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What is a web cache? |
Do we need a web cache? | Who can use the web cache?
Configuring your web browser to use the cache | Frequently Asked Questions
Since the earliest days of the World Wide Web, web browsers have used caches (proxies/ proxy server) to store recently viewed images and web pages on disk. On subsequent visits to the web page, the browser looks to see if the pages have been modified since the last visit, and if they have not, the pages are instead retrieved from disk. This brings benefits to the user, in that the browser can rapidly display recently visited sites. It also reduces network traffic, and will significantly speed up access to popular web sites (e.g. search engines, Netscape's homepage, Microsoft's homepage, etc).
Although the local cache works well, it is very inefficient, in that it only caches documents requested by an individual user. It is far more sensible to have one cache for many users. The University has invested in two machines to act as a central web cache. This cache may be accessed by virtually all types of web browsers on a variety of operating systems. All that is required is a minor change to the configuration of the web browser.
"The available international bandwidth is increasing, but demand seems set to continue to outstrip supply. Networking, and particularly international connections, has come to consume more and more of the Universities' top-sliced budget for information systems and services, and it seems likely that a reckoning will have to come some time in the next few years." - The National JANET Web Cache Service. That was the situation some years ago. But now (2003) backbone network bandwidth within the UK academic community is plentiful, thanks to the introduction of the 2.5 Gigabits/second SuperJANET 4 network
From August 1998, charging was introduced for transatlantic network traffic using the JANET network during peak periods (0600 in the morning - 0100 at night). This only affected inbound traffic (e.g. Essex users viewing web sites based in the US).
The greatest percentage of inbound network traffic from the transatlantic link to the University of Essex is via the World Wide Web. Consequently, the most effective way of reducing our transatlantic traffic was to implement an effective web caching system.
But from 2001-2002 charging is no longer based on current transatlantic traffic, as JANET said in this announcement. Still, there are some reasons for having a web cache: for example, if the transatlantic link goes down on occasion many pages requested will be found in the cache. But the University of Essex web cache will eventually be taken out of service as there are disadvantages too - it can slow down access to web pages. The cache is no longer linked upstream to the JANET national cache (which has closed down).
The University has two machines to act as a local web cache. They have fast network connections and approximately 21 Gb of cache storage space each.
The web cache may be used by any member of the University, provided that their machines have an Essex IP address (i.e. begins with the digits 155.245). This is the case for machines connected to the university network, whether by being in the main campus buildings/student accommodation, or by using a dial-up modem connection to the university with the number 01206 792002. The machine you are reading this page with is not suitable for using the web cache.
Use of the web cache is currently optional, with two main exceptions. Firstly, all web traffic to the student accommodation (via the student gateway) is automatically routed via the web cache (so web cache settings do not need to be specified on these machines). Secondly, the web browsers provided in the Computing Service open access labs have been configured to use the cache. Other users are now recommended not to use the cache.
At the moment you are using the an unknown type of web browser. Instructions for configuring this web browser are here. Instructions for configuring a range of other browsers are accessible by using the drop-down list below:
Note that web browsers being used in the student accommodation network need to be configured using a different procedure.
If you have a web browser that is not listed above, or you are familiar with configuring web browsers, the cache is located at wwwcache.essex.ac.uk port 8080. The supported protocols are HTTP, HTTP-S, FTP and GOPHER. You should instruct the cache to bypass Essex web sites (i.e. those with the .essex.ac.uk suffix).
Some browsers (such as Netscape 3 and Netscape 4) support the use of automatic configuration scripts. If you are using a browser that supports such scripts, you are strongly advised to make use of this facility. The URL of the automatic configuration script is:
http://www2.essex.ac.uk/proxyconfig.pac
This URL is case sensitive, so take care.
If you use this script, you will not need to specify the location and port number of the web cache. Additionally, if the web cache becomes unavailable due to a network or hardware fault, your web browser will automatically route web traffic via a different web cache (or straight to the Internet). This script will also instruct your web browser to by-pass the cache for all UK academic sites (those with the .ac.uk suffix) and any other sites that have problems with caching.
Note that Internet Explorer 4 does not work with automatic configuration scripts.
The web cache Frequently Asked Questions have moved to this web page.
Try using European mirror sites. For example, Microsoft and Adobe maintain copies of their web pages in Europe.
Avoid downloading large files that are available on local networks or on CD-ROM. Popular programs such as Netscape Navigator, Internet Explorer 4.01 and the Adobe Acrobat reader are all available locally.