Differentiated multimedia Web services using quality aware transcoding

The ability of a Web service to provide low-latency access to its contents is constrained by available network bandwidth. It is important for the service to manage available bandwidth wisely. While providing differentiated quality of service (QoS) is typically enforced through network mechanisms, in this paper we introduce a robust mechanism for managing network resources at the application level. We use transcoding to allow Web servers to customize the size of objects constituting a Web page, and hence the bandwidth consumed by that page, by dynamically varying the size of multimedia objects on a per-client basis. We leverage earlier work on characterizing quality versus size tradeoffs in transcoding JPEG images to dynamically determine the quality and size of the object to transmit. We evaluate the performance benefits of incorporating this information in a series of bandwidth management policies. We develop metrics to measure the performance of our system. We use realistic workloads and access scenarios to drive our system. The principal contribution of this work is the demonstration that it is possible to use informed transcoding techniques to provide differentiated service and to dynamically allocate available bandwidth among different client classes, while delivering a high degree of information content (quality factor) for all clients.