Two models run in a client-server, remote procedure call (RPC) communication pattern. The client model `client` sends requests and receives response to/from the server model `server` via the deprecated `call` method. The server model receives requests and send responses. This example demostrates the RPC pattern through the use of the `client_of` and `is_server` model parameters and the RPC interface classes/functions. The `client` model also sends request/response pairs to a file.
