[geeks] DiY Stratum 1 server

[Alois Hammer]

On Mon, 17 Mar 2008 18:51:25 -0400, "Sridhar Ayengar"
<ploopster at gmail.com> said:
>
> If you're talking stratum-1, you're going to want timescales shorter 
> than that.  You can easily achieve those sorts of precision with
> a stratum-2 on a decent connection with low latency against decent
> stratum-1s.

@home project, so of course the latency is variable and resistant to
measurement (business cableco ISP, but still cableco).  That's why I'd
like to have the stratum 1 device on the local network. :)

> I wonder how big of a difference there is in performance between GPS and
> CDMA?  I've observed a significant price difference, probably because 
> CDMA signal is so much easier to receive.

My information is that CDMA uses GPS receivers on the tower to provide
clocking.  I don't know a lot about CDMA as a layer one network
protocol, but I'm guessing that putting CDMA in between you and the GPS
receiver noticeably reduces the accuracy.  Probably at least as much as
having a GPS <-> Bluetooth <-> USB <-> PC setup.

Which leads to an interesting question: can/does ntpd find and reject
clock sources that can't provide sufficiently low-latency responses, or
does it blindly treat external clocking sources as authoritative because
you told it they were?

> I wouldn't trust either RS-232 or USB, myself.  There are reasonably 
> priced devices with synchronous interfaces, if you look.

I'm not sure what a synchronous interface is in this context, at least
in the context of "thing I would plug into a PC."