Flex Session timeout detection on the client?

Question

I am connecting to Java backend(filenet 4.5.1), and I am checking the session in a filter configured to intercept the blazeds calls for MessageBrokerServlet. When the session timesout after 30 mins, the session is invalidated and the blazeds logging shows that the session is invalidated. It disconnects the channel between flex client and blazeds. When I am invoking remote call, since there is no channel, remote call is not going to the server, and the fault handler method is invoked with Client.Error.RequestTimeout after the default timeout for that particular call. How to detect whether channel is there or not? How to detect session timeout and throw message on the client.

Thanks Prashanth