A group of n processors is arranged in an ordered list. When a job arrives, the ?rst processor in line attempts it; if it is unsuccessful, then the next in line tries it; if it too is unsuccessful, then the next in line tries it, and so on. When the job is successfully processed or after all processors have been unsuccessful, the job leaves the system. At this point we are allowed to reorder the processors, and a new job appears. Suppose that we use the one-closer reordering rule, which moves the processor that was successful one closer to the front of the line by interchanging its position with the one in front of it. If all processors were unsuccessful (or if the processor in the ?rst position was successful), then the ordering remains the same. Suppose that each time processor i attempts a job then, independently of anything else, it is successful with probability pi.

(a) De?ne an appropriate Markov chain to analyze this model.

(b) Show that this Markov chain is time reversible.

(c) Find the long-run probabilities.