(Feed-forward queues). Consider a k station queueing network in which arrivals to server i occur at rate [1]i and service at station i occurs at rate i. We say that the queueing network is feed-forward if the probability of going from i to j < i has p.i; j / D 0. Consider a general three station feed-forward queue. What conditions on the rates must be satisfied for a stationary distribution to exist?