Trial access to the University of Cambridge WWW cache server


NOTE: Only systems within the University of Cambridge (hostnames ending cam.ac.uk) have access to the cache server. Systems outside the cam.ac.uk domain are not authorised to use the cache.

Table of Contents

Please read the whole of this document, not just the WWW client configuration notes! If you decide to try using the cache server, please send any problem reports or comments to webmaster@ucs.cam.ac.uk.

Announcements and other information relating to the WWW cache trial will be made available through the local ucam.comp.www.misc newsgroup and the cache status and news summary.

Introduction

An article in the Computing Service newsletter no. 186 (April 1996) described the purpose of a WWW proxy/cache server, and mentioned that the Computing Service intended to set up a WWW cache server on a pilot trial basis.

See that article for more detailed background information. In summary, though, if a WWW client ("browser") is configured to use a WWW proxy/cache server ("cache server"), it will pass some (or all) requests for documents to the proxy server instead of connecting direct to the server which holds the master copy of the document. The proxy/cache server may then act as intermediary ("proxy") and pass on the request, or it may instead send to the client a copy of the document which it has saved ("cached") following an earlier request for the same document.

The server takes care to ensure that documents supplied from the cache are "recent" (see below for further details), though changes to the master copies may not be noticed immediately. Documents which cannot be cached usefully or safely (e.g. search results, output from forms, etc.) will not be retained in the cache.

Overall, this should result in documents being received faster on average, and reduce the volume of WWW traffic over busy international network links. Since international network capacity to and from JANET (the UK academic network) is often overloaded, there is strong pressure for all JANET sites to use WWW cache servers.

Aims of the Pilot Trial

The aims of the pilot trial are While we would like as many people as possible using the cache (not least since its effectiveness as a cache will be poor if usage is low), users during the pilot trial should be willing to use the cache whenever possible, but know how to disable use of the cache temporarily (connecting direct to the target servers instead) if there are problems with the cache server (or with the national HENSA cache, to which the local server may pass requests for documents that are not available from the local cache).

In consequence, the pilot trial is aimed at individuals, and we would not recommend configuring software on departmental or college systems to use the cache automatically for all users, potentially leaving them frustrated if there are problems with the cache, not realising they could bypass it or even that they are using it, and (for example) that announcements of cache server downtime affect them. Encouraging the more experienced or adventurous users of departmental or college systems to read this document and then try using the cache would be a much safer approach.

Anyone who decides to use the cache server is advised to watch for trial-related announcements on the ucam.comp.www.misc newsgroup. General news and information about the pilot trial, including details of cache server configuration changes, can be found in the cache status and news summary. Comments to webmaster@ucs.cam.ac.uk. are welcome on whether changes reported in either place seem to be beneficial, neutral, or detrimental in their effect.

Availability

The cache server is intended to be available at all times, subject to the usual exclusions such as hardware or software failure, disruption of network access (whether scheduled or otherwise), and necessary downtime for software or hardware maintenance. Problems arising outside working hours may not be noticed or rectified before the next working day.

Scheduled downtime (for the WWW cache server in particular, or other services which may affect it or access to it) will be announced in the same ways as for other Computing Service systems, as will details of any extensive unscheduled downtime.

One exception, during the pilot trial, is that in order to deal quickly with any problems that come to light, system restarts may not be announced in advance in the same way as for other Computing Service systems (and hence possibly delayed). Where urgent, such restarts may be done at any time; otherwise, they will be restricted to the advertised "vulnerable periods" during which maintenance activities for Computing Service systems are normally scheduled. System restarts should normally cause only a 2-3 minute interruption to service. See netnews for details of the standard "vulnerable periods" and announcements of scheduled downtime.

Warnings and Limitations

To give some idea of what to expect if you use the cache server during the trial:

Configuring WWW clients (browsers)

Quick start summary

If you are familiar with your WWW client's configuration facilities, this summary may be sufficient to get started.

Detailed instructions

[under construction]

The following documents provide information about configuring various widely-used WWW clients (browsers). If the one you are using is not covered, you will need to work out how to configure it using the information in the "quick start" section above in conjunction with the client program's own documentation or "help" information.


Documentation for other browsers is in preparation, but has been delayed.

For now, the documentation for the Manchester Computing (University of Manchester & UMIST) cache server may provide sufficient guidance BUT you MUST use the address details for the University of Cambridge cache server instead of the addresses shown in Manchester's examples (i.e. "wwwcache.cam.ac.uk" and "8080" should be specified, in a format appropriate to the browser). Read the following notes before following the link to Manchester's documentation!

The differences between Manchester and Cambridge configurations are:

Manchester Computing's documentatation about their cache server and how to configure web browsers to use the cache can be found at http://www.mcc.ac.uk/Cache/.

Technical notes

Cache server configuration

The pilot trial is using a Sun SPARCstation 20/151 system running Solaris 2.5, with 128MB memory and 8GB of disc, and using the Netscape Proxy Server V1.12.
webmaster@ucs.cam.ac.uk; last updated 9 May 1997