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

    A server interface to the Portmapper, which establishes a mapping
    between the triple [prognum,versnum,protocol] and port on the
    server's Portmapper service. The svc_register routine calls this
    routine to register the server with the local Portmapper.