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Edits in the NTP section to address Hayden's notes

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Martin Fouilleul 2022-07-19 12:01:19 +02:00
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@ -211,10 +211,10 @@ Links: [Mills, Analysis and Simulation of the NTP On-Wire Protocols](https://www
The clock filter is a shift register containing the last 8 samples produced by the on-wire protocol. The filter algorithm selects the sample with maximum expected accuracy. It is based on the observations that: The clock filter is a shift register containing the last 8 samples produced by the on-wire protocol. The filter algorithm selects the sample with maximum expected accuracy. It is based on the observations that:
* The samples with the low [NOTE(hayden): is this meant to read 'lowest'?] network delay were likely to exhibit a low error at the time they were produced. * The samples with the lowest network delay were likely to exhibit a low error at the time they were produced.
* Older samples carry more accuracy than newer ones due to clock drift. * Older samples carry more accuracy than newer ones due to clock drift.
As a new sample is pushed to the register, it evicts the oldest sample. The dispersion values of the other samples are then incremented by $\varphi_c\times\Delta_t$, where $\Delta_t$ is the time elapsed since the last update from the server. A distance metric $\lambda_i$ is affected [NOTE(hayden): as in appended?] to each sample: As a new sample is pushed to the register, it evicts the oldest sample. The dispersion values of the other samples are then incremented by $\varphi_c\times\Delta_t$, where $\Delta_t$ is the time elapsed since the last update from the server. A distance metric $\lambda_i$ is associated to each sample:
$\lambda_i = \frac{\delta_i}{2}+\varepsilon_i \,.$ $\lambda_i = \frac{\delta_i}{2}+\varepsilon_i \,.$
@ -224,7 +224,7 @@ The peer's dispersion $\varepsilon_p$ is computed as an exponentially weighted a
$\varepsilon_p = \sum_{i=0}^{N-1}\frac{\varepsilon_i}{2^{(i+1)}} \,.$ $\varepsilon_p = \sum_{i=0}^{N-1}\frac{\varepsilon_i}{2^{(i+1)}} \,.$
The server's jitter $\psi_p$ is computed as the root mean square (RMS) of the offsets differences with respect to the offset of the first sample's in the list [NOTE(hayden): This sentence is difficult to read -- it may be because of the multiple forms of gramatical possessiveness. There also might be some typos in that regard]: The server's jitter $\psi_p$ is computed as the root mean square (RMS) of the offsets differences with respect to the offset of the first sample's in the list [NOTE(hayden): This sentence is difficult to read -- it may be because of the multiple forms of gramatical possessiveness. There also might be some typos in that regard][NOTE(martin): let me know if this one works better: The server's jitter $\psi_p$ is computed as the root mean square (RMS) of the differences of each offset with the first offset in the list]:
$\psi_p = \frac{1}{n-1}\sqrt{\sum_{i=0}^{N-1}(\theta_0-\theta_i)^2} \,.$ $\psi_p = \frac{1}{n-1}\sqrt{\sum_{i=0}^{N-1}(\theta_0-\theta_i)^2} \,.$