[Ntp] Antw: [EXT] [Errata Held for Document Update] RFC5905 (5604)

Hi!

I just wonder whether "If we assume that the offset value follows the uniform
distribution" is a valid assumption; if it's not, then factor 5 can mean a
quite different thing.

Regards,
Ulrich

>>> RFC Errata System <rfc-editor@rfc-editor.org> schrieb am 26.09.2022 um
02:23 in
Nachricht <20220926002359.A68EE4C956@rfcpa.amsl.com>:
> The following errata report has been held for document update 
> 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/eid5604 
> 
> ‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑
> Status: Held for Document Update
> Type: Technical
> 
> Reported by: Takashi Nakamoto <takashi.nakamoto@nao.ac.jp>
> Date Reported: 2019‑01‑15
> Held by: Erik Kline (IESG)
> 
> Section: 11.2.3.
> 
> Original Text
> ‑‑‑‑‑‑‑‑‑‑‑‑‑
>                   | s.rootdisp  <‑‑ p.epsilon_r + p.epsilon + |
>                   |                 p.psi + PHI * (s.t ‑ p.t) |
>                   |                 + |THETA|                 |
> 
> Corrected Text
> ‑‑‑‑‑‑‑‑‑‑‑‑‑‑
>                   | s.rootdisp  <‑‑ p.epsilon_r + p.epsilon   |
>                   |                 + 5 * p.psi +             |
>                   |                 + PHI * (s.t ‑ p.t)       |
>                   |                 + |THETA|                 |
> 
> 
> Notes
> ‑‑‑‑‑
> In addition to the correction proposed in Errata ID 5601, I think that the 
> formula to calculate the dispersion should be revised. The term "p.psi" 
> should be multiplied by not one, but a larger value.
> 
> This is because the dispersion is defined as the statistics that represent 
> the maximum error, so when it is calculated, it should take into account the

> maximum errors in the offset estimation. However, the jitter p.psi is
defined 
> as the RMS average of the offset values theta_j relative to theta_0, so the

> term "p.psi" does not represent the maximum error caused by the distribution

> of the offset values.
> 
> If we assume that the offset value follows the uniform distribution, the 
> error bound is represented as sqrt(3) * p.psi. So, at least, the term
"p.psi" 
> should be multiplied by sqrt(3). There is arbitrarity in choice of the 
> distribution type, so depending on the distribution type the factor may 
> change. For example, if the normal distribution is assumed, 5 * p.psi gives

> us 99.99994% confidence. Assuming that the system variable is updated every

> 16 seconds, the actual offset may be outside the range [theta_0 ‑ 5 * p.psi,

> theta_0 + 5 * p.psi] approximately once a year. It should be sufficient for

> usual Internet applications, though someone may think that the factor "5"
may 
> not be sufficient depending on the application.
> 
> ‑‑‑
> 
> [INT AD notes]
> 
> See also 
> https://mailarchive.ietf.org/arch/msg/ntp/Cbg3sOhChyfenYoj7UG5wCymFMU/ :
> 
> """
> ...That makes some sense to me, but I'd say it really depends on the model 
> of the clock and that's arbitrary...
> """
> 
> 
> ‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑
> 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
> 
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