System A consists of a single ring with 100 stations, one per repeater. System B consists of four 25 stations rings linked by a bridge. If the probability of a link failureis Pl, a repeater failure is Pr , and a bridge failure is Pb , derive an expression for parts (a) to (e).

a) Probability of failure of system A.
b) Probability of complete failure of system B.
c) Probability that a particular station will find the network unavailable, for
systems A and B.
d) Probability that any two stations selected at random will be unable to
communicate for systems A and B.
e) Compare values of parts (a) and (b) for Pl = Pb = Pr = 10^-2 .