[Ntp] [Technical Errata Reported] RFC5905 (5601)
RFC Errata System <rfc-editor@rfc-editor.org> Tue, 15 January 2019 08:03 UTC
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Subject: [Ntp] [Technical Errata Reported] RFC5905 (5601)
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The following errata report has been submitted for RFC5905, "Network Time Protocol Version 4: Protocol and Algorithms Specification". -------------------------------------- You may review the report below and at: http://www.rfc-editor.org/errata/eid5601 -------------------------------------- Type: Technical Reported by: Takashi Nakamoto <takashi.nakamoto@nao.ac.jp> Section: 11.2.3. Original Text ------------- | s.rootdisp <-- p.epsilon_r + p.epsilon + | | p.psi + PHI * (s.t - p.t) | | + |THETA| | | s.refid <-- p.refid | | s.reftime <-- p.reftime | | s.t <-- p.t | +-------------------------------------------+ Figure 25: System Variables Update There is an important detail not shown. The dispersion increment (p.epsilon + p.psi + PHI * (s.t - p.t) + |THETA|) is bounded from below by MINDISP. Corrected Text -------------- | s.rootdisp <-- p.epsilon_r + p.epsilon + | | p.psi + PHI * (t_s - p.t) | | + |THETA| | | s.refid <-- p.refid | | s.reftime <-- p.reftime | | s.t <-- p.t | +-------------------------------------------+ Figure 25: System Variables Update where t_s is the time when the system variables are updated. There is an important detail not shown. The dispersion increment (p.epsilon + p.psi + PHI * (t_s - p.t) + |THETA|) is bounded from below by MINDISP. Notes ----- In the same section, it is said that "By rule, an update is discarded if its time of arrival p.t is not strictly later than the last update used s.t." This means that p.t > s.t when the system variable is updated. Hence, (s.t - p.t) is negative. It may lead to a negative dispersion, but, by definition, the dispersion cannot be negative. So, the original formula should be wrong. Because the dispersion is defined as the value that grows at constant rate PHI, s.rootdisp should be s.rootdisp <-- p.epsilon_r + p.epsilon + p.psi + PHI * (t_s - p.t) + |THETA| where t_s is the time when the system variables are updated. The symbol t_s is arbitrary because it is not defined in other places. Instructions: ------------- This erratum is currently posted as "Reported". If necessary, please use "Reply All" to discuss whether it should be verified or rejected. When a decision is reached, the verifying party can log in to change the status and edit the report, if necessary. -------------------------------------- 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 Protocol Area : Internet Stream : IETF Verifying Party : IESG
- [Ntp] [Technical Errata Reported] RFC5905 (5601) RFC Errata System