ess noise and availability of the reverse channel (upstream) bandwidth. If the design can be deployed in this configuration, the infra- structure upgrade cost for cable systems will be minimal. In the future, the availability of midsplit or highsplit cable plants will enable a physical (PHY) layer with enhanced performance. 17.9 OTHER GENERAL INFORMATION 17.9.1 Frequency Reuse The assumption is made that the coaxial cable traffic for each service area will be able to use the entire 5-30/5-42-MHz reverse bandwidth. This could be done either by use of a separate return fiber for each service area or by use of a single fiber for several service areas, whose return traffic streams would be combined using block frequency translation at the fiber node. 17.9.2 Cable Distance Limitations The distance coverage of the system can be influenced by several factors such as the fiber-optic technology employed and the coaxial cable distribution topology. The limiting factor could be the number of active amplifiers and the resulting noise parameters that must be bounded for an optimal physical design. To budget delay use 5 usec/km for optical fiber and 4 usec/km for coaxial cable. REVIEW EXERCISES 1. Define a CATV headend. What are its functions? 2. List at least three impairments we can expect from a broadband CATV amplifier (downstream). A signal splitter divides a signal in half, splitting into two equal power levels. If the input to a 3-dB splitter were -7 dBm (in the power domain), then the output on each leg would be -10 dBm. Is this a true statement? What is missing here? Subsplit is a frequency division scheme that allows bidirectional traffic on a single cable. Reverse path signals come to the headend from 5 to 30 MHz, and up to 42 MHz on newer systems. Forward path (downstream) signals go from the headend to end-users from 54 MHz to the upper frequency limit of the system in question. REFERENCES 4. What was/is the purpose of LOS microwave at a CATV headend? 5. What is the purpose of a set-top converter? 6. What does the