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

 addr
    A pointer to a sockaddr_in structure containing the internet
    address of the host where the remote Portmapper resides.
 prognum
    The program number associated with the remote procedure.
 versnum
    The version number associated with the remote procedure.
 protocol
    The transport protocol that the remote procedure uses. Specify
    either IPPROTO_UDP or IPPROTO_TCP.