reasonable uplink and downlink antennas can accommodate a DS3 (44.736 Mbs) signal in one direction. A full duplex DS3 would require two 36-MHz transponders. Satellite facilities are a better economic approach to point-to-multi- point service, but are only practical where there is a clear, unob- structed line of sight between ground stations and the satellite. As rough rule of thumb, the cross-over point on something like network program distribution is around 15 to 20 multi-points where the requirement is at least 4 hours per day of usage. Once the number of locations goes beyond 20, satellite transmission is far more favor- able and increases in value as the number of locations increase. 4 NETWORK TECHNOLOGY AND METHODOLOGY Optical transmission is somewhat different. Although there are systems that modulate a continuous light wave with a baseband signal, optical transmission techniques in contemporary communi- cations systems and networks use a simple approach-just turn the light wave on and off at the desired repetition rate. For example, a SONET/SDH OC-3/STM4 transmit port operating at 155 Mbs turns the light on and off according to the bit pattern driving it, 155 million times a second, or thereabouts. At the receiving end, the presence or absence of light is detected, converted into a serial bit stream, and subjected to a clock and data recovery process. Fiber Transmission Fiber transmission is several years into its second generation, with unexploited technology in the wings to soak up demand as it grows. Fiber transmission technology and methods began appearing in the 1980s. Fiber transmission bandwidth is many times that of radio spectrum, and its bit-error performance is orders of magnitude better than any known transmission technology. Because fiber is relatively new and likely to be around in an evolving but relatively stable state for the foreseeable future, it seems prudent to explore the subject in more detail. Basically there are two types of fiber conductors: multimode and single mode. Mode refers