Heartbeat information message returned when subscribing alarm/event, and it is in XML format.
<EventNotificationAlert version="2.0" xmlns="http://www.isapi.com/ver20/XMLSchema"> <ipAddress>10.17.133.46</ipAddress> <portNo>80</portNo> <protocol>HTTP</protocol> <macAddress>44:19:b6:6d:24:85</macAddress> <channelID>1</channelID> <dateTime>2017-05-04T11:20:02+08:00</dateTime> <activePostCount>0</activePostCount> <eventType>heartBeat</eventType> <eventState>active</eventState> <eventDescription>heartBeat</eventDescription> </EventNotificationAlert>