Our first test is to compute the number of seconds since we got some information from our subscription. If it's more than 70 seconds (remember that we configured a maximum interval of 60 seconds), we draw the conclusion that the subscription is no longer active. So we make a new subscription request:

private void SecondTimerCallback(object State) 
{ 
   DateTime Now = DateTime.Now; 
   double SecondsSinceLastEvent = Math.Min( 
         (Now - this.lastEventFields).TotalSeconds, 
         (Now - this.lastEventErrors).TotalSeconds); 
   double SecondsSinceLastOutput =  
         (Now - this.lastOutput).TotalSeconds; 
   RosterItem Item; 
   bool Search = false; 
 
   if (this.subscription != null && SecondsSinceLastEvent > 70) 
         this.SubscribeToSensorData();