What Is Server Push?
The Server Push mode is a client-server communication in which the dialogue is initiated by the server. This technique is therefore opposed to operating “traditional” web transactions where the customer opens the dialogue, and it pulls the information (pull).
Server Push – Description
To enable its operation, the push technique requires prior authorization from the customer on the subscription model. The customer subscribes to the service whenever new information is available, it is sent by the server.
Applications such as video conferencing or instant messaging are great examples of using this technique: once the central server receives a message (or any other type of data) from one of the participants, the sends to others. The IRC and P2P networks operate on the same principle.
SMTP email works on the principle of server push, although part of the transaction is complete in pull mode (IMAP and POP3). The modern mail clients simulate push by querying the server frequently on the possible arrival of new mail. Note however that the IMAP natively supports push through the IDLE command.
Techniques — HTTP server push
The HTTP server push (sometimes called HTTP streaming) is the name given to the technique applied to push HTTP. Several methods can lead to a push server, the most common being to prevent the server to close the transaction. The client-server connection remains open and, thereby instantly update the data related to customers and avoids creating queues on the server side can be expensive. This feature is available on the Apache server via CGI.
Another possibility is to make the push to use the header Mime multipart / x-mixed-replace, established by the Netscape Navigator browser in 1995. Although most browsers are able to use this header, Microsoft still has no plans to give its browser this technique.
The WHATWG is currently working on the standardization of this technique: the Event Server Sent which, for now, is implemented (in part) as the only browser Opera. Unlike the model developed by Netscape, the event feels server is based on the creation of new Mime type text / event-stream, the data will be used directly through the DOM tree.
The advantage of this method lies in the fact that the customer does not need any applet or plugin to keep its connection open. However, this method suffers from a serious drawback which lies in the timeout allowed in the browser, which involves a manual refresh the page.
Study: From Wikipedia, the free encyclopedia. The text is available under the Creative Commons.
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