Brian,
I don't know where you are going on this issue. I am told the FAA does
indeed use NTP, but I don't know specifically with what application.
The NTP engineering model provides a number of tinker and tos command
options with which to control the acceptable performance envelope. The
NTP model mitigates only its sources and does not pretend in and of
itself to watch other participants in the application. This is of course
possible using the ntpq and other tools, but is not a feature of the
intended design.
My monotonically crashed airplane scenario was intended only to provoke
serious thought about the policy of forbidding step corrections as an
absolute edict. This in principle has nothing to do with the NTP design
or implementation.
Dave
Brian T. Brunner wrote:
"David L. Mills" <[EMAIL PROTECTED]> 01/27/06 12:09PM >>>
DaveM> At the very real risk of boring everybody on this list to tears, I have
DaveM> a burning agenda to expose this issue to a responsible community.
DaveM> Your flight dispatcher machines are running just fine and one of them
DaveM> suddenly veers off course by one hour. Your application is air traffic
DaveM> control. Your choices are:
This seems to cross the boundary between NTP and the application.
NTP has no way of telling whether all the machines running a particular
distributed application all have the same notion of "the time".
A significant question is whether the distributed database application
(air traffic control in this case) runs on machines that all are NTP co-peers
or co-clients of a single time server (set)?
AIUI, NTP only disciplines the local clock, and passes judgement on the
credibility
of other clocks; it does not judge itself to be the false ticker, so it can't
tell
the application that the time returned (on this machine) is hysterical, and the
application should go ask someone else.
I think it is outside NTP's current scope to implement NDC (Network Distributed
Clock)
or NTOD (Networked Time Of Day) or NTR (Network Time Reference) to provide
"the time" for all distributed application actions. Are you (David) suggesting that
the NTP project scope be broadened to embrace some concept of NTOD?
Brian Brunner
[EMAIL PROTECTED]
(610)796-5838
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