state : {
					/**
					 * operator metrics
					 */
					mutable CampaignMetricsType metrics = {};

					/**
					 * "empty" instances of data types used for initializations below 
					 */
					DayAggregateType dayAggregateEMPTY = {daySince1970=0u, callDurationPerDay=0u, droppedCallsPerDay=0u};
					SubscriberDataType subscriberDataEMPTY = {intervalDays = (list<DayAggregateType>) []};

					/**
					 * subscriber map to remember subscriber information in the interval
					 */
					mutable map<rstring, SubscriberDataType> subscriberMap;

					/**
					 * checkpoint file written when write cmd is received
					 * contains the serialized subscriberMap
					 */
					rstring checkpointFile=$checkpointFile;
					rstring metricsFile = checkpointFile+".meta";
				}