If a programmer specifies a socket, it can be bound or unbound. A service may register its port number with the local port mapper service. A programmer at the client machine can discover the server port number by consulting the port mapper at the server workstation. If the nusers server crashed earlier, this routine erases any trace of the crash before restarting. Finally, the program number for nusers is associated with the nuser procedure.
Registration is performed at the program level, rather than the procedure level.
The nuser routine has two requirements, unlike the registerrpc routine which performs them automatically. This is a simple test for detecting whether a remote program is running. Second, the subroutine checks for invalid procedure numbers. A programmer using the callrpc routine has control over neither the RPC delivery mechanism nor the socket used to transport the data. However, the lowest layer of RPC allows the user to adjust these parameters.