Re: [Ntp] [EXT] [Errata Verified] RFC5905 (5020)

[Dieter Sibold <[e-mail]>]

Hi Erik and Steven, I deeply apology. Indeed I was wrong with attesting that the errata is right. Instead, I’m convinced that it is wrong. I suppose that the person who filed the errata did the same mistake as I did yesterday, i.e. I mixed up the formulas for time offset and network delay calculation.

Sometimes a fast answer is not always the best answer.

Again, sorry for the confusion.

Dieter





On 28 Jul 2022, at 10:18, Steven Sommars wrote:

> I don't get it.
>
> Theta is "the offset of B relative to A". The proposed revision is
>    1/2 * [(T2-T1) + (T4-T3)]
> Example: Let's assume that B and A are exactly synced to UTC and that the
> network delay is 50msec in each direction.
>     T2-T1 is the NTP mode 3 request delay (including network delay).
> This gives 50 msec
>     T4-T3 is the NTP mode 4 response delay (including network delay).
>  This gives 50 msec.
> The proposed revision gives 100msec/2 = RTT/2, not the expected offset of
> zero.
>
> The RFC5905 formula seems correct.
>
>     theta = T(B) - T(A) = 1/2 * [(T2-T1) + (T3-T4)]
>
> but might have been clearer had it been written:
>
>     theta = T(B) - T(A) = 1/2 * [(T2-T1) - (T4-T3)]
>
>
>
> On Thu, Jul 28, 2022 at 4:54 AM Ulrich Windl <
> [e-mail]> wrote:
>
>>>>> RFC Errata System <[e-mail]> schrieb am 27.07.2022 um
>> 17:06 in
>> Nachricht <[e-mail]>:
>>> The following errata report has been verified for RFC5905,
>>> "Network Time Protocol Version 4: Protocol and Algorithms
>> Specification".
>>>
>>> --------------------------------------
>>> You may review the report below and at:
>>> https://www.rfc-editor.org/errata/eid5020
>>>
>>> --------------------------------------
>>> Status: Verified
>>> Type: Technical
>>>
>>> Reported by: Ferenc Wágner <[e-mail]>
>>> Date Reported: 2017-05-15
>>> Verified by: Erik Kline (IESG)
>>>
>>> Section: 8
>>>
>>> Original Text
>>> -------------
>>> theta = T(B) - T(A) = 1/2 * [(T2-T1) + (T3-T4)]
>>>
>>> Corrected Text
>>> --------------
>>> theta = T(B) - T(A) = 1/2 * [(T2-T1) + (T4-T3)]
>>
>> If that's wrong, RFC 1305 would be just as wrong, because it says (page 25
>> in
>> PDF):
>> ((Ti−2 − Ti−3) + (Ti−1 − Ti)) / 2
>> ,
>>
>>>
>>> Notes
>>> -----
>>> The corresponding code line in A.5.1.1. agrees with this correction:
>>>
>>> offset = (LFP2D(r->rec - r->org) + LFP2D(r->dst - r->xmt)) / 2;
>>>
>>> taking Figure 7 into account:
>>>
>>> | org       | T1         | origin timestamp      |
>>> | rec       | T2         | receive timestamp     |
>>> | xmt       | T3         | transmit timestamp    |
>>> | dst       | T4         | destination timestamp |
>>>
>>> --------------------------------------
>>> RFC5905 (draft-ietf-ntp-ntpv4-proto-13)
>>> --------------------------------------
>>> Title               : Network Time Protocol Version 4: Protocol and
>>> Algorithms Specification
>>> Publication Date    : June 2010
>>> Author(s)           : D. Mills, J. Martin, Ed., J. Burbank, W. Kasch
>>> Category            : PROPOSED STANDARD
>>> Source              : Network Time Protocols
>>> Area                : Internet
>>> Stream              : IETF
>>> Verifying Party     : IESG
>>>
>>> _______________________________________________
>>> ntp mailing list
>>> [e-mail]
>>> https://www.ietf.org/mailman/listinfo/ntp
>>
>>
>>
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