
> As defined above, T1 is associated with the start of a request and
>    also serves as the time-of-day stamp associated with a single
>    specific measurement.  The time offset [RFC2330] is the difference
>    between T1 and a recognized primary source of time, such as UTC
>    (offset = T1- UTC).
> 
> Instead of using the term "time offset" above, I suggest 
> "clock's offset". Thus the text will comply with the 
> terminology used in RFC2330, chapter 10.1.
> 
> ---
> Same page, the text:
> When measurement results will be correlated with other results or
>    information using time-of-day stamps, then the time clock that
>    supplies T1 SHOULD be synchronized to a primary time source, to
>    minimize the error in the time offset.  The time offset MUST be
>    reported with each measurement.
> 
> I fail to understand the sentence "to minimize the error in 
> the time offset". There is no ERROR in the time offset, 
> because the time offset IS the error. Moreover RFC2330 
> doesn't define such error, the draft doesn't define it 
> either, so better avoid using it. I suggest keeping the text 
> as in version-02, but using "clock's offset". 
> 
> In addition, when correlating measurements, it's much more 
> important all clocks used at the measurement sources to be 
> synchronized to each other, rather than be synchronized to 
> primary time source. Thus the relative offset should be minimized. 
> 
> So the text should be:
> 
> When measurement results will be correlated with other results or
>    information using time-of-day stamps, then the time clock that
>    supplies T1 SHOULD be synchronized to a primary time source, to
>    minimize clock's offset.  The clocks used at the different 
>    measurement sources SHOULD be synchronized to each other, to
>    minimize the relative offset (as defined in RFC2330). The 
>    clock's offset and the relative offset MUST be reported with 
>    each measurement.
> 
> ---
> Respectively and for the same reasons, the following text:
> The accuracy of the T4-T1 interval is also critical to maintain and
>    report.  The difference in errors between the time offsets 
> at T1 and
>    T4 is associated with the clock's skew [RFC2330].
> 
> Should be kept as in version -02, but use the "clock's offset" term:
> 
> The accuracy of the T4-T1 interval is also critical to maintain and
>    report. The difference between clock's offsets at T1 and T4 is the
>    error for the measurement and is associated with the 
> clock's skew [RFC2330].
> 
> 
> I'm OK with all other changes in version -03 compared to version -02.
> 
> Best regards!
> Mario.
> 
>