This operator has 4 powerful EWSD switches for its fixed network, has 6 Mobile Switching Centres. As the operator claims “all switches are interconnected to compensate for any failure that might occur”. Has an optical DWDM transmission network (not just WDM!), whose city-rings only carry a capacity of 200 Gbps.
What is the probability that this operator may have congestions only because of extra 120 calls from its telephone network to its mobile network, assuming that its network experienced no congestion problem and was very reliable before that 120 calls?