VMS Help TCPIP Services, Programming Interfaces, RPC Client Routines, callrpc, Description  *Conan The Librarian (sorry for the slow response - running on an old VAX)

    Calls the remote procedure associated with prognum, versnum,
    and procnum on the host host. This routine performs the same
    functions as a set of calls to the clnt_create, clnt_call, and
    clnt_destroy routines. This routine returns RPC_SUCCESS if it
    succeeds, or the value of enum clnt_stat cast to an integer if it
    fails. The routine clnt_perrno is handy for translating a failure
    status into a message.

                                   NOTE
       Calling remote procedures with this routine uses UDP/IP as
       a transport; see clntudp_create for restrictions. You do
       not have control of timeouts or authentication using this
       routine. If you want to use the TCP transport, use the clnt_
       create or clnttcp_create routine.