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Encyclopedia > Web cache

Web caching is the caching of web documents (e.g., HTML pages, images) in order to reduce bandwidth usage, server load, and perceived lag. A web cache stores copies of documents passing through it; subsequent requests may be satisfied from the cache if certain conditions are met. For other uses, see cache (disambiguation). ... WWWs historical logo designed by Robert Cailliau The World Wide Web (commonly shortened to the Web) is a system of interlinked, hypertext documents accessed via the Internet. ... Electronic document means any computer data (other than programs or system files) that are intended to be used in their computerized form, without being printed (although printing is usually possible). ... A webpage or web page is a page of the World Wide Web, usually in HTML/XHTML format (the file extensions are typically htm or html) and with hypertext links to enable navigation from one page or section to another. ... A digital image is a representation of a two-dimensional image as a finite set of digital values, called picture elements or pixels. ... Bandwidth is the difference between the upper and lower cutoff frequencies of, for example, a filter, a communication channel, or a signal spectrum, and is typically measured in hertz. ... The inside/front of a Dell PowerEdge web server The term Web server can mean one of two things: A computer program that is responsible for accepting HTTP requests from clients, which are known as Web browsers, and serving them HTTP responses along with optional data contents, which usually are... For other uses, see Lag (disambiguation). ...

Contents

Types of Web caches

Web caches can be deployed in a variety of ways. User agent caches, such as those in web browsers, are private caches, operating on behalf of a single user. Intermediaries can also implement shared caches that serve more than one person. A user agent is the client application used with a particular network protocol; the phrase is most commonly used in reference to those which access the World Wide Web. ... An example of a Web browser (Mozilla Firefox) A web browser is a software application that enables a user to display and interact with text, images, videos, music and other information typically located on a Web page at a website on the World Wide Web or a local area network. ...


Proxy caches, also known as forward proxy caches, are usually deployed by internet service providers, schools and corporations to save bandwidth. Interception proxy caches (sometimes called "transparent caches") are a variant that doesn't require clients to be explicitly configured to use them. In computer networks, a proxy server is a server (a computer system or an application program) which services the requests of its clients by forwarding requests to other servers. ... “ISP” redirects here. ...


Gateway caches, sometimes known as reverse proxy caches, surrogate caches, or web accelerators, operate on behalf of the origin server, and to clients are indistinguisable from it. A number of gateway caches can work together to implement a Content Delivery Network. In telecommunications, the term gateway has the following meanings: In a communications network, a network node equipped for interfacing with another network that uses different protocols. ... A reverse proxy is a proxy server that is installed within the neighborhood of one or more servers. ... A web accelerator is a proxy server that reduces web site access times. ... In telecommunications, the term gateway has the following meanings: In a communications network, a network node equipped for interfacing with another network that uses different protocols. ... A content delivery network or content distribution networks (CDNs) is a system of computers networked together across the Internet that cooperate transparently to deliver content (especially large media content) to end users. ...


Intermediaries that cache often perform other duties, such as user authentication and content filtering. Multiple caches can also be coordinated using peering protocols like Internet Cache Protocol and HTCP. For other uses of the terms authentication, authentic and authenticity, see authenticity. ... DansGuardian blocking whitehouse. ... The Internet Cache Protocol (ICP) is a protocol used for coordinating web caches. ... The Hyper Text Caching Protocol (HTCP) is a protocol for querying, managing and discovering HTTP cache servers. ...


Controlling Web caches

HTTP defines three basic mechanisms for controlling caches: freshness, validation and invalidation. HTTP (for HyperText Transfer Protocol) is the primary method used to convey information on the World Wide Web. ...

  • Freshness allows a response to be used without re-checking it on the origin server, and can be controlled by both the server and the client. For example, the Expires response header gives a date when the document becomes stale, and the Cache-Control: max-age directive tells the cache how many seconds the response is fresh for.
  • Validation can be used to check whether a cached response is still good after it becomes stale. For example, if the response has a Last-Modified header, a cache can make a conditional request using the If-Modified-Since header to see if it has changed.
  • Invalidation is usually a side effect of another request that passes through the cache. For example, if URL associated with a cached response subsequently gets a POST, PUT or DELETE request, the cached response will be invalidated.

In 1998 the DMCA added rules to the United States Code (17 U.S.C. ยง 512) that largely relieves system operators from copyright liability for the purposes of caching. The Digital Millennium Copyright Act (DMCA) is a controversial United States copyright law which criminalizes production and dissemination of technology that can circumvent measures taken to protect copyright, not merely infringement of copyright itself, and heightens the penalties for copyright infringement on the Internet. ... The United States Code (U.S.C.) is a compilation and codification of the general and permanent federal law of the United States. ...


See also

purge means pig pg pg viginas In computer networks, a proxy server is a server (a computer system or an application program) which services the requests of its clients by forwarding requests to other servers. ...


References

  • Ari Luotonen, Web Proxy Servers (Prentice Hall, 1997) ISBN 0-13-680612-0
  • Duane Wessels, Web Caching (O'Reilly and Associates, 2001). ISBN 1-56592-536-X
  • Michael Rabinovich and Oliver Spatschak, Web Caching and Replication (Addison Wesley, 2001). ISBN 0-201-61570-3

External links


  Results from FactBites:
 
Web cache - Wikipedia, the free encyclopedia (346 words)
Web caching is the caching of web documents (HTML pages, images, etc.) in order to reduce bandwidth usage and web site access times.
Server-side caches, also known as reverse-caches and web accelerators, are placed in front of origin servers to reduce their load.
Web caches also perform related tasks such as user authentication and content filtering.
  More results at FactBites »

 
 

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