sed for modern digital exchanges (we assume such exchanges are SPC based)? 13. Consider one traffic relation that has been designed to meet grade of service objec- tives. We vary one characteristic-the number of traffic channels. Argue the case for efficiency for 10 circuits versus 49 circuits during the BH. Assume grade of service as 0.01 and $1.00 per erlang. 14. Define serving time when dealing with waiting systems (Erlang C). 15. Leaving aside issues of survivability, describe how alternative routing can improve grade of service or allow us to reduce the number of trunks on a traffic relation and still meet grade of service objectives. 16. Why is data traffic SO different from telephone traffic? 17. Distinguish between a tandem/transit switch and a local serving switch. 18. Why use a tandem switch in the first place? 19. What are the three basic requirements of a telephone switch? 20. For a local serving switch with 10,000-line capacity, exemplify concentration ratios (lines/trunks) for a residential area, for an industrial/office area. List six of the eight basic functions of a local switch. 22. Give the three basic functions of a local serving switch. 23. In a very small town, its local serving exchange has only three-digit subscriber numbers. Theoretically, what is the maximum number of subscribers it can serve? 24. How many switch banks will a step-by-step (SXS) switch have if it is to serve up to 10,000 subscribers? 25. What happens to a line that is "busied out?" 26. Give at least three advantages of an SPC exchange when compared with a register- marker crossbar exchange. 27. What are the three basic functional blocks of an SPC exchange (SPC portion only)? Differentiate remote concentrators from remote switches. Give one big advantage each provides. 29. Describe two-wire operation and four-wire operation. 30. What is the function of a hybrid (transformer)? 31. Describe the function of the balancing network as used with a hybrid. REFERENCES 32. There are two new telephone network impairments we usually c