[ntp:questions] Re: Philosophical question about strata

Brad Knowles brad at stop.mail-abuse.org
Fri Oct 14 17:49:34 UTC 2005


At 4:58 PM +0000 2005-10-14, Wolfgang S. Rupprecht wrote:

>  I was thinking more of the situation where the GPS signal wasn't
>  totally unusable but where the gps knows that it has a solution with
>  huge error bars.  In a situation like this, using the time from the
>  GPS would still be better than nothing, but just about any other
>  stratum 1,2,3 would be preferable.

	With NTP, Stratum is a binary thing.  You don't do a calculation 
to set yourself to have a worse stratum based on the error bars of 
your SYSPEER.


	By definition, your stratum is that of your SYSPEER, plus one. 
Period.  That's it.  There is no other way.

	If your SYSPEER is a Stratum 0 refclock, then however "good" or 
"bad" that refclock might be, your Stratum is 1.  Period.

	If your SYSPEER is a Stratum 2 server that has selected a 
particular Stratum 1 server as its SYSPEER, then your Stratum is 3. 
Period.



	Now, a refclock driver could choose to make use of this 
additional information and decide whether or not to declare itself 
"insane", but that's about the most you could hope for.

>  For a concrete example, sitting at a picnic table under some redwoods
>  with a gps plugged in gives one a truly awful signal.  Unless one has
>  some connection to the net (say wireless or cellphone), the only
>  available time source is that gps.  Assigning it a stratum of 5 seems
>  like it would do the right thing in terms of making it an undesirable
>  time source, but one that could still be used in a pinch.

	You're talking as if Stratum could be calculated to be a 
floating-point number, so that 5.1 is worse than 5.0, but slightly 
better than 5.11, but that's not the way it works.  Moreover, not 
only are we using integers, but we're using integers up to 15, with 
the "cliff of death" at 16.

	The kind of calculations you're talking about just do not fit 
into this model.  You might as well be speaking Greek to a Turkish 
Cypriot, or Turkish to a Greek Cypriot.

-- 
Brad Knowles, <brad at stop.mail-abuse.org>

"Those who would give up essential Liberty, to purchase a little
temporary Safety, deserve neither Liberty nor Safety."

     -- Benjamin Franklin (1706-1790), reply of the Pennsylvania
     Assembly to the Governor, November 11, 1755

   SAGE member since 1995.  See <http://www.sage.org/> for more info.



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