At 10:46 AM -0500 2005-09-09, wayne wrote:
Links that cross oceans tend to have high jitter and high latency.
Ending up with an NTP server that is half way around the world is
going to cause you to have something like a 100ms minimum delay.
(65ms for the speed of light, but electric signals only travel at
2/3c, plus router delays, etc.)
Then links that go across the ocean once and then come back
across the ocean, in order to get from one country to the one next
door, would be at least twice as bad. Yet this is still the case
today amongst many sites in Asia -- they have really, really bad
connectivity with each other, and much better connectivity with the
US. Until relatively recently, if you wanted to go from Korea to
Japan, all those packets would be routed via San Francisco.
You cannot make assumptions about how traffic will flow
topographically within a given geographical region. And the worst
possible mistake you could make would be to build them into
pool.ntp.org.
I know a guy in Maritius (just off the coast of Africa) that is
topologically closer to sites in Europe and the US than than he is
anything else, including two sites in Africa that have recently come
onto the radar.
There can be no substitute for good configuration on the part of
a knowledgeable local administrator. We shouldn't try to
second-guess them. We should provide as much information as we
reasonably can regarding where these servers are located
geographically, and we should leave the rest up to them.
Even filling in with random servers from around the world will allow
for automated config scripts to work today.
And those automated scripts could just as easily use
0.pool.ntp.org, 1.pool.ntp.org, etc..., without causing us any
additional work, without the likelihood of creating more network
topological problems than they can resolve, and without messing up
anything for the future.
Despite being about the same longitude, I'm pretty sure that the
people in Peru use a different timezone than the people in Maine,
mostly due to daylight savings time differnces.
Here's a hint -- NTP works exclusively in UTC. It doesn't know
about time zones. It doesn't care about time zones. So long as the
server is accurate and precise, and the latency between you is
reasonably predictable, that will be a better server for you than
many others.
There are many more than 24 timezones. While timezones aren't perfect
dividers for our purposes, they aren't too bad either.
Many servers in Europe fall into the CEST timezone, and yet many
of those countries have poor connectivity with Belgium. I am much
better off choosing servers in nearby countries that I know have good
low-latency connectivity with the country I live in, than depending
on a system that is blindly assigning me servers based exclusively on
what timezone I'm in.
Timezone helps in places like Russia, where they have a single
country that covers eleven timezones. That's a wide enough
geographic spread, over relatively poor communications
infrastructure, that a client on Sakhalin island near Japan would be
very poorly served by a server sitting in Moscow.
But in my experience, timezone provides poor solutions more often
than knowing what country you're in. This is because most countries
are pretty good at ensuring that they have reasonably good
connectivity to all parts of their country, regardless of how many
timezones it covers. But they don't necessarily have good
connectivity to other countries that might be nearby and share at
least some of the same timezones, in part because of old nationalist
rivalries that might go back hundreds or thousands of years.
--
Brad Knowles, <[EMAIL PROTECTED]>
"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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