For example, Application Protocol Response probes look at the application protocol to measure application transaction times. As with any probe-based solution, certain transactions cannot be measured accurately. However, given the nature of this measurement, it is likely to be a close sample of what the user sees for high-level transactions. Probe placement is also critical to the success of this methodology, but the jury is still out on whether measuring ACK response correlates well with what the user sees. The downside is that the software needs to be installed on every end-user system and could be cumbersome to manage.
Test drive The accuracy of tools used to measure response time is easy to determine.
Test the tool on the actual application you are trying to measure and publish the numbers to end users for a month. If end users agree that response time goes up when there is not much traffic and goes down when traffic increases, then the tool is accurately measuring what users see. Because today's response time tools are new, their ability to provide good service is still not well understood. It is too early to tell if they are effective measuring devices for the complex application scenarios deployed today. Ultimately, their success or failure will depend on their ability to reflect in objective metrics what users know and feel subjectively.