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RFC 5905, "Network Time Protocol Version 4: Protocol and Algorithms Specification", June 2010

Source of RFC: ntp (int)

Errata ID: 5600
Status: Reported
Type: Technical
Publication Format(s) : TEXT

Reported By: Takashi Nakamoto
Date Reported: 2019-01-15

Section 10. says:

   Let the first stage offset in the sorted list be theta_0; then, for
   the other stages in any order, the jitter is the RMS average

                          +-----                 -----+^1/2
                          |  n-1                      |
                          |  ---                      |
                  1       |  \                     2  |
      psi   =  -------- * |  /    (theta_0-theta_j)   |
                (n-1)     |  ---                      |
                          |  j=1                      |
                          +-----                 -----+

It should say:

   Let the first stage offset in the sorted list be theta_0; then, for
   the other stages in any order, the jitter is the RMS average

               +-----                             -----+^1/2
               |              n-1                      |
               |              ---                      |
               |    1         \                     2  |
      psi   =  | -------- *   /    (theta_0-theta_j)   |
               |  (n-1)       ---                      |
               |              j=1                      |
               +-----                             -----+

Notes:

The formula to calculate jitter "psi" in section "10. Clock Filter Algorithm" is incorrect, and also inconsistent with the formulate to calculate "psi_s" in section "11.2.2. Cluster Algorithm".

"psi" is defined as RMS average, so the term 1/(n-1) should be within [ ]^1/2 block.

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