Web Design & Development Guide

Push technology

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Push technology on the Internet refers to a style of communication protocol where the request for a given transaction originates with the publisher, or central server. It is contrasted with pull technology, where the request for the transmission of information originates with the receiver, or client.

Server push or webcasting is specifically related to the HTTP protocol, used on the World Wide Web. Typical World Wide Web usage is a pull operation - the end-user requests a web page using a web browser.

Push transactions are often based on information preferences expressed in advance - a "subscription" model. A home computer user might "subscribe" to various information "channels". Whenever new content was available on one of those channels, the server would "push" that information out to the user. Such transactions are common within digital marketing channels such as the following:

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.

E-mail is also a classic Internet push medium; UUCP and SMTP are push protocols. However, the last step - from a user's "home" mail server to his desktop - is typically a "pull" operation using a pull protocol like POP3 or IMAP. Modern e-mail clients make this last step appear to be a "push" operation by making repeated "pull" requests - for example, by checking for new mail on an IMAP server every ten minutes.

Most Web feeds, such as RSS, also 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.

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 (but not in Safari on the iPhone) 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.

The WHATWG is drafting a Web Applications 1.0 specification[1] which pushes content to the client. On September 1st, 2006, the Opera web browser implemented this new experimental technology in a feature called "Server-Sent Events."^[1][2]

Wireless Push Technology

The original BlackBerry was the first popular example of push technology in a wireless context^[3]. It automatically received short emails that were automatically sent to your device. Popular Wireless Push Technology has advanced since 1998, and has grown to include more complex information[4] All the new Windows Mobile (Windows Mobile 5 and 6) Versions use push technology to wirelessly send/receive emails, task and calender synchronization.

References

1. ^ Event Streaming to Web Browsers (2006-09-01).
2. ^ Opera takes the lead with AJAX support among browsers: More efficient streaming (2007-09-01).
3. ^ History of Push Technology March 2007
4. ^ Push Technology use example March 2007

External links

• W3C Push Workshop. A 1997 workshop that discussed Push technology and some early examples thereof.
• Netscape introduces server-push and client-pull in Netscape 1.1
• O'Reilly explains how to use Netscape server-push

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This guide is licensed under the GNU Free Documentation License. It uses material from the Wikipedia.