6.3 Aborted Pages and QoS

User-perceived QoS is another important metric to consider in EtE monitor. One way to measure the QoS of a web service is to measure the frequency of aborted connections. However, such simplistic interpretation of aborted connections and web server QoS has several drawbacks. First, a client can interrupt HTTP transactions by clicking the browser's ``stop'' or ``reload'' button while a web page is downloading, or clicking a displayed link before the page is completely downloaded. Thus, only a subset of aborted connections are relevant to poor web site QoS or poor networking conditions, while other aborted connections are caused by client-specific browsing patterns. On the other hand, a web page can be retrieved through multiple connections. A client's browser-level interruption can cause all the currently open connections to be aborted. Thus, the number of aborted page accesses more accurately reflects client satisfaction than the number of aborted connections.

For aborted pages, we distinguish the subset of pages $\Pi_{bad}$ with the response time higher than the given threshold X_EtE (in our case, X_EtE=6 sec). Only these pages might be reflective of the bad quality downloads. While a simple deterministic cut off point cannot truly capture a particular client's expectation for site performance, the current industrial ad hoc quality goal is to deliver pages within 6 sec [12]. We thus attribute aborted pages that have not crossed the 6 sec threshold to individual client browsing patterns. The next step is to distinguish the reasons leading to poor response time: whether it is due to network or server-related performance problems, or both.