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Network Time Syncronization via GPS?
TrAvELAr asks: "I run a rather large network for a research company and I have been tasked with a project to ensure that the time is accurate on all of our studies. Right now, I am using the time service built into Windows 2000 to sync all of our workstations with one of our servers. My problem lies in the fact that I can't prove that the time on my server is accurate. Because of the nature of our research, our network is not allowed to access the internet, thus ruling out synchronization to NIST and other time servers. I've been toying around with the idea of syncing it via GPS. I've done some research on the net and found a couple of places that offer packages for this at a fairly high price. I believe that this is something that I could do myself if I could find the right interface software. Has anyone out there had any experience with this type of project? I would appreciate any feedback/suggestions from anyone out there who has implemented/maintained a similar system."
Windows net time
Real synching of clocks can be done with NTP, the network time protocol. And yes, it can sync one computer's time to GPS...
Read the FAQ for more information... and the newsgroup comp.protocols.time.ntp is read by many helpful people! .
Here is one from NIST, detailing differnt ways (you could always use a modem, the cheap route):http://www.boulder.nist.gov/timefreq/genera l/pdf/834.pdf
And here is a German company that makes a ISA card:http://www.quancom.de/quancom/quancom01.nsf/
We run a secure datacentre and provide a Stratum-1 time source using a Lantronix Network Time Server (CoBox-NTP-E1) [about $1,500.]. It is a network-attached device with an IP that broadcasts the time to a second level time server. It has an attached cable that goes to a GPS antenna that receives the signal. The only problem with these devices is that the antenna obviously has to be _outside_ of the computer room to get a good signal, which can be a problem with some people who have already sealed up their Lampertz bunkers!
Anyways, it works great, no signal drift, and, as a previous poster mentioned, NTP is a MUST to ensure that the signals on all the Windows domains, firewalls, switches and anything else looking at the Stratum-2 server don't drift in their own merry direction with periodic "violent" recorrections to the correct time.
There are 3 excellent white papers from SUN detailing how NTP works, which is much more complex than you might initially think. See:
http://www.sun.com/blueprints/0701/NTP.pdf
http://www.sun.com/blueprints/0801/NTPpt2.pdf
http://www.sun.com/blueprints/0901/NTPpt3.pdf
for good info on how to do this properly. Lots of fun!
-wjc.
"I figure you're here 'cause you need some whacko who's willing to stick his finger in the fan. So who are we helping?
I use the Lantronix CoBox E1.
It's relatively inexpensive (~$1500 w/GPS antenna and cable last time I checked) and seems to work well.
The best way to set this particular box up is to have ntp running on a regular server, and have that server get it's updates from this box while other clients get their update from the server. This unit doesn't seem to scale well to provide a time source for a lot of clients.
If you're really paranoid, you could simultaneously set up a system to check NIST signals for time and then let GPS and NIST duke it out in your ntp server.
"But actually trying to use m4 as a general-purpose langage would be deeply perverse" --ESR
I've never owned one of these things, but a company called Exit Consulting claim to make a GPS clock accurate to a millionth of a second. Suprisingly enough the URL for their product is http://www.gpsclock.com/ :> The price is about $380usd for a unit (some assembly required), and they provide everything you need to get this running as a Stratum 1 NTP server.
:wq
How much accuracy do you need?
Every GPS on the market with a serial port outputs NMEA format messages (well, almost all, check before you buy). Those messages contain the current time in nice easy-to-read ANSI text.
Here's an example:
$GPGGA,162245.00,4842.6942,N,11342.9476,W,1,05,
The second field there is the time HHMMSS.SS. Here's a link to the NMEA protocol:
http://www.starlinkdgps.com/manuals/invictaprot
If you need more accuracy than that, you could get a GPS with a 1PPS output - the Motorola Oncore series comes to mind. Prices are pretty cheap, though not as cheap as your average consumer model. Tie the 1PPS output to a serial port's DTR line and write a small driver to read the value. Latency of that driver is the prime determinate of your accuracy at that point.
1. 2.
Hello. If you are a do-it-yourselfer, I wrote the programs that you can find at:
http://www.floatingdoghead.net/source
The TractorBeam program with my mod to serial.c for the 2.2.19 kernel is posted there. This is free hackware under the GPL. It works in conjunction with the affordable Delorme EarthMate GPS receiver.
I have not worked on this code for over a year, so I'm a little rusty on it. I never tested what happens when DST kicks in, but as I remember, all computations are done in regards to UTC, so it may be a non-issue. I keep my firewall set to UTC as a matter of course. This program (and the associated kernel module) keep the clock swings within a couple of mS. You may need to apply a delta correction if you are concerned with absolute synchronization. When I wrote this, I was more concerned with eliminating drift as much as possible, and not in attaining absolute time sync.
Cheers.
2 years ago I wrote a small C program to synchronize a Windows PC to a Trimble GPS: easy. A RS232 library, a quick look at the Trimble communication protocol and it was done in under 4 hours.
Last week I've been synching my SGIs using ntp (Network Time Protocol) and I saw in the documentation that it can also synch to a GPS. Didn't look at the details though, but probably through the serial port. And ntp is free.
Non-Linux Penguins ?
Back in the mid-80s, HeathKit used to sell a clock kit that would sync to the RF time broadcasts from the atomic clock in Ft. Collins. A little googling around yielded this link and this link and also this link (those last two look like they could be different fronts for 1 company). It's a "cooler" design than the old HeathKit one, which was blocky and looked like a typical "kit" deal, and I'd probably call to make sure it just sends a burst of ascii data down the serial port if you feel like rolling your own software, but it seems to come with Dos, Win3.1, 95/98, and NT software, as well as docs on the exchange protocol the clock uses. At $100, it's probably one of the cheaper solutions out there, and assuming you have a free serial port (which it sounds like if you're planning to use GPS), probably a fairly painless operation.
:-)
Now that I think about it, I might get one of these for myself, and stop relying on NTP.
"The urge to save humanity is almost always a false front for the urge to rule." --H.L. Mencken
I belive you can get a PCI card that tunes to the attomic clock.
seems like it would be cheaper not to mention easyer. no cables to run or hook up and less software to configure.
doing it via gps would be a cool hack though.
Check out http://www.analogx.com/contents/download/network/a ts.htm, the program can get it's time from you, the NIST servers (i.e. use a laptop to get the time from the internet and then use it's corrected time to set the time on your primary server.) or from your GPS solution.