Dear NS users, (I'm not sure if I have sent it two times, I'm sorry if I have.) If at time 0, I used the command "$ns at $r proc" to schedule an event that happens at time $r, how can I make the event happen earlier than $r? I mean, after I schedule the event, I want the event to happen at $x (0 < $x < $r), how can I realize this? Your help will be greatly appreciated! S. Wu