public Link(String name, double baudRate, double propDelay, int MTU)
                throws ParameterException, NullPointerException
    {
        super(name);
        String msg = name + "(): Error - ";
        if (baudRate <= 0) {
            throw new ParameterException(msg + "baud rate must be > 0.");
        }
        else if (propDelay <= 0) {
            throw new ParameterException(msg+"propagation delay must be > 0.");
        }
        else if (MTU <= 0) {
            throw new ParameterException(msg + "MTU must be > 0.");
        }

        this.baudRate_ = baudRate;
        this.delay_ = propDelay;
        this.MTU_ = MTU;
    }