smitting pair. Problem 2.5 Explain the basic principle of telephone call routing through the switching hierarchy to another region of the country. Problem 2.6 A network has N subscribers. Each subscriber is connected directly to all other subscribers. (a) What is the total number of lines L in the network? (b) What is the value of L for N = 2, 10, 100, and 1,000? (c) How many lines must be built to each subscriber? (d) Is this kind of network structure suitable for a public telecommuni- cations network? Explain. Problem 2.7 What are the basic differences between the public and private telecommuni- cations networks? List a few examples of both public and private networks. Problem 2.8 What is ISDN? How does the service and structure of the subscriber inter- face differ from the conventional analog telephone service? Problem 2.9 How does an IN differ from conventional fixed telephone network? List some examples of IN services. Introduction to Telecommunications Network Engineering Problem 2.10 A PBX/PABX has seven telephone channels to a public exchange. During the busy hour, on average, 3.4 lines are occupied. (a) What is the traffic intensity during the busy hour? (b) Estimate, with the help of the Table 2.1, the GoS (blocking probability). Problem 2.11 What is the total offered traffic intensity from a PBX/PABX to PSTN if 10 calls are made, each with a duration of 6 minutes during 1 hour? Problem 2.12 A subscriber makes one 6-minute call in one day between 10:00 and 10:06. What is the average traffic intensity of her subscriber line during (a) 10:00-10:06, (b) 10:00-10:15, (c) 10:00-11:00, and (d) 00:00-24:00 of that day? Problem 2.13 Use the Poisson (or "Molina lost calls held") trunking formula to calculate the blocking probability (GoS) when the total offered traffic is 2 Erl and the number of available transmission channels in the network is 5. Problem 2.14 Draw two curves for GoS levels of 1% and 10%. Use the vertical axis as a ratio Aln from 1% to 100% and the horizontal axis as a number of circuits n from 