COMET - how to know if client disconnected?

Hi,
I implemented a chat using the COMET "way" described in this article:
http://www.codeproject.com/KB/aspnet/CometAsync.aspx
In this example, the client connects for 5 seconds every time.
I wanted to hold the client longer, for about 10 minutes.
My problem is - how to detect if the client disconnected during those 10 minutes?
I tried using Response.IsClientConnected but it returns true even if I close the client.
What else can I check?
There must by some inidicator since the socket gets disconnected if I close the client.

Thanks.

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