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Here you will find a wealth of resources about the subject of caching; an effective method of bandwidth management. Learn about what caching is and why it could be beneficial to your organisation, as well as information on some of the solutions available today.
The aim of this document is to clarify what caching is and what its advantages are. Please also refer to the "Caching solutions" section of the website where you will find details of caching hardware and software solutions, together with some guides for popular caching software.
In Worldwide Web terms, a cache is a place where temporary copies of web objects are kept. Normally when a user accesses the internet, web object requests go directly to the site of origin with the web object then being returned back to the user.
With a local cache in operation, user web object requests go via the local cache which then retains a copy of the said web object. This results in all subsequent requests for the same object being fulfilled from the local cache instead of from the site of origin. This process of web caching minimises the amount of times identical web objects are transferred from remote websites by retaining copies of requested URLs in a cache.
A web cache can be installed utilising both software and / or hardware, and can run on various different platforms. The BMAS website contains details of technical specifications and caching solutions which should provide a wide enough range of information to suit most budgets and areas of expertise.
With a local cache in operation subsequent requests for previously cached URLs result in the cached copy of the object being returned to the user; creating little or no extra network traffic, improving efficiency and reducing waiting time. This can be particularly effective when you consider the number of requests sent to the same popular websites.
Without a cache all your users requests go directly to the remote site generating web traffic and using up bandwidth.
There are many different solutions available to you if you need to set up your own local cache.
The purpose of this page is to provide you with an outline of what is required to create a local cache. For more detailed information about the majority of caching software packages available (listed by platform) and proprietary hardware available, please see the "Caching Solutions" section below.
We normally recommend that you use a machine specification similar to the one stated below together with software which will run on the operating system with which you are most familiar, especially if you are new to caching. Larger or smaller scale institutions may need to differ the specification.
Please see the "Technical Guides" section for configuration information for the most popular caching software, i.e.Squid (UNIX systems) and MS Proxy Server/Internet Security and Acceleration Server (Windows systems)
Hardware specifications -
700Mhz PIII CPU
6 x Ultra2 LVD SCSI cache disks
512 MB RAM
We recommend that you run your system on about 512MB RAM (certainly no less than 128) with the fastest
SCSI cache disks you can afford.
Operating systems
Caching software is available for the Apple Macintosh, Novell, Sun Solaris, most flavours of UNIX, and Windows operating systems. See "Caching Solutions" for more details.
Below we have listed all the main caching software solutions, sorted by platform. Many of these packages are actually web server packages with inherant caching facilities, although some, such as Squid, are dedicated caching packages.
The FULL Squid configuration guide is available on the Squid support website in HTML (compressed tar file) and PDF formats.
The full Squid Users guide can be found on the Squid website.
Below is a list of caching resources which should be useful. The list has links which cover all aspects of caching.
These days, most WWW browsers support proxy mode. This is the mechanism the browser uses to communicate with the cache server. Here is some detailed information about the setup for the known browsers.
Windows Browsers
Unix/X browsers
Mac browsers
Note that the names of the cache servers used in these examples are just that - examples. These should be replaced with the address of your site's cache server.
The Internet provides access to many different types of file - some of these do not lend themselves to being cached. In order to use a local cache effectively, there are some web objects that should not be cached - a list of these current types of objects is shown below.
Caching software can be easily configured to route directly to the URL of origin for web objects such as those described below.
Nb. There are also some URLs which do not allow caching for various reasons. A list of such sites can be made available in the form of an Access Control List for Squid users.
| WEB OBJECT | EXAMPLE | DESCRIPTION |
| Dynamically generated web objects | .php . asp | Web objects which are returned from the result of input into a database |
| SSL - a.k.a. https | Sites beginning "https" | Sites using Secure Socket Layer (SSL - aka https) normally bypass the cache. This is primarily for security reasons, as it is not recommended that sites containing personal data be cached. If an https site is goes through the cache, the user often sees an error message indicating that the server or dns cannot be found. |
| Real Audio and video | ||
| Sites that use IP authentication | Sites such as electronic journals etc | Requests have to go directly to the server of origin to enable authentication. If these sites were cached, your request would arrive via another machine resulting in the IP address being unidentified by the end server. |
| Local Sites or those within the academic domain | (.ac.uk) | Local and .ac.uk domain sites should not be cached to reduce latency to the request. Cost efficiency issues are not an issue with local sites. |
Any problems, comments or suggestions regarding this page, please e-mail the BMAS service manager bmas@ja.net
