How to determine if internet connection is available?

You can use the NetworkInformation class to detect that; this sample code adds an event handler that is called every time connection status changes;

NetworkInformation.NetworkStatusChanged += 
    NetworkInformation_NetworkStatusChanged; // Listen to connectivity changes

static void NetworkInformation_NetworkStatusChanged(object sender)
{
    ConnectionProfile profile = 
        NetworkInformation.GetInternetConnectionProfile();

    if ((profile != null) && profile.GetNetworkConnectivityLevel() >=
                NetworkConnectivityLevel.InternetAccess)
    {
        // We have Internet, all is golden
    }
}

Of course, if you want to just detect it once instead of getting notified when it changes, you can just do the check from above without listening to the change event.

using Windows.Networking.Connectivity;      

public static bool IsInternetConnected()
{
    ConnectionProfile connections = NetworkInformation.GetInternetConnectionProfile();
    bool internet = (connections != null) && 
        (connections.GetNetworkConnectivityLevel() == NetworkConnectivityLevel.InternetAccess);
            return internet;
}