Re: SNTP server + ntpd 4.2.4 client

Hello Bill,

(Your news client often adds an extraneous =20 suffix to quotes.)

Bill Unruh wrote:

David Woolley wrote:

Noob wrote:

I've been running ntpd 4.2.4 to synchronize my system clock using remote
stratum 2 servers as a reference. (The RTT to these servers is in the
30-50 ms range.) The accuracy is in the 1-2 ms range, based on the
reported offset.

Offset doesn't tell you the accuracy, it only gives you an idea of the
variability of the error. Theoretically, the error could be as much as
15 to 25ms, plus the error from the stratum one to the stratum 2.

Agreed. The accuracy is bounded by the round trip time. The offset
fluctuations will give and estimate of those variations in round trip time.
But that time could be biased (ie outbound packets always take 10ms more
than inbound packets for example) and your clock would be biased.

Point taken.

I've been asked to evaluate the following time server, in order to reach
a better accuracy than what the current setup provides.

You are not going to get better accuracy by changing ntp program

You have apparently misread my original post. I do not plan to change ntpd.

You are going to get a better time by using a server that is closer to
you and has more predictable round trip times (ethernet, not ADSL)

This is precisely what I plan to do. Specifically, I plan to connect my box to the time server using a cross-over Ethernet cable. (My box has 4 gigabit Ethernet ports, I will devote one to NTP traffic.) The RTT is very stable at 80-85 µs.

(AFAIU, this time server implements SNTP, not the full NTP.)

Then it is not a server.

I don't understand the point you are trying to make.
It is an SNTP server.

You will never get your network ntp under a few ms.

Unless the stratum 1 server is on the same LAN...
(As you state later.)

The idea would be to put this (stratum 1) time server in the same LAN as
my box, and add it my ntp.conf. (The RTT on the LAN is on the order of

It is NOT a stratum 1.
A stratum 1 gets its time from an atomic clock.

I don't understand the point you are trying to make.

The time server has a GPS receiver, thus it is "attached" to a
stratum 0 device, thus it is a stratum 1 server.

If you attach a GPS to one of your (Linux) machines, you will get 2 µs
accuracy on that machine. On the machines attached on your LAN you will
get 10s of µs accuracy, if they are unix type machines.

This is the setup I've been discussing, with the GPS receiver inside the "time server" I'm supposed to evaluate...

As far as I know
windows does not impliment a proper clock control API so you will have be
happy with a few msec for those.

I should have made clear that I am not using Windows.
The system to be synchronized runs Linux 2.6.22.1-rt9 and ntpd 4.2.4

Regards.
.

Relevant Pages

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