Whether Silverlight 3 application is running online or not

Just check the below mentioned property to know the network status of Silverlight application.We can do operations according to that.
Application.Current.ExecutionState

There are 5 possible states which are defined in System.Windows.ExecutionStates

// Summary:
//     Defines constants that indicate the state of an application that can run
//     offline.
public enum ExecutionStates
{
    // Summary:
    //     The application is running within its host Web page.
    RunningOnline = 0,
    //
    // Summary:
    //     The application is in the process of detaching from its host Web page.
    Detaching = 1,
    //
    // Summary:
    //     The application is running in offline mode, detached from its host Web page.
    Detached = 2,
    //
    // Summary:
    //     The application is running in offline mode, but a newer version of the application
    //     has been downloaded and will be used the next time the application is launched.
    DetachedUpdatesAvailable = 3,
    //
    // Summary:
    //     The application could not be detached from its host Web page.
    DetachFailed = 4,
}