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, or get, where the request for the transmission of information is initiated by the receiver or client.[1]

Push services are often based on information and data preferences expressed in advance, called the publish-subscribe model. A client "subscribes" to various information channels provided by a server; whenever new content is available on one of those channels, the server "pushes" or "publishes" that information out to the client.

Push is sometimes emulated with a polling technique, particularly under circumstances where a real push is not possible, such as sites with security policies that reject incoming HTTP requests.