Reverse Ajax, Part 2: WebSockets

"WebSockets, which emerged in HTML5, is a much more recent Reverse Ajax technique than Comet. WebSockets enables bi-directional, full-duplex communication channels, and many browsers (Firefox, Google Chrome, and Safari) already support it. The connection is opened through an HTTP request, called a WebSockets handshake, with some special headers. The connection is kept alive, and you can write and receive data in JavaScript as if you were using a raw TCP socket.
A WebSocket URL is started by typing ws:// or wss:// (on SSL).
The timeline in Figure 1 shows communication using WebSockets. An HTTP handshake is sent to the server with specific headers. Then, a type of socket is made available either on the server or on the client side in JavaScript. This socket can be used to asynchronously receive data through an event handler."

for Detaila: see Reverse Ajax, Part 2: WebSockets: