Feeding GPS Time to a Private NTP Server?

farrellj asks: "I have a customer that wants to be able to sychronise time on hundreds of servers that are spread all across the continental US and Hawaii. He was using publicly accessable NTP servers, but would rather have his own server that is not dependant on outside servers, and not have to worry about NTP based attacks. You can get a good quality and accurate time from GPS, so he looked at using a GPS reciever hooked up to a machine in his server room, but none of the GPS software out there seem to be able to just pull out the time, and then feed it to an NTP server. Has anyone tried to do this before, or know of a program that will read at GPS reciever and feed it to a NTP server process?"

Comments

Why don't people use the resources at hand?

[crath]

How to find the answer to the question the user has posed:

1. Start your browser. Don't use anything except Internet Explorer, since the answer to this question is so easily found that the asker has demonstrated that they require all the Microsoft hand-holding they can get!
2. Go to Google.com.
3. Type "GPS NTP" in the search box and click on the [search] button.
4. Read the pages pointed to in the resulting links.
5. Post apology to slashdot, for wasting everyone's time.

This has to be the lamest question in the history of "Ask Slashdot".

<Whine>

The Slashdot moderators are getting as bad as the US Patent Office. After spending many hours searching the web, I've posed much harder questions than this to "Ask Slashdot" and had them rejected.

For example, "What experiences can people share of building small sound-proof enclosures for their firewall/server kit?" Did you know that there is almost no information posted on the web, or posted to USENET, about this topic? There don't even appear to be any commercial products in this space (except for large and expensive commercial racks) for use by computer hobbiests trying to shoehorn their habit (sorry, I meant hobby) into a home shared with other people.

Come on moderators, spend a little time thinking about what you accept/reject!

</Whine>

How lame....

[CSG_SurferDude]

Note to Editors: For "ask Slashdot" posts, please at least TRY to do a "google" on the question to see if it is lame or not.

(Modded down as irrelevant/troll/slam on the editors)

GPS vs WWV

[coyote-san]

While it's true that GPS units can be used as a time standard, it's not the best solution to this problem. GPS uses satellites the power is very limited and you can't use them indoors.

A much better solution is to use a standard shortwave receiver that can pick up the digital time signal from WWV. That signal is much stronger and can probably be picked up inside most buildings (perhaps with a simple antenna) in most of the country. That's why this is the signal used by desktop "atomic clocks." You might be able to use one of them as a time source, but I would suggest checking the NTP documentation for recommendations for hardware that supports PPS signals. There's also some websites describing DIY radio receiver hardware.

The downside of this approach is that there's a propogation delay in the ground signal. GPS should give you the current time accurate to microseconds, while the radio delay may be in the milliseconds. (Ground waves are closer to a signal down a wire than a signal through free space, so the prop speed is well under 'c'.) This should not be an issue except for the most demanding uses.

Appliance

[dotslash]

There are a number of purpose built systems that are designed as highly accurate NTP stratum 1 servers, with GPS input.

These are rack-mountable 1u servers designed for service provider environments. I have deployed several such systems.

Have a look at TrueTime" for an example.

Some of these systems are Linux/ntpd/gpsd based, but come with support and in a turn-key format with Web based GUI.