This is an integer, 0 to 255, identifying the specific running instance of the application, distinguished from fCAppID which identifies the application itself, that generated this notification on the FullCircle server. This matters when the same application runs multiple parallel instances, for example for load distribution across a busy trunk group, since this value is what lets a CDR collector tell those instances' records apart even though they share the same fCAppID. For example, two instances of a voicemail application running concurrently would each carry the same fCAppID but different values here, such as 1 and 2.