A monitor initiates a data collection by issuing a Start Performance Data Collection CNM RU. This signals VTAM® to begin gathering the specified performance data. While the data is being gathered, the monitor can issue Collect Performance Data CNM RUs to retrieve the data. When a request to collect data is issued, VTAM copies the performance data into a parameter list and invokes the monitor's performance monitor exit in VTAM's address space. The performance monitor exit then passes a copy of the parameter list to the monitor. The response to the Collect Performance Data CNM RU is not synchronized with the exit invocation. A Stop Performance Data Collection CNM RU should be issued when the monitor no longer requires the data to be gathered.