[ntp:questions] SNTP server + ntpd 4.2.4 client

Unruh unruh-spam at physics.ubc.ca
Tue Mar 18 18:05:46 UTC 2008

Noob <root at localhost> writes:

>Unruh wrote:

>> SNTP is a client protocol, not a server, according to RFC.

>You keep saying that. Which RFC are you referring to?

>> We have absolutely no idea what you are running on all your machines. You
>> never told us. This was an assumption based on the weird conditions you
>> stated. It really really helps if you give information when you ask for
>> help so that the help may actually be helpful. Tell us what your system is,
>> what "SNTP program" you are using as the server, what the other client
>> machines on the lan are running.

>The only client is an x86 PC running Linux (i.e. with 
>real-time extensions) and ntpd 4.2.4p0 at 1.1472.

>The server is an embedded device (HEOL-T101) with a GPS receiver and a 
>Fast Ethernet port. I have no idea what operating system runs on the 
>device; there might not even be an OS. The manufacturer claims the 
>device implements SNTPv4 instead of the full NTP.

Just looked it up. A bit bizarre-- power over the ethernet? The ethernet
has no power supply capability. Do you mean that you have to supply the
device with 60V running on one of the unused ethernet cable lines? Sounds
noisy to me. 

The GPS timing claimed is 40ns, but the timestamp is only 10usec. How much
does this thing cost? Are you really in a situation where this is a better
solution than say a cheap Garmin 18LVC?

>( http://www.heoldesign.com/index.php?id=58 )

>I plan to connect the two systems with a cross-over Ethernet cable.
>The round-trip time between the two systems would be 80-85 µs.

>> If you attach a GPS PPS receiver to one of your boxes (the server) and you
>> use a reasonable client then yes you can expect much better than 100 µs
>> accuracy on your net-- assuming it is not overloaded and the machines are
>> not overloaded with disk activity.

>The GPS receiver is inside the embedded device, which will serve time 
>over its Ethernet port.

>Considering the answers I've been given by you and by others in this 
>thread, I believe there is a good chance that the setup outlined above 
>will work.

YOu have not told us what the requirements are, so what "will work" is
is unclear. Yes, I am sure it will discipline your computer's clock.
probably to better than ms accuracy.

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