Technologies for chat based on PHP server side [closed]

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I'm searching best technology for web-based chat and PHP server side. I don't know how much visits will have chat. But I think it's 50 users and more in one time开发者_StackOverflow社区.

I have read about long polling, short polling, websockets. But maybe there are more? What advantages have websockets over polling? Are there any libraries for crossbrowser websockets?

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HTML5 WebSockets, Node.js, Comet. All good technologies to use, depends on your specific requirements.