Pull coding or client pull is a style of

network Network, networking and networked may refer to: Science and technology * Network theory, the study of graphs as a representation of relations between discrete objects * Network science, an academic field that studies complex networks Mathematics ...

communication where the initial request for data originates from the

client Client(s) or The Client may refer to: * Client (business) * Client (computing), hardware or software that accesses a remote service on another computer * Customer or client, a recipient of goods or services in return for monetary or other valuabl ...

, and then is responded to by the server. The reverse is known as

push technology Push technology or server push is a style of Internet-based communication where the request for a given transaction is initiated by the publisher or central server. It is contrasted with pull/get, where the request for the transmission of informa ...

, where the server ''pushes'' data to clients. Pull requests form the foundation of network computing, where many clients request data from centralized servers. Pull is used extensively on the

Internet The Internet (or internet) is the global system of interconnected computer networks that uses the Internet protocol suite (TCP/IP) to communicate between networks and devices. It is a '' network of networks'' that consists of private, pub ...

for

HTTP The Hypertext Transfer Protocol (HTTP) is an application layer protocol in the Internet protocol suite model for distributed, collaborative, hypermedia information systems. HTTP is the foundation of data communication for the World Wide We ...

page requests from

website A website (also written as a web site) is a collection of web pages and related content that is identified by a common domain name and published on at least one web server. Examples of notable websites are Google, Facebook, Amazon, and Wi ...

s. A ''push'' can also be simulated using multiple ''pulls'' within a short amount of time. For example, when pulling

POP3 In computing, the Post Office Protocol (POP) is an application-layer Internet standard protocol used by e-mail clients to retrieve e-mail from a mail server. POP version 3 (POP3) is the version in common use, and along with IMAP the most common ...

email messages from a server, a client can make regular pull requests every few minutes. To the user, the email then appears to be pushed, as emails appear to arrive close to real-time. The tradeoff is this places a heavier load on both the server and network to function correctly. Most

web feeds On the World Wide Web, a web feed (or news feed) is a data format used for providing users with frequently updated content. Content distributors ''syndicate'' a web feed, thereby allowing users to ''subscribe'' a channel to it by adding the feed ...

, such as RSS are technically pulled by the client. With RSS, the user's

RSS reader In computing, a news aggregator, also termed a feed aggregator, feed reader, news reader, RSS reader or simply an aggregator, is client software or a web application that aggregates syndicated web content such as online newspapers, blogs, pod ...

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.Sia, K. C., Cho, J., and Cho, H. K.,
Efficient Monitoring Algorithm for Fast News Alerts, 2007
IEEE TKDE, Vol. 19, Issue 7, pp. 950-961 For solving this problem, the

WebSub WebSub (formerly PubSubHubbub) is an open protocol for distributed publish–subscribe communication on the Internet. Initially designed to extend the Atom (and RSS) protocols for data feeds, the protocol can be applied to any data type (e.g. ...

protocol as another example of a push code was devised.

Podcasting A podcast is a program made available in digital format for download over the Internet. For example, an episodic series of digital audio or video files that a user can download to a personal device to listen to at a time of their choosing ...

is specifically a pull technology. When a new podcast episode is published to an RSS feed, it sits on the server until it is requested by a feed reader, mobile podcasting app, or directory. Directories such as

Apple Podcasts Apple Podcasts (known as simply Podcasts in Apple operating systems) is an audio streaming service and media player application developed by Apple Inc. for playing podcasts. Apple began supporting podcasts with iTunes 4.9 released in June 200 ...

( iTunes), The Blubrry Directory, and many apps' directories request the RSS feed periodically to update the Podcast's listing on those platforms. Subscribers to those RSS feeds via app or reader will get the episodes when they request the RSS feed next time, independent of when the directory listing updates.

References

Internet terminology Web development {{www-stub

See also

References