[ntpwg] Testing NTP performance

[Rob Seaman]

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
--

On May 1, 2008, at 12:47 PM, STUART VENTERS wrote:

> 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.
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