Line 30: EthernetClient ethClient; // instantiating the class Line 42 : client.setServer(server,1883); Connect to MQTT broker boolean connectionResult = client.connect("pjd-mqtt",MQTT_TOPIC,1,0,"Test Connection"); //arg1 - client id //arg2 - will topic //arg3 - will qos //arg4 - will retain //arg 5 - will message //api ref http://pubsubclient.knolleary.net/api.html