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Posted by Jerry Stuckle on 07/02/07 01:24
Unruh wrote:
> ibuprofin@painkiller.example.tld (Moe Trin) writes:
>
>> On Sat, 30 Jun 2007, in the Usenet newsgroup comp.os.linux, in article
>> <dZxhi.4257$Io4.646@edtnps89>, Unruh wrote:
>
>>> ibuprofin@painkiller.example.tld (Moe Trin) writes:
>
>>>> I'd change network providers too. In the thirty-four years I've been
>>>> in networking, the longest we've been disconnected is six hours - the
>>>> classic 'backhoe fade' thanks to the city water department.
>
>>> Look, if you are really that desperate for accurate times, get a gps
>>> receiver with pps capability.
>
>> I'm not desperate for accurate times - we've been setting our servers
>> to a time standard for decades. We started by using the time ticks from
>> WWVB back in the 1970s, before we had IP. We've had GPS time receivers
>> for at least seven years, but that's in addition to the use of NTP pool
>> servers and company peers (which - surprise, surprise - also have GPS
>> receivers and use NTP pool servers).
>
>>> That will keep your system accurate to microseconds . And it will not
>>> go off when your network disconnects.
>
>> Actually, that wake-up call from the city occurred back in ~1992, and
>> prompted us to get redundant network connections in the same year. The
>> fun is verifying that your connections are indeed redundant, and not
>> running in the same conduit as leased pairs from your primary provider.
>
>>> And they are cheap ( the one I bought was less than $100) Use ntp to
>>> sync to it, not to th enetwork ( which is certainly not good to even
>>> msec, never mind microseconds).
>
>> Maybe you want to read the NTP documentation. If all you have is one
>> time source, you are indeed unable to correct for propagation delays.
>> But if you have more than that (can you say "redundancy" Bill? I
>> though you could), you can deduce and eliminate nearly all of the
>> delays.
>
> What delays? The delay between the gps receiver and the computer it is
> attached to is a usec at most.
>
You need to check your laws of physics. It's on the order of
milliseconds, at least. About 1 ms for every 186 miles to the
satellites. And the satellites are seldom directly overhead.
> However redundancy is good, esp is someone decides to disconnect your gps.
>
> I guess you meant that you have one gps receiver which acts as a stratum
> one to a whole bunch of other systems. Then yes, redundancy can be useful.
> On the other hand just put one on each critical machine and be done with
> it.
>
>
>
>>> Then slave your other computers to that one as a stratum 1 server.
>
>> -rw-rw-r-- 1 gferg ldp 43295 Nov 18 2005 TimePrecision-HOWTO
>
>>>> Thus, there are three time servers here, each monitoring _separate_
>>>> time sources, and averaging that to 'tweak' their own concept of
>>>> correct time, and we're not even subject to those regulations - they
>>>> are only serving time to 2500+ users in this facility, and acting as
>>>> a stratum 4 reference to other time servers in other company locations.
>>> Why not get a gps clock with the network as backup?
>
>> Read the docs from Dave Mills at UofDelaware. He writes pretty well.
>
> Yes, have done so. Just which point was it you wanted me to read?
>
>
>
>> Old guy
--
==================
Remove the "x" from my email address
Jerry Stuckle
JDS Computer Training Corp.
jstucklex@attglobal.net
==================
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