How to identify the RFC callers?

We have a R/3 version 4.0b system that we wish to retire.

There are few RFCs existing in the system. We wish to identify the other systems that are consuming these RFCs.

So we can inform them to switch to the new system.

Please provide some tips:

     How to identify the name (IP address) of other systems which are consuming a RFC?

          I only have the name of the RFC and access to the R/3 system.

thanks,

Madan