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Tip of the Month

Network Analysis Tip of the Month – August 2006

Apdex: Application Performance in a Nutshell

By Jeff Trawick, WildPackets Professional Services

Network analysts are often flooded with a vast array of statistics, second only to the sometimes infinite statistics of baseball (The only times he has batted 3-for-4 was on Tuesdays in odd-numbered months when it was raining…). No, getting statistical data about our networks is usually not the problem. An almost endless variety of network management tools can provide more numbers than we can logically devour. So how do we make sense of it all? How can we get a better and more practical view of how the network is really functioning for users? How does the current performance of a given application affect the experience of users and their productivity? Enter Apdex - one of the newest and coolest features in WildPackets’ analysis products. Apdex is short for Application Performance Index, a metric based on calculations devised by the Apdex Alliance. Check out the Apdex website (http://www.apdex.org) for more detailed information.

The Peek analyzer collects samples of task times for each application, and classifies each sample as “satisfied,” “tolerating,” or “frustrated,” with respect to user experience. These categories are based on user-configurable time thresholds within the Peek Expert. The number samples in each of these three categories are fed into a formula to arrive at a single numerical value known as the Apdex Score. This score is always between 0 and 1. Scores can be assigned to individual sessions for an application or to an application as a whole. If an application or session receives a score of 1.00 (the highest possible score), then all users of that application should be satisfied. The lower the score, the less satisfied users will be. The following diagram illustrates the range of Apdex scores versus user satisfaction:

Apdex User Satisfaction Scores

Based on this scale, you should obviously aim to have your applications perform so that their Apdex scores are 0.85 or more. The idea is to obtain the highest scores for your most mission-critical applications and user groups. If users are in the tolerating range or have fallen into the frustrated range, business productivity will suffer as the users become distracted from their primary tasks.

Take a look at this example from the Peek analyzer’s Expert Applications view. The Peek Expert shows the Apdex score calculated for each application and the number of samples used for the calculations.

Click on thumbnail for larger view

To put Apdex in a practical context, consider an organization that relies heavily on web-based applications. The Apdex score for the Web apps in this capture session tells us that performance for web applications is excellent. On the other hand, if the organization depended on Citrix or CIFS, then productivity would probably be less than optimal since the Apdex scores for these applications indicate that most user are frustrated.

The goal is to identify and prioritize the applications in your organization that are mission-critical. Then, use the Peek analyzer to determine the Apdex score for each application. Ideally, you want your most crucial applications to have the highest Apdex scores. This is known as aligning application performance with business priorities – a process that makes real sense for your organization. If less important applications are performing better than the more vital apps, then you’ll probably want to consider modifications in your IT environment that will allow the prioritized apps to enjoy the best possible performance levels. That’s where your Peek analyzer can excel: the Peek Expert’s Apdex reporting can help you visualize current performance and make adjustments to achieve optimal performance in your network. Give it try!