The commonly agreed Zipf-like access pattern of Web workloads is mainly based on Internet measurements when text-based content dominated the Web traffic. However, with dramatic increase of media traffic on the Internet, the inconsistency between the access patterns of media objects and the Zipf model has been observed in a number of studies. An insightful understanding of media access patterns is essential to guide Internet system design and management, including resource provisioning and performance optimizations.

We have studied a large variety of media workloads collected from both client and server sides in different media systems with different delivery methods. Through extensive analysis and modeling, we find: (1) the object reference ranks of all these workloads follow the stretched exponential (SE) distribution despite their different media systems and delivery methods; (2) one parameter of this distribution well characterizes the media file sizes, the other well characterizes the aging of media accesses; (3) some biased measurements may lead to Zipf-like observations on media access patterns; and (4) the deviation of media access pattern from the Zipf model in these workloads increases along with the workload duration.

We have further analyzed the effectiveness of media caching with a mathematical model. Compared with Web caching under the Zipf model, media caching under the SE model is far less effective unless the cache size is enormously large. This indicates that many previous studies based on a Zipf-like assumption have potentially overestimated the media caching benefit, while an effective media caching system must be able to scale its storage size to accommodate the increase of media content over a long time. Our study provides an analytical basis for applying a P2P model rather than a client-server model to build large scale Internet media delivery systems.

The Speaker:
Xiaodong Zhang is the Robert M. Critchfield Professor in Engineering, and Chairman of the Department of Computer Science and Engineering at the Ohio State University.

His research interests cover a wide spectrum in the areas of high performance, distributed and networking systems. Several technical innovations and research results from his team have been widely adopted in commercial processors and major operating systems and database systems, making direct contributions to the advancement of computer memory systems. Recently, their open source software TopBT (a topology-aware BitTorrent client) has been frequently used by P2P users worldwide, which eliminates unnecessary network traffic and keeps a high downloading speed.

Xiaodong Zhang received his Ph.D. in Computer Science from University of Colorado at Boulder, and B.S. in electrical engineering from Beijing University of Technology. He is a Fellow of the IEEE.

* ALL ARE WELCOME
Contact : Prof. George Baciu
Email : csgeorge@comp.polyu.edu.hk
Tel : 2766-7295 or 2766-7272