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Server Push

by Anu Rao

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What is it?

Server push is simply when the server (e.g., remote link) sends a series of information blocks to the client (e.g., your browser) in succession. Normally when you click on a link and request a web page, the server sends back the html file and the graphics used in the page. Once the files are sent, the connection between the client and the server is terminated.

A server push sends a chunk of data, whenever it wants, and the browser displays it, leaving the connection open. The connection is not terminated until the server knows it is finished sending data to the client and sends a terminating signal, or the client interrupts the connection.

What is it good/bad for?

The transfer rate is dictated by the load on/speed of the server. Each time a client clicks on a page with a server pushed application, it starts a process on the server. So if 15 people happen to be looking at the page, 15 separate process are started on the server. Perhaps if the server is dedicated to dealing with web-page server push applications (which our server, ame2, is not), this method would be feasible. Many sites have shut down their server push animations due to server disruption/crashes.

The server push method is perhaps most useful when you wish to display rapidly changing information, i.e., things that need to be updated often such as the time, date, etc. For fixed data that is not likely to change from day to day, such as an animation sequence, gifmerge and mpegs make more sense.

Examples

To run the examples multiple times, you need to "Reload" the page each time.

• Animated Clocks
• Simple example from a useful website.

Reference

• Netscape's Exploration of Dynamic Documents (an excellent reference)