NTSTATUS
NtRequestPort(
      __in HANDLE PortHandle,
      __in PPORT_MESSAGE RequestMessage
  );

Routine Description:

    A client and server process send datagram messages using this procedure.

    The message pointed to by the RequestMessage parameter is placed in the
    message queue of the port connected to the communication port specified
    by the PortHandle parameter.  This service returns an error if PortHandle
    is invalid or if the MessageId field of the PortMessage structure is
    non-zero.

Arguments:

    PortHandle - Specifies the handle of the communication port to send
        the request message to.

    RequestMessage - Specifies a pointer to the request message.  The Type
        field of the message is set to LPC_DATAGRAM by the service.

Return Value:

    NTSTATUS - A status code that indicates whether or not the operation was
        successful.