[time-nuts] Simple NTP server based on a Raspberry Pi

[Sarah White]

On 10/29/2012 7:53 PM, Chris Albertson wrote:
> I'm curious what load average numbers do you get if you type "uptime"
> after running NTP for some hours.   I'd guess that even on the Pi the
> CPU is hardly used at all.  That would also depend of the number of
> NTP clients you are supporting.
> 
> On Mon, Oct 29, 2012 at 12:19 PM, David J Taylor
> <david-taylor at blueyonder.co.uk> wrote:
>> I've spent the last few days getting a very simple, low-power NTP server
>> working on a Raspberry Pi.
> Chris Albertson
> Redondo Beach, California

Basically, I'm thinking this method (raspi + refclock) is a good way to
feed a handfull of public stratum 2 servers which by definition don't
have their own local refclock.

If you made your raspi stratum 1 server publicly available via
pool.ntp.org it would almost certainly be overloaded.

... Basically, I'm thinking I might do this myself once I get done
replacing my low-quality NMEA only / firmware bug / navigation mode GPS
refclock with the timing mode one I'm still working on putting together.
(this is my first time setting up an antenna of any kind / had to do
some research and make sure I ordered the right parts)

http://www.endruntechnologies.com/time_server_clients.htm

^using the example from this:

Let's assume a raspi can handle 200 packets per second without loosing
performance too badly (limited by cpu load, etc.)

Now let's assume that all clients using the raspi time server are NOT
malfunctioning, and have settled down to the default maxpoll time of
1024 seconds between updates.

Number of Clients = (Number of Packets per Second) multiplied by 1024

That would come out to a capacity of just over 200 thousand clients if
the rate at which clients send packets were uniformly distributed

... Not sure if it's reasonable to expect a raspi to handle 200
connections per second without breaking a sweat. I've not talked with
many people who tested them, so just a guess based on the example from
endrun's website which states the cpu on their hardware runs at 133mhz
so it might really be possible to handle 200 connections per second with
the 700mhz raspi.

hope this helps,
Sarah White