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Re: [PMOL] FW: IETF Draft: SIP Performance Metrics-03
Mario and Al,
Thank you for coming to agreement on the text. I will update the draft and
submit today.
Regards,
Daryl
On 3/4/09 1:39 AM, "Marian Delkinov" <marian.delkinov at ericsson.com> wrote:
> Thanks Al!
>
> IMO, the definitions you proposed are accurate and in accordance with
> RFC 2330.
>
> Best regards!
> Mario.
>
> -----Original Message-----
> From: pmol-bounces at ietf.org [mailto:pmol-bounces at ietf.org] On Behalf Of
> Al Morton
> Sent: Tuesday, 03 March, 2009 22:13
> To: Daryl Malas; pmol at ietf.org
> Subject: Re: [PMOL] FW: IETF Draft: SIP Performance Metrics-03
>
> Mario's comment is in the archive (and my In-box) so it appears to have
> been processed by the list.
>
> I think that the main question, when trying to reconcile Gerald's and
> Mario's comments, is whether we are talking about clock offset, or time
> offset and error in time offset.
>
> RFC 2330 defines clock offset in section 10.1:
> To begin, we define a clock's "offset" at a particular moment as the
> difference between the time reported by the clock and the "true"
> time
> as defined by UTC. If the clock reports a time Tc and the true time
> is Tt, then the clock's offset is Tc - Tt.
> and since 2330 is our primary reference here, that's the way we should
> go, IMO.
>
> 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 clock offset [RFC2330] is the difference
> ^^^^^
> between T1 and a recognized primary source of time, such as UTC
> (offset = T1- UTC).
>
> Same page, (approx. Mario's suggested 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 clock's offset. The clocks used at the different
> measurement points 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.
>
> Later in the same section:
>
> Time Interval Accuracy
>
> 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 one
> source of error for the measurement and is associated with the
> clock's skew [RFC2330].
>
> A stable and reasonably accurate clock is needed to make the time
> interval measurements required by this memo. This source of error
> SHOULD be constrained to less than +/- 1 ms, implying 1 part per
> 1000
> frequency accuracy for a 1 second interval.
>
> Hope this helps,
> Al
> (as a participant)
>
> At 01:52 PM 2/24/2009, Daryl Malas wrote:
>> 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.
>>>
>>>
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-----------------
Daryl Malas
CableLabs
(o) +1 303 661 3302
(f) +1 303 661 9199
mailto:d.malas at cablelabs.com