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

    Creates an RPC server handle using the UDP transport, to
    which it returns a pointer. Upon completion, xprt->xp_sock is
    the transport's socket descriptor, and xprt->xp_port is the
    transport's port number. The service is automatically registered
    as a transporter (thereby including its socket in svc_fds such
    that its socket descriptor is included in all RPC select system
    calls).