Re: strange behaviour of ntp peerstats entries.

Richard B. Gilbert wrote:
Maarten Wiltink wrote:
"Richard B. Gilbert" <rgilbert88@xxxxxxxxxxx> wrote in message
news:479F8551.5000505@xxxxxxxxxxxxxx
[...]

I can imagine an RTT of 60-70ms. What I have difficulty imagining is
using such a source to synch with.


Pfft. Kids these days.

(There's nothing wrong with an RTT of 60 to 70 ms per se. For example, if
it were always exactly 65 ms, that would probably be an *excellent* time
source. The problem is the jitter, and as the example of the four possible
paths along the two possible routes shows, even that can, under the right
circumstances, be solved.)

Groetjes,
Maarten Wiltink



Well, since the maximum error in transmitting time from server to client is one half the round trip delay, it is usually wise to try to minimize that delay. A server in Tokyo might have the time correct to within 50 nanoseconds but that does me little good in New Jersey! The network path would be so long and pass through so many routers and switches that by the time it gets to me, the uncertainty will be a substantial fraction of a second.

Usually, the number of possible paths will be far greater than four!

The ultimate test is the actual performance under the stated conditions.
Based on general principles, the stated conditions are NOT where I would look first for best performance.


Which is why NTP prefers the source with the smallest delay. The system
I am using has servers whose delays are 51ms to 94. I can't find any
closer. On my company LAN, the delays range from 16ms to 87ms. The
offsets of all these servers agree to within 9ms. Sure, I am not
going to get sub-millisecond from that, but I think it is probably
more typical than your set-up.

Brian Utterback
.

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