private static final int DEFAULT_WITNESS_PORT = 135;  // RPC endpoint mapper
    
    public interface WitnessNotificationListener {
        void onWitnessNotification(WitnessNotification notification);
        void onRegistrationFailed(WitnessRegistration registration, Exception error);
        void onRegistrationExpired(WitnessRegistration registration);
    }
    

    public interface WitnessNotificationListener {
        /**
         * Called when a witness notification is received.
         *
         * @param notification the witness notification
         */
        void onWitnessNotification(WitnessNotification notification);

        /**
         * Called when a witness registration fails.
         *
         * @param registration the failed registration
         * @param error the error that occurred

    }

    /**
     * Handle witness notifications
     */
    private class WitnessNotificationHandler implements WitnessClient.WitnessNotificationListener {
        @Override
        public void onWitnessNotification(WitnessNotification notification) {
            handleWitnessEvent(notification);
        }

        @Override
        public void onRegistrationFailed(WitnessRegistration registration, Exception error) {