Typical RPC Call Scenario

When an application or a PC client calls a remote service, it needs to find the transport address of the service. In the case of TCP/UDP, the address is a port number. A typical procedure for this case is as follows:

1. The client sends the GETPORT message to the RPCBIND service on the remote machine. The GETPORT message contains the program number, and version and procedure number of the remote service it is attempting to call.
2. The RPCBIND service replies with a port number.
3. The client calls the remote service using the port number returned.
4. The remote service replies to the client.

A client also can use the CALLIT message to call the remote service directly, without determining the port number of the service. In this case, the procedure is as follows:

1. The client sends a CALLIT message to the RPCBIND service on the remote machine. The CALLIT message contains the program number, and the version and procedure number of the remote service it attempting to call.
2. RPCBIND calls the service for the client.
3. RCPBIND replies to the client if the call has been successful. The reply contains the call result and the services's port number.

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