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.
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.
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 information is initiated by the receiver or client.
Push services are often based on information preferences expressed in advance. This is called a 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 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 require rejection of incoming HTTP/S requests.