Server-based Chat

Described on this scheme "Server Clients Scheme" I try to create a Silverlight / Server Application which has EventHandler/Triggers, which can do the following:

• Notice whether a message was sent to "it" (the server)
• Notice that the sent message is new "to all" "except" "the sender"
• Send开发者_StackOverflow社区 "to all" ("except...") "new message can be downloaded" / or even the new messages

How could this be done by using: ASP.NET and Silverlight?

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Here is a starting point: http://www.codeproject.com/KB/silverlight/BuildASilverlight2WebChat.aspx