retransmitter = new AckSenderWindow(new Command(), AVG_RETRANSMIT_INTERVAL);
	public void start() throws Exception {            TimeScheduler timer;                        timer = stack != null ? stack.timer : null;	    if(timer == null)                throw new Exception("TOTAL.start(): timer is null");                        reqTbl       = new TreeMap();            upTbl        = new TreeMap();            retransmitter = new AckSenderWindow(new Command(), AVG_RETRANSMIT_INTERVAL);	}