In this tutorial we've expanded on Tutorial 8 to provide a more discriminating server application. The changes to the clients were trivial, amounting to not much more than the addition of a timeout when reading a server's potential response. The server change was a bit more since it had to compare the clients' query with it's own signature.
In a "real" system, the signatures you swap would probably include version information. You could even use a major/minor scheme where an exact match isn't necessary. Another upgrade might be to have a set of signatures at one or both ends of the conversation. The level of service provided by the server would be determined by the signature pair match.
Here's the final file list: