Unable to catch CommunicationException in Async Service Call

Question

I have a WCF service and my client is a Silverlight application. When the service goes down (network error etc.) then I get this exception on the client proxy:

CommunicationException: The communication object, System.ServiceModel.Channels.ClientFramingDuplexSessionChannel, cannot be used for communication because it is in the Faulted state.

to be precise, on the 5th line of the code below:

public System.IAsyncResult BeginPublishVideo(byte[] data, System.AsyncCallback callback, object asyncState) {
                object[] _args = new object[1];
                _args[0] = data;
                //Below is when the exception is received
                System.IAsyncResult _result = base.BeginInvoke("PublishVideo", _args, callback, asyncState);
                return _result;
            }

So I've tried wrapping up the service call (from the stack trace) in a try/catch but to no avail, the try/catch doesn't ever get executed. Basically this:

        try
        {
            _videoClient.PublishVideoAsync(codedVideoBuffer);
        }
        catch (Exception) { }

But the try catch never gets hit. How can I catch this exception and deal with it gracefully?

TIA.