To handle chat-related messaging, you could poll the server with Ajax. But to make this application as responsive as possible, you’ll avoid using traditional Ajax as a means to send messages. Ajax uses HTTP as a transport mechanism, and HTTP wasn’t designed for real-time communication. When a message is sent using HTTP, a new TCP/IP connection must be used. Opening and closing connections takes time, and the size of the data transfer is larger because HTTP headers are sent on every request. Instead of employing a solution reliant on HTTP, this application will prefer Web- Socket (http://en.wikipedia.org/wiki/WebSocket), which was designed as a bidirec- tional lightweight communications protocol to support real-time communication. Since only HTML5-compliant browsers, for the most part, support WebSocket, the application will leverage the popular Socket.IO library (http://socket.io/), which provides a number of fallbacks, including the use of Flash, should using WebSocket not be possible. Socket.IO handles fallback functionality transparently, requiring no additional code or configuration. 

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