Network Path and Applications Diagnosis (NPAD)

	On a short path between a server (S) and a local client (LC), the Transmission Control Protocol TCP can hide and compensate for application flaws. Across a wide area network, however, the path delay between the server and a remote client (RC) will expose the underlying flaws.

A key piece missing from networking's end-to-end performance puzzle is that the current set of diagnostic strategies do not adequately account for the effects of network path delay. The NPAD project team is developing extensions to existing diagnostic tools that will effectively take path delay into consideration, compensate for a variety of delay times, and test the effects of these new diagnostic tools with network users and operators, using actual high-performance applications. Due to recent insights gained from the past Web100 and Net100 projects, we can show that the missing piece of the performance diagnostic puzzle is that the symptoms of most application and network defects scale with increasing path delay. For example, a minor defect in a campus LAN might have an insignificant or negligible effect on an application running on a 1-ms path across campus. However, that same defect has a greater impact on performance when running on a long path across the continent.

The NPAD diagnostic server, Pathdiag, is designed to easily and accurately diagnose problems in the last-mile network and end-systems that are the most common causes of all severe performance degradation over long end-to-end paths. Our goal is to make the test procedures easy enough and the report it generates clear enough to be suitable for end-users who are not networking experts. In most situations, a single test run, launched from a web page, will generate a report that enumerates all problems affecting downloading (fetching) of data from a remote site. Although the report contains extensive explanations of the results, we do not assume that end-users will be able to correct network problems themselves. The reports include guidance to help end-users properly engage a system or network administrator and supply the necessary information to help the administrator locate the problem.

Testing is beginning to expose otherwise hidden flaws and impediments that contribute to delay. The NPAD software tools are currently being used and tested at PSC, NCAR, Internet2, ONEnet, LBNL, and Duke University.

These investigations into the fundamental operation of networks support NCAR's strategic goal of "Providing robust, accessible, and innovative information services and tools." Network Path and Application Diagnosis is a joint project of the Pittsburgh Supercomputing Center and NCAR, funded under NSF grant ANI-0334061. This project is focused on using Web100 and other methods to extend fairly standard diagnostic techniques to compensate for the "symptom scaling" that leads to false positive diagnostic results on short paths.