[ntpwg] Testing NTP performance

[STUART VENTERS]

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.