1. A method, comprising: identifying service impact events in an alarm dataset from a cloud software defined network, the service impact events including service alarms; identifying alarm sources associated with the service impact events; identifying impacted network service alarms provided in the cloud software defined network according to the alarm sources; identifying service alarm type classifications for the impacted network service alarms; by a processor of a service impact event analyzer, identifying a service impact model comprising the service alarm type classifications and the service impact events, the model describing impacts of the service impact events on network services; using the service impact model, identifying association rules of parent and child event relationships of the service impact events, so that parent events are primary events for root causes of trouble, and child events are correlated to parent events; by the processor, computing time durations of the service impact events using correlated secondary alarms, the correlated secondary alarms being identified using the service impact model; and by the processor, evaluating a risk area and degree of service assurance based on the time duration and on the service alarm type classifications.