[ntp:questions] NTP server near Houston?

Ron Frazier (NTP) timekeepingntplist at techstarship.com
Sun Jun 3 15:20:14 UTC 2012


Hi Bob,

Lots of good general info here:
http://ntp.org/

More specific info here:
http://support.ntp.org/bin/view/Servers/WebHome

In general, if your need is very important, and you're serving time to a bunch of other computers, you can access some stratum 1 time servers. They are connected directly to an official "source" of time, such as an atomic clock or a GPS or a radio clock. Use these only if you have to, as they are very heavily loaded.

If your needs are less severe, you can use some stratum 2 time servers. They use stratum 1 servers as their source.

Stratum 1 list:
http://support.ntp.org/bin/view/Servers/StratumOneTimeServers

Stratum 2 list:
http://support.ntp.org/bin/view/Servers/StratumTwoTimeServers

In either case, scroll down the list until you see location US or US TX. You should find some good options there. Click on each server entry to find more details about it.

You should also consider the NTP Pool project. With those servers, the routers choose one or more servers for you at random.

Info here:
http://www.pool.ntp.org/en/
http://www.pool.ntp.org/en/use.html
http://www.pool.ntp.org/zone/north-america
http://www.pool.ntp.org/zone/us

In your case, you probably want to use US specific pool servers. You can do this by putting the following in your ntp.conf file.

server 0.us.pool.ntp.org
server 1.us.pool.ntp.org
server 2.us.pool.ntp.org
server 3.us.pool.ntp.org

In my case, I have 4 servers specifically chosen from the stratum 2 list, and 4 US pool servers as indicated above. I'm located in Georgia.

As someone else said, you can set up your own stratum 1 time server by attaching a GPS to your PC and getting time from there. You can get different levels of accuracy depending on how you attach it. The GPS itself will generally have an accuracy of 1 us or better. Getting the data into the computer is the trick. From my experience, you may expect the following at the computer in Windows. Linux is better.:

Attach with USB: ~ + / - 10 ms accuracy
Warning, using this method, you are reading time data from the GPS in the form of ASCII strings, referred to as NMEA data. This data varies in it's timing on some GPS's over time by about 70 ms or so in either direction. So, overall, the solution is not very accurate and not much better than you get from the internet. However, if + / - 100 ms is good enough for you, you could use this. This still has the advantage of being able to run without internet access.

Attach with USB with PPS (pulse per second) signal to the DCD pin (pin 1) running through a USB - Serial converter: ~ + / - 1 ms accuracy

Attach with SERIAL connection with PPS to signal to the DCD pin (pin 1): ~ + / - 40 us accuracy

Once you have your own stratum 1 server running, it can serve time to other computers on your personal LAN. You want to make sure you have security restrictions in ntp.conf. I'll be glad to share mine if needed, but I'm not at that computer right now. You also want to set your software firewalls to allow ntp communication within your LAN, but not incoming from the internet without you first requesting it. In my case, the network latencies on my wifi LAN vary widely, from a few ms when idle, to hundreds of ms when heavily used. My approximate results for other computers not connected directly to the GPS are as follows:

Poll a local stratum 1 server on my LAN: ~ + / - 10 ms accuracy

Poll a remote internet server: ~ + / - 50 ms accuracy

As I said, Linux generally performs better than Windows. These results are from Windows. Some people get much better results from internet polling, depending on their network configuration.

I'm certainly not an expert on NTP, but I'd be glad to answer any questions about how I got my stratum 1 server running. It is, by the way, cross platform. So, I can boot into Windows or Linux and it still works.

Sincerely,

Ron



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Ron Frazier
timekeepingdude AT techstarship.com

bob at coolfone.comze.com wrote:

Can someone help me figure out a really good NTP server near Houston?

Thank you.

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