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ABC of ICT

Pete Roythorne gets to grips with how to use web-caching

As we increasingly use websites to enhance pupils' learning, the strain on schools' internet connections is becoming greater. In large schools, even a high-bandwidth* broadband connection may not be enough to stop your network wilting under the pressure of several classes all accessing websites at the same time. Try web-caching.

To understand how web-caching works you first need to understand a bit about websites themselves. Web pages are made of many different elements, such as text, pictures, graphics, illustrations and movies, each of which has to be downloaded to your computer for you to view the site properly, and this takes time. A web cache stores copies of all these elements on your school's network so that when you view the same page again all these elements can be accessed more quickly and so your school network runs much faster than the internet. This means regularly viewed websites can be accessed quickly and "bottlenecks" are prevented if you've got a whole class looking at the same website.

Some systems may also implement measures to preserve certain types of content at the discretion of the administrator. Also, some websites may come with their own caching instructions, in other words they will tell your server how to deal with the information on the site. For example, a frequently updated news page won't be cached at all, but other content can be cached indefinitely, or for a month or an hour. This ensures the user always receives up-to-date content that is the same as they would receive were they not using a cache.

What limits a cache is the amount of space available for it on your server (your main central computer). When your cache is full, older objects are removed and replaced with newer ones. So, for best results, caches should be at least 70Gb and should also be upgradeable.

Using a cache system can make a real difference to classroom use of the internet. By either visiting websites before a lesson with a computer that uses the cache or by pre-loading websites into the cache via a management system, you can have fast, high-quality access to websites without delays and without large numbers of students having to share an internet connection.

Although caching is not an alternative to increased bandwidth, what it does is optimises the usage of what's available.

*bandwidth = the amount of information that can be sent over a network connection in a given period of time.

Links www.avantisworld.com

getconnected.ngfl.gov.ukindex.php?s=info www.equiinet.co.uk

www.rm.com

www.squid-cache.org

www.web-caching.com

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