[ntp:questions] Re: Hardware SNTP server

Terje Mathisen terje.mathisen at hda.hydro.com
Thu Sep 8 06:19:57 UTC 2005


Hiroshi Toriyama wrote:

> Hi,
> 
> We are planning to operate public stratum 1 servers.
> Because we don't want to deal with the server overload,

That (overloading the server, not the network) is actually quite hard to
do! :-)

> we developed a high-throughput SNTP server using FPGA.

Hmmm.
> 
> This server can respond up to the wire speed of GbE and
> the timestamp jitter is within 8 nano-seconds.

Wow!

> Though the performance seems sufficient, we afraid there
> can be potential problems because complex functions
> are omitted in this server.
> It responds only to NTP request pakets in unicast UDP,
> it can't handle authentication options, KoD, etc...

This is still fine for a public S1 server:

- You don't need KoD because you'll never be processing-limited.
- You don't need to support authentication unless you have to serve
clients (i.e. paying customers) who absolutely require crypto-traceable
timestamps.
- Broadcast/manycast isn't needed or really possible for a public S1 server.

> 
> Can anyone point out whether such server is suitable
> for a public stratum 1 server?

I do wonder what your reference clock is? The entire ensemble of
japanese UTC atomic references? How do you transfer that time into the
server timebase?

I assume you have built these clocks with some kind of hw counter that's
directly coupled to the output osc of an atomic clock, with external
inputs to initialize it, define the correspondence between counter value
and UTC/TAI time etc?
> 
> Any comments would be appreciated.
> 
> Experimental servers can be accessed at;
> sntp1.nict.go.jp
>     IPv4: 133.243.230.51
>     IPv6: 2001:e38:2020::123
> sntp2.nict.go.jp
>     IPv4: 133.243.230.52
>     IPv6: 2001:e38:2020::124
> Clock source: 1PPS and 10MHz from UTC(NICT)

I just added these two to my deskside Oncore-based S1 server, besides
the 264 ms RTT, everything seems very nice.

For sntp1 with a PPS input you must have a stabilized local frequency
source to allow interpolation between pulses at the required ns level,
sntp2 could get away with simply counting the 10 Mhz reference ticks,
but I assume it still has a similarly stable local timebase?

I'm impressed! :-)

Terje
> 
> Hiroshi Toriyama
> Time Applications Group
> NICT, Japan


-- 
- <Terje.Mathisen at hda.hydro.com>
"almost all programming can be viewed as an exercise in caching"




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