Calls per Minutes is described by the average number of incoming or outgoing calls per minute during the specified time from the node to their destination.
A call, as represented by the calls per minute metric, can represent a somewhat different type of event depending on whether it is counted in the context of the application or tier. At the application level (i.e., Overall Application Performance), a call corresponds to a business transaction invocation. At the tier level, a call corresponds to individual invocations of services on that tier. Thus the number of calls per minute at a particular tier can exceed the number of calls per minute that is shown for the same time period at the application level, since a single execution of a business transaction can involve multiple calls to a single tier.