1. A cache which uses differences to speed up retrievals rproxy stores hashed values of retrieved pages and when you next access the same page it computes the difference between the current page and the recently stored page. The rproxy extensions to HTTP allow the server to generate a hsync relative to the cached instance in a way that is completely general, and transparent to both the server and user agent. rproxy, and clients and servers which implement hsync, calculate a block-by-block signature of the file, by computing a checksum over consecutive extents of equal length, such as 1024 bytes. This checksum is then added into a header of the request and transmited as usual. To be useful, there should be at least two rproxy instances between the client and the server. Transfers between the proxies will be delta-encoded, while the browser and server will just see standard HTTP. For example, it is very useful to run on instance on each side of a modem link, so that data across the slow link will be delta-encoded. Further information is available at http://linuxcare.com.au/rproxy/ From Debian 3.0r0 APT