- From: Roy T. Fielding <fielding@avron.ICS.UCI.EDU>
- Date: Tue, 06 Feb 1996 17:07:49 -0800
- To: Peter J Churchyard <pjc@trusted.com>
- Cc: http-caching@pa.dec.com
> Is anybody planning to do any modelling of these protocols? Yes, many people already have -- take a look at all four WWW conference proceedings. I am sure that more models will be made and analyzed in the future. > As I understand it, millions of http clients and servers may be > expected to implement a protocol thats designed to be used in a > continental mega cache - continental mega cache situation. Wouldn't this > rather special situation better be handled by a specific protocol for that > environment? No -- if any caching is possible, the choice of how and where the caches exist cannot be made by the protocol. Any client capable of making an HTTP request is also capable of retaining a cache. We already know that it is both possible and desirable for those caches to be layered. We also know that not all requests are cachable, and that finer control of caching options is desired for some resources. Therefore, what we need in the protocol is a way of expressing those options and the semantics of what is being expressed. Now, let's assume that there does exist a different protocol called MEGA. In that case, we have HTTP MEGA HTTP UA ----> Org Proxy ----> Regional Proxy ----> OS Given this configuration, what are the requirements on HTTP? The answer is: the same as they would be if MEGA=HTTP, since HTTP must be used to communicate the requirements from the origin to the User Agent no matter what exists in the middle. Note that in order to work, MEGA must be as flexible and extensible as HTTP and must also obey HTTP's requirements on intermediaries, which goes a long way toward explaining why people just use HTTP for this purpose. [BTW, for a long time now the initial application of HTTPng has been that of a MEGA protocol] The design requirement obtained from all this is that HTTP must be capable of supporting, or at least not preventing, multiple caching intermediaries along the request/response chain. This was not decided overnight -- I have been working on it for two years now. I already know it works (in fact, it even works without any of the improvements we have talked about here, provided that the user has a working Reload button). It will work even better once we have a good written description for cache-control. ...Roy T. Fielding Department of Information & Computer Science (fielding@ics.uci.edu) University of California, Irvine, CA 92717-3425 fax:+1(714)824-4056 http://www.ics.uci.edu/~fielding/
Received on Wednesday, 7 February 1996 01:31:10 UTC