@Override
        public void run() {
            logger.info("Starting EnquireLinkSender");
            while (isReadPdu()) {
                while (!sendingEnquireLink.compareAndSet(true, false) && isReadPdu()) {
                    synchronized (sendingEnquireLink) {
                        try {
                            sendingEnquireLink.wait(500);
                        } catch (InterruptedException e) {
                        }
                    }
                }
                if (!isReadPdu()) {
                    break;
                }
                try {
                    sendEnquireLink();
                } catch (ResponseTimeoutException e) {
                    close();
                } catch (InvalidResponseException e) {
                    // lets unbind gracefully
                    unbindAndClose();
                } catch (IOException e) {
                    close();
                }
            }
            logger.info("EnquireLinkSender stop");
        }