Pull technology

Not to be confused with Push–pull technology.

Pull coding or client pull is a style of network communication where the initial request for data originates from the client, and then is responded to by the server. The reverse is known as push technology, where the server pushes data to clients. Usually, customers will look for a site and visit only if it provides helpful and attractive content to display. The pull code is effective and economical when advertising to open, unidentified potential customers world wide. It is more effective for the customer when he searches for a specific item.

Pull requests form the foundation of network computing, where many clients request data from centralised servers. Pull is used extensively on the Internet for HTTP page requests from websites.

A push can also be simulated using multiple pulls within a short amount of time. For example, when pulling POP3 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 in order to function correctly.

Most web feeds, such as RSS are technically pulled by the client. With RSS, the user's RSS reader 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. For solving this problem, the PubSubHubbub protocol as another example of a push code was devised.

See also

• Push technology
• Client–server model