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