Re: Hardware SNTP server

Following article has been lost because of our
server trouble.
I'm sorry it became so slow reply.

Hiroshi Toriyama

--------------------------
Terje Mathisen wrote:

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

Our hardware has two GbE port and can be used as a
"passing through mode."
Directly connecting our SNTP server and passing through
time stamper, packet delay graph shows a horizontal line,
or two horizontal lines different by 8 nano-second.

> 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.

Thank you for your comment.

> 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?

Because UTC(NICT) is generated in the same building,
we can feed 1PPS and 10MHz signal only with a multi-port amplifier
and coaxial cables.

We also have a remote experiment site, where we use a cesium clock
and GPS common view equipments.

> 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?

Yes,
internal PLL generates 250MHz from external 10MHz, and
the fraction of a timestamp is culculated from this 250MHz count.
The integer part is just a PPS count plus offset.
Incoming NTP packet is processed in a hardware pipeline, and
just 832ns after, the NTP response is sent from the same GbE port.
Most of these functions are implemented in a FPGA.
http://www2.nict.go.jp/dk/c272/index-e.html

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

Thanks.
But please be careful with some values in response NTP message.
Precision, Root delay, and Root dispersion are constant values
set in FPGA registers beforehand.

> 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?

sntp2 uses UTC(NICT) directly.
sntp1 uses a rubidium clock which is locked to UTC(NICT).
The firmware version of sntp1 is slightly older.

Hiroshi Toriyama
Time Applications Group
NICT, Japan
.

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