1 to 20. Use traffic engineering Table 2.1. What can you say about net- work utilization when the number of circuits n is small? How does the utili- zation of the circuits depend on the allowed probability of blocking? Problem 2.15 What will the approximate capacity of a network be (i.e., how many channels should be available) if there are 100 subscribers and each of them generates offered traffic of 40 mErl? The probability of blocking is (a) 20% and (b) 1%. Use traffic engineering Table 2.1. Problem 2.16 There are 20 users of a keyphone system that has two lines to a public net- work. What is the blocking probability when each user generates a 100-mErl offered traffic? The Telecommunications Network: An Overview Problem 2.17 A keyphone system with three lines to the local exchange is used in an office of 10 persons. Each of them uses the phone for an external call of 15 minutes in a busy hour. How many lines are reserved on average during an hour? What is the blocking probability? What do you think about the capacity of this system? Problem 2.18 Subscribers of a local exchange generate 100 mErl of traffic through the exchange to the network. What should the number of trunk channels be if the number of subscribers in the area is (a) 10, (b) 100, (c) 1,000, and (d) 4,000? The allowed blocking level is 1%. Use Table 2.1 to estimate the required number of circuits. References [1] Telecommunications Transmission Engineering, Bellcore Technical Publications, 1990. [2] Freeman, R. L., Telecommunication System Engineering, 3rd ed., New York: John Wiley & Sons, 1996. Freeman, R. L., Fundamentals of Telecommunications, New York: John Wiley & Sons, 1999. Signals Carried over the Network Services that the telecommunications networks provide have different char- acteristics. Required characteristics depend on the applications we use. To meet these different requirements, many different network technologies that are optimized for each type of service are in use. To understand the present structure of the telecommunications n