Axonn wrote:
Hi everybody. My name is Axonn Echysttas and I'm a newbie to NTP. I'm
currently working at developing a replacement for the Windows OS
Systray clock. This program is free and I've been working on it for
the past year a lot. It will enter Beta 2 no later than 25 January this
year and Beta 3 (which will be public) probably during March this year.
However, for the time being, even though I built a lot of functionality
and it looks quite nice (very flexible and customizable), I didn't
yet start on NTP time synchronization. I got the RFC about NTP and it
scared me a little to see all those math formulae in it. On
http://tf.nist.gov/service/its.htm I read that "The NIST servers
listen for a NTP request on port 123, and respond by sending a udp/ip
data packet in the NTP format. The data packet includes a 64-bit
timestamp containing the time in UTC seconds since January 1, 1900 with
a resolution of 200 ps."
My question is this: could you help me for a good cause? I would like
to know how does the NTP format look like and how to take an accurate
time out of it. I suppose I can always start reading and searching by
myself, of course. But this thing doesn't look very easy at the first
glance. Also, the amount of documentation on NTP seems huge. I don't
know if the client-side NTP involves a lot of math but if it does,
I'm not that good at math yet. I didn't yet graduate University and
my school is on freeze for the last two years since I need to work to
sustain my family. However, this project of mine I did in my free time
and for the pleasure of doing something good and helping others, I will
never request money for it.
So how can I synchronize with a NTP server or more NTP servers? Is it
so hard as I imagine after going a little through the FAQs? I would
hope that the hard part is for servers, not for clients. I await your
answers with great anticipation.
Thank you very much for your time,
Axonn Echysttas,
ASD Clock creator.
I think you ask too much! The packet format is documented in RFC 1305
on pages 50 et. seq. The formula used to compensate for transmission
delay will be found on page 100. That should be enough to get you a
time correct within, say, fifty milliseconds by querying a single
server, interpreting the reply packet and stuffing the resulting time
into your clock.
There is a freely available reference implementation of ntpd and
associated utilities. There is even a pre-built version available for
Windoze. If you want real accuracy, you will need to implement the
entire package or use the reference implementation. With a very good
server and low network latencies, ntpd is capable of synchronizing a
client within a few microseconds
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