Two modem technologies have emerged over the past year for switched data communications services. Cable Modems operate over two-way hybrid fiber/coax and provide user rates as high as 10 Mbps. ADSL Modems (Asymmetric Digital Subscriber Lines) operate over existing copper telephone lines and provide rates as high as 9 Mbps. Both technologies address the large markets for Internet access, remote LAN access for work at home and telecommuting, and network access for the hundreds of millions of personal computers in place today and to be sold over the next ten years. Cable modems may offer more raw speed than ADSL, but that advantage is compromised by inevitable reductions in available cable modem speed. Cable modems share a line with tens of other users; as more users join a line, the capacity available to any one inevitably drops. The top speeds of both technologies will not be usable for years anyway. Internet server speeds, network delays, and personal computer limitations will hold usable rates at or below 2 Mbps for some time. ADSL offers higher security and reliability profiles. Both technologies are at about the same state of maturity and integration. Cable modems may offer a less expensive network solution because of its shared architecture, but that differential is more than offset by infrastructure costs required to upgrade existing networks. The largest advantage of ADSL, and it is a significant one, is the number of telephone lines already installed that can support ADSL, or prospectively available with network upgrades. Today the global ratio is in the order of 400 million to 6 million, or about 60 to 1. Aggressive upgrades will not improve the ratio to better than 10 to 1 in the next five or six years. Even in the United States the ratio today is in the order of 20 to 1, and will not likely get better for CATV suppliers than 3 to 1 over the next five or six years. The end of 1997 will have sold two hundred million personal c...
