[ntp:questions] Re: Mother Of All Clocks

Heiko Gerstung hg at heiko-gerstung.de
Mon Mar 28 09:10:57 UTC 2005


Hi!

Todd Knarr <tknarr at silverglass.org> wrote in message news:<z3D1e.19692$le4.1774 at fed1read04>...
> In comp.protocols.time.ntp <88e50c98.0503261447.2849adc7 at posting.google.com> Heiko Gerstung <hg at heiko-gerstung.de> wrote:
> > several millions of transactions per day. It is simply necessary for
> > them to ensure that all their networks (which are physically separated
> > due to security reasons) including all database servers, workstations
> > and routers are running with the same time coming from the same clock.
> 
> That wouldn't completely explain the need for that many stratum-1
> servers, though. The only way I can see a need for 30+ stratum-1 sources
> is if the timestamp requirements were so stringent that you _had_ to
> have all clients sync'd directly to a stratum-1 to meet them and you had
> so many clients that you needed that many servers to avoid overload. I'd
> also want the stratum-1s physically seperated so loss of power or damage
> to a rack didn't take down all my time sources at once.
> 

They have 16 physically separated networks meeting each other in this
one server room and yes, their time stamp requirements are _very_
stringent. Of course there is a protection against the loss of power
(UPS) and other problems.

> Normally I'd have expected a dozen or so stratum-1s scattered around the
> country syncing with each other (over their own dedicated network in
> this case), and a number (depending on the number of clients) of
> stratum-2 servers for each network that needs time service multi-homed
> between the stratum-1 network and the network they serve and syncing to
> non-overlapping subsets of the stratum-1s and sibling stratum-2s. I'd
> expect that to give you better resistance to failure (short of failure
> of the GPS system itself) and be cheaper as well. The only issue would
> be time stability, which I'd expect to be on the order of no more than a
> millisecond variation between the stratum-2s in this setup.

As I explained, their networks are located in one building complex, so
it would not make much sense to use 16 single stratum 1 servers (and
it would definetly lead to higher costs!). And, the policy of this
organization prohibits any physical network connections, they fear
that a bug in the OS or whatever could be used to enabled routing
where it should not happen, so connection the stratum 1's in a
dedicated time server network and then connect the several productive
networks to a node in this time server network would be against their
policy (note: it is useless to discuss whether this policy is actually
making sense or not, we are not in the position to change it).

The protection against a failure of the GPS comes from the hybrid
reception system, which includes a DCF77 correlation receiver (the
german radio time system based on an AM transmitter).

Kind regards,
Heiko



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