 a single quadra- ture phase shift-keyed bitstream capable of about 30 Mbs payload. Direct satellite service (DSS) facilities occupying a single slot are typically configured with 36-, 54-, or 72-MHz transponders and are typically loaded with subcarriers. Each subcarrier is separated from its neighbors, depending on the amount of bandwidth in the payload it's required to carry. Generally, a 36MHz transponder can accom- modate a DS-3 (44.736 Mbs), depending on uplink antenna size, transmit power and receive antenna size. These variables all accumu- late in a calculation involving reliability, robustness and bit error rate (BER). The lower the error requirement, the more expensive the facility becomes. Terrestrial radio operating in the same band, for example, 4 to 6 GHz or 11 to 12 GHz exhibit similar payload capacity and BER characteristics. Radio channel baseband BER ranges from 10-7 to 10-9. Wireless LANs are proliferating as well, using the 1Ghz spectrum. Bandwidth ranges from 10 to approximately 50 Mbs, depending on equipment and physical free space path distance. Single mode fibers running SONET/SDH optical carrier-based protocol has many times the payload capacity and significantly better BER. An OC-48/STM-16 runs at 2.5Gbs and has a capacity of 48 STS- 1 (51.84 Mbs). Each STS-1 can carry 1 DS-3 and several more T1s. Baseband link performance is in the range of 10-9 to 10 BER. When differentiating between satellite and terrestrial transmission, it's important to consider several factors. These include the nature or topology of the network, reliability, robustness, and error rate per- formance. All things being equal, which of course they aren't in every detail, but at a high level, satellite networks tend to be more cost- effective and reliable in point-to-multiple-point topology than terres- 5 NETWORK ARCHITECTURE, FACILITIES, AND SERVICES trial networks. This is not a fiber VS. radio technology consideration; it's a physical consideration. Fundamentally, the satellite transponder is the common source for 