Content Adaptation and Negotiation

Transcoding proxies are used as intermediaries between generic World-Wide-Web (WWW) 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, etc.)

The Mobile Networking Group has designed and implemented an image transcoding proxy, which improves the response time of wireless Web surfing by aggressively compressing images. In addition, our group has written a paper that develops 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 the estimation of network bandwidth. We have explored methods of adaptation based on fixed quality as well as fixed delay (automated/dynamic transcoding). A number of practical adaptation policies have been implemented and successfully demonstrated in our adaptive image transcoding proxy.

We have designed and implemented image transcoding within an HTTP proxy. Our proxy also permits limited text transcoding and summarization. The end user can adjust the amount of compression via a slide bar. The internal architecture of the transcoding proxy-based system is outlined in the figure.

Papers and Slides

Dynamic Adaptation In an Image Transcoding Proxy For Mobile Web Browsing, IEEE Personal Communications Magazine, December 1998.