ERENCES 9. What is the switch design limit of RD, of RRD? 10. Where will we apply long route design (LRD)? 11. Define a range extender. 12. With RRD, on loops greater than 1500 S2, what expedients do we have using stan- dardized design rules? 13. What kind of inductive loading is used with RRD? 14. Beyond what limit on a subscriber loop is it advisable to employ DLC? 15. For VF trunks, if D is the distance between load coils, why is the first load coil placed at D/2 from the exchange? 16. Define a main frame. 17. What does line build-out do? 18. What are the two types of VF repeaters that may be used on VF trunks or subscriber loops? What are practical gain values used on these amplifiers? REFERENCES 1. The IEEE Standard Dictionary of Electrical and Electronics Terms, 6th ed., IEEE Std-100-1996, IEEE, New York, 1996. 2. Transmission Systems for Communications, 5th ed., Bell Telephone Laboratories, Holmdel, NJ, 1982. 3. W. F. Tuffnell, 500-Type Telephone Sets, Bell Labs Record, Bell Telephone Laboratories, Holmdel, NJ, September 1951. 4. Outside Plant, Telecommunication Planning Documents, ITT Laboratories Spain, Madrid, 1973. 5. BOC Notes on the LEC Networks-1994. Bellcore, Livingston, NJ, 1994. 6. Telecommunication Transmission Engineering, 2nd ed., Vols. 1-3, American Telephone and Telegraph Co., New York, 1977. 7. R. L. Freeman, Telecommunication Transmission Handbook, 4th ed., Wiley, New York, 1998. DIGITAL NETWORKS 6.1 INTRODUCTION TO DIGITAL TRANSMISSION The concept of digital transmission is entirely different than its analog counterpart. With an analog signal there is continuity-as contrasted with a digital signal, which is concerned with discrete states. The information content of an analog signal is conveyed by the value or magnitude of some characteristic(s) of the signal such as amplitude, frequency, or phase of a voltage, the amplitude or duration of a pulse, the angular position of a shaft, or the pressure of a fluid. To extract the information, it is necessary to compare the value or magnitude of t