PSN-L Email List Message

Subject: RE: Network time standard
From: "Keith Payea" kpayea@...........
Date: Mon, 11 Apr 2005 09:53:10 -0700

I use NTPTime:, which I found
by visiting and looking for Windows 2k compatible builds of NTP.
If you are looking for a Linux version, there are many.  Go to and
poke around.

According to the log files, NTPTime is checking once an hour, and it is
adjusting the clock about +- 20 mS each time.  My computer is always on, and
I have DSL, so it can check whenever it wants.  However, my "Office" has no
temperature control, so NTPTime is able to deal with that fairly well.  

For the purposes of seismic monitoring, I'm assuming the computer is always
on.  Someone mentioned how bad the time is when the computer is off.  Also,
there was some mention of Millenium Edition.  If you can manage it, dump
that in favor of something else.  Even Microsoft admits it was not their
finest effort.....

There are also problems with Microsoft's implementation of NTP in Windows.
They have ignored the standard in a couple of places, so it can't get time
from some of the public servers.

AboutTime cited below appears to be an SNTP client, which also supports some
of the older (TIME and DAYTIME) protocols.  It's fine for getting you to a
second or better. 

As I mentioned in my previous post, a good NTP implementation will
compensate somewhat for transmission delays.  This is done by using four
time stamps:  1) at the time the request is sent, 2) at the time the request
is received, 3) at the time the response is sent, 4) at the time the
response is received.  The NTP packet has room for all four, so the client
gets them all back.  From that, the bulk of the transmission time can be
removed, and the true offset between the client and the server can be
calculated.  Things that cause it problems are if the message takes a
radically different route in each direction.  The odds of this happening
increase with distance, so that's why a nearer time server is a better
choice than a "better" server that is farther away.  Routing changes
relatively slowly based on demand.  This is also why the best
implementations need to filter the offset over several messages.  They then
adjust the system clock speed (not the crystal, just the interrupt rate!) to
compensate - they don't just jam the new time into the clock.

Before flaming me about any of my simplifications, remember to check and read through their stuff.  They have put a huge amount of
work into solving this problem while working around the OS limitations.


-----Original Message-----
From: psn-l-request@.............. [mailto:psn-l-request@............... On
Behalf Of John or Jan Lahr
Sent: Saturday, April 09, 2005 4:51 PM
To: psn-l@..............
Subject: RE: Network time standard

At 02:53 PM 4/9/2005, Keith wrote:
>Not all NTP clients are created equal...

In your experience, which is the best, free time-sync software for a PC with
an Internet connection but no local time server.

Can you evaluate 
AboutTime: ?



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