if we do assume exponential service-time statistics, with average service time 1/u (or service rate u, in units of call s or setup requests served per unit of time), and Poisson call arrivals at node A (see Fig. 10-2) of average rate r, one get the M/M/N model of Fig. 10-4. This is precisely a birth-death process(see chapter 2 ) with the characterristics