How to show message bar on every page

I work with ASP.NET VS2005. In stackoverflow, every now and then, a message bar is displayed at the top of the page. When clicked on the message's hyperlink, it takes me to another page which has all information regarding to the context of the message bar. How do/could I do that?

When bar comes up, it shows on all of the open pages.

I want to show a bar dynamically. In my system, I have 10 users, suppose one user want to save something,开发者_Go百科 I want it to show to all other users after saving. How do/could I do that?

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Here are some asked on SO:
Stackoverflow Style Notifications in asp.net Ajax
Web usability: alert/notification - how to attract attention?

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Sounds like comet or reverse-AJAX. Google will give you more answers now that you know what to look for ;)