Server Push vs Server pull in IIS

I was thinking of building a chat application in ASP .NET. I was thinking of eithe开发者_StackOverflowr using push or pull. I have found that pull is more scalable than push. But does any body know if the web chat messenger like gtalk, yahoo etc use pull or push ?.

Thanks.

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Gmail and such are using comet. This is a push architecture.

There is a nice article on ajaxian describing how comet works, this technique is used to push data from the server to the client.

But I am really looking forward the WebSocket, I think it's gonna make a lot of things more easy.