In the typical Web application, a client renders markup and the application or service is implemented as a set of tiered functions in the network. However, clients can contain resources useful for an application and network connections cannot always be assumed. In this paper, we consider extending the reach of a Web application to include: 1) access to and use of local client resources, and 2) operation while disconnected from the network. We, however, try to preserve desirable programming model and management characteristics of Web applications. We propose a system architecture and discuss an initial implementation using a portal as an example Web application.

Transcoding proxies are used as intermediaries between generic World Wide Web servers and a variety of client devices in order to adapt to the greatly varying bandwidths of different client communication links and to handle the heterogeneity of possibly small-screened client devices. Such transcoding proxies can adaptively adjust the amount by which a data stream is reduced, using an aggressive lossy compression method (e.g., an image becomes less clear, text is summarized). We present an analytical framework for determining whether to transcode and how much to transcode an image for the two cases of store-and-forward transcoding as well as streamed transcoding. These methods require prediction of transcoding delay, prediction of transcoded image size (in bytes), and estimation of network bandwidth. We discuss methods of adaptation based on fixed quality as well as fixed delay (automated/dynamic transcoding). We conclude with a description of the practical adaptation policies that have been implemented in our adaptive image transcoding proxy.