[ntpwg] Testing NTP performance

[STUART VENTERS]

>>Not to get too philosophical, but isn't this a description of the  
>>precise problem that NTP itself is designed to solve?

>>Rob Seaman
>>NOAO
>>--


Rob,

Guilty as charged, there is circular logic here.
   I'm using NTP's ability to transport time to measure same.

But perhaps I can get out on a technicality.
   I'm proposing to use the time transport ability over easy links
       to measure the time transport ability over a more difficult link.

I'd be happy to say that the only unit under test is A
  and so B and C can be 'Golden units'.

I need to test down to sub-millisecond accuracy.
  There are servers available for B with 100nS accuracy.
  There are packet bert testers that could pinch hit as a client C with similar accuracy.
  These should be sufficient to get us to uS accuracy.

Again, this seems like a complicated plan, there ought to be an easier way.

Asked another way, folks here have claimed that NTP runs
 with particular accuracies much tighter
   than a human can check by printing out the time on a console.

How do they know?


Regards,

Stuart





> Greetings,
>
> I'm puzzling over how to test embedded NTP implementations.
>
> Given a client and server connected through some test network,
>   how do you accurately measure the difference between the server  
> and client clocks.
>
> If there was a 1PPS test wire coming out of each implementation, it  
> would be easy.
>   But unless you can add code to the client, there is usually not a  
> wire,
>
> I need some way to peek into the client and server to see their  
> internal clocks.
>
> I'm thinking the server functionality embedded with the client might  
> help.
>
>
> Consider the following system with a third NTP box:
>
>
>                        (C)
>                       CLIENT
>                    /         \
>                  /             \
>                /                 \
>              /                     \
>            /                         \
>          /
>      SERVER ---------- TEST  ------ CLIENT/SERVER
>        (B)            NETWORK           (A)
>
>
>
> We are trying to measure the effects of the test network on the  
> client in A.
>
> Server B provides a stable timing reference for the test.
>
> Client/Server A is locked to Server B through the test network.
>
> Client C is connected to servers A and B.
>
>
> If the links connecting Client C are simple point to point links,
> then hopefully most of the errors in time transport
>   are due to the test network affecting A.
>
> C provides an offset between B&C and also between A&C.
>
> It seems like the difference between these offsets
>  should be the offset between A&B.
>
> This seems like a complicated plan, is there a better way?
>
>
> Regards,
>
> Stuart
>
>
> ps: My apologies for an NTP 101 question.
>     Perhaps someone could point me to where this has already been  
> sorted out.