Push technology or server push is used to send information to the client by itself without requiring a request from the client. It goes under the publish/subscribe paradigm. The other frequently used method is pull method where the client sends a request to initiate the transmission.
Applications include most of the emailing systems like gmail etc.... And the famous smtp protocol uses push technology. This technology removes the requirement of polling which has high overhead.
This can be done in several ways.
- Http server push : Here the server does not terminate the connection with the client after serving it's request. There fore it can send information to one or more clients easily. This is implemented using CGI in many systems.
- pushlets : This is a java technology. It never terminates the response. That is even if the response is sent to the browser, the response is not terminated. Therefore the browser does not know that the content is fully sent. Whenever the server wants to send information, it sends via javascript and eliminates the requirement of java applet. One draw back is it cannot handle the browser timeout. Therefore need to refresh the page periodically overcome the drawback.
- long polling : This is like normal polling in a way. client ask for data and the request is sent to server. How ever the server does not send the response until it has some new data. When ever it has new data, it sends a full response to the client. Then again after that the client needs to poll.
Apart from the above there are some other methods as well like flas xml socket relays, xmpp etc...
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