[ntp:questions] simple nt.conf cases for ntp-client

Brian Inglis Brian.Inglis at SystematicSw.ab.ca
Fri Jan 24 19:31:11 UTC 2014


On 2014-01-24 10:42, William Unruh wrote:
> On 2014-01-23, David Woolley <david at ex.djwhome.demon.invalid> wrote:
>> On 23/01/14 13:06, Marco Marongiu wrote:
>>
>>>
>>> 3) second filter: a new value for the error that fits the majority of
>>> these C references is calculated; the L references that don't fit in
>>> this error interval are called "outlyers"; the S=C-L references that
>>> remain are considered;
>>
>> Ones that don't fall within the the largest mutually consistent set of
>> error bounds are called "false tickers", not "outlyers".
>>>
>>> 4) peer selection: among the references in S, the one that has the
>>> smallest dispersion is selected, and ntpd will "follow" it until the
>>> next evaluation of the data collected from the sources.
>>
>> This is used for the figurehead peer that defines the stratum and error
>> statistics.  All the ones that are valid and not outlyers or false
>> tickers will be tracked for time synchronisation purposes.  (The is a
>> hysteresis mechanism that means that the system peer will not change as
>> often as the description implies.)
>
> Does it use the time from that one, or some sort of "average"? Since the
> queries of the different servers occur at different times (separated by
> about and hour, given the initial filter  at poll 10) how does it take the averagei
> if it uses the average?

Every packet received goes thru the processes below and may update the system clock.
[adapted from How NTP Works http://www.eecis.udel.edu/~mills/ntp/html/warp.html#arch]

NTP Software Architecture

  Remote       Peer/Poll                 System             Clock
  Servers      Processes                 Process          Discipline
                                                           Process
+--------+. +-----------+. +------------+               .
|        |->|           |. |            |               .
|Server 1|  |Peer/Poll 1|->|            |               .
|        |<-|           |. |            |               .
+--------+. +-----------+. |            |               .
           .       ^      . |            |               .
           .       |      . |            |               .
+--------+. +-----------+. |            |  +-----------+.
|        |->|           |. | Selection  |->|           |. +------+
|Server 2|  |Peer/Poll 2|->|    and     |  | Combine   |->| Loop |
|        |<-|           |. | Cluster    |  | Algorithm |. |Filter|
+--------+. +-----------+. | Algorithms |->|           |. +------+
           .       ^      . |            |  +-----------+.    |
           .       |      . |            |               .    |
+--------+. +-----------+. |            |               .    |
|        |->|           |. |            |               .    |
|Server 3|  |Peer/Poll 3|->|            |               .    |
|        |<-|           |. |            |               .    |
+--------+. +-----------+. +------------+               .    |
...................^.........................................|.....
                    |                                    .    V
                    |                                    . +-----+
                    +--------------------------------------| VFO |
                                                           +-----+
                                                            Clock
                                                            Adjust
                                                            Process
-- 
Take care. Thanks, Brian Inglis


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