[time-nuts] Raspberry Pi tweaks and custom kernel, was RE: PPS for NTP Server - How Close Is "Good Enough"?

Bob Camp kb8tq at n1k.org
Tue Jun 16 07:05:11 EDT 2015


Hi

> On Jun 15, 2015, at 9:38 PM, Chris Caudle <chris at chriscaudle.org> wrote:
> 
> On Mon, June 15, 2015 8:01 pm, Bob Camp wrote:
>> Unless you have fancy switches on your LAN (1588 stamping), PTP
>> performance will be dependent on load and the "goodness" of the switches
> you do
>> have. These are pretty much the same (external)  things that impact NTP.
> 
> Yes, but proper differentiated services setup with multiple queues can
> help mitigate that to a large extent.  I'm still trying to get my PTP
> setup going, so I don't have any measurements of my own yet, but there are
> lots of examples of large commercial systems in use without transparent
> clock support which can maintain sub-microsecond synchronization.  Using
> PTP transparent switches should get down into the couple hundred
> nanosecond range or better, but even without 800 or so nanoseconds has
> been shown to be consistently possible.
> I have no idea what level of synchronization you could keep using just NTP
> with diffserv.

I believe that you can do exactly that. Once you take the stamping switches
out of the mix there isn’t a lot of difference between the two protocols. You would
indeed need to tweak NTP a bit, but that part of the fun.

Bob

>  That might be an interesting experiment to try for those
> who only want NTP and aren't interested in setting up PTP.
> 
> -- 
> Chris Caudle
> 
> 
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