Push technology

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Push technology, also called server push or webcasting, describes an Internet-based content delivery system where information is delivered from a central server to a client computer based upon a predefined set of request parameters outlined by the client computer. A client computer such as a desktop home user would subscribe to various information topics provided by a content provider and as that content is created by the content provider, such information is "pushed" or delivered across the Internet to the desktop home user and displayed on that user's computer. Push Technology differs from normal World Wide Web usage, where a user has to request a Web Site through a web browser.

E-mail is the classic Internet push media; however, this depends on the configuration used. If the messages are stored on a server and not automatically pushed to the client, then it is not technically push media. Instant messaging epitomizes push media. Messages and files are pushed to the user as soon as they are sent to the messaging service. Some peer-to-peer programs, such as WASTE, also allow pushing files. In these cases, the sender initiates the transfer rather than the recipient.

Most Web feeds, such as RSS, appear to be push media, but technically are pulled by the user. With RSS, the user's aggregator polls the server periodically for new content; the server does not send information to the client unrequested. This continual polling is inefficient and has contributed to the shutdown or reduction of several popular RSS feeds that could not handle the bandwidth. In contrast, a "true" RSS-like push media would report new syndication items to each subscriber as soon as they were updated and would not require polling. However, "true" push media presents practical difficulties because the server is responsible for remembering who the subscribers are, and for remembering the latest address that each subscriber should be contacted at.

Another type of Push technology gained popularity in the 1990s using PointCast software. It received considerable media attention, and both Netscape and Microsoft integrated it heavily into their software at the height of the browser wars. However, most people did not find push technology useful, and it later faded into more obscure corners of software packages.

[edit] HTTP Server Push

The term server push was originally coined by Netscape in 1995. A special content type was added to HTTP called multipart/x-mixed-replace which the Netscape 1.1 and subsequent browsers would interpret as a document changing whenever the server felt like pushing a new version to the client. It is still supported by Mozilla, Firefox, Safari and Opera today, but traditionally ignored by Microsoft. It can be applied to HTML documents, making it quite popular for webchats, but also for streaming images in webcam applications. The Comet technique tries to emulate server-push with a lot of overhead in Javascript programming.