[time-nuts] Is it sensible to update every few seconds from NTP server?

[Bob Camp]

Hi

There are two different things being used here. One is SNTP - a one way time set and forget approach. The other is NTP - a client / server setup that creates a disciplined local clock in software. You get SNTP data from an NTP server, but that doesn't make it NTP. It's still SNTP. Since you pick a NTP server when you do SNTP setup people get confused. 

Rapid poling with SNTP is silly. Back a few thousand years ago :), desktop / laptop cpu horsepower for NTP was an issue. That hasn't been true for at least 15 years. You are doing heavy duty DSP to run any of these modes. If your CPU can do that, NTP is not going to be an issue. I doubt you will even *see* the CPU percentage used by NTP on a modern machine.

Bob

On Nov 7, 2012, at 10:04 PM, Christopher Brown <cbrown at woods.net> wrote:

> 
> There are 2 different things here.
> 
> 
> "Setting" the time based on a single query.
> 
> "Disciplining" the local clock
> 
> 
> Many of the built in NTP clients just "Set" the time every X
> 
> Setting one of these to "SET" the local clock every X seconds is a less
> than good thing.
> 
> 
> If you timing needs are loose, let the client _set_ the time once an
> hour or day.
> 
> 
> If you need tight timing, install a full NTP setup.
> 
> 
> Normally this means...
> 
> 
> Host starts up
> 
> Host performs a _set_ to get the time within a few tens of ms
> 
> Host then fires up a proper ntp server, with a list of remote service.
> This talks to all of the provided servers, figures the local osc offset,
> compensates and keeps everything in-line.
> 
> This is a much better (and more stable) setup than hard setting the
> clock every 4 seconds
> 
> On 11/7/12 12:41 PM, David Kirkby wrote:
>> Someone at my radio club uses some mode of operation where accurate
>> time is required. He said the standard Windoze clock does not keep
>> sufficiently accurate, so he has software which updates from an NTP
>> server every 4 seconds or so. It's not exactly a denial of service
>> (DOS) attack, but seems almost close to it in NTP terms to me. I can't
>> really believe updating every few seconds is sensible myself, but he
>> assures me it works very well. (I'm rather hoping it does not use a
>> stratum 1 server!)
>> 
>> I'm sure someone will say if you want accurate time on a PC, to use
>> some combination of GPS, rubidium or OCXO with a 1 pps pulse and a
>> serial port on a FreeBSD or similar computer. But that's probably not
>> practical if your software only works on Windoze.
>> 
>> Any comments?
>> 
>> Dave, G8WRB.
>> 
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