Cable Modems, For and Against

Cable modems send and receive data from a TV coaxial cable, typically connecting to a PC via 10Base-T Ethernet. Download speeds on the coaxial cable are typically 10 Mbps, although some vendors tout speeds as fast as 40 Mbps. Uploads are usually in the 0.5- to 2-Mbps range, but 10 Mbps is possible.

Cable-modem detractors point out that since this cable bandwidth is shared (as on a LAN), if 100 subscribers are active on a 10-Mbps wire, the bandwidth available to each is only 0.1 Mbps. They assert the superi ority of a switched Ethernet environment, a model similar to that of the familiar voice-telephone system.

The same architecture is the basis of the Digital Subscriber Line (DSL) services now being pushed by the phone companies. With a switched architecture, you're temporarily connected to the destination endpoint, and the bandwidth is all yours. But DSL services are not yet commercially available, and since the Internet portion of the link puts users back onto a shared resource, we wonder if switched networks might provide only a small, temporary advantage.

Still, our tests indicate that cable modems offer by far the fastest Internet access of any technology currently available. And we believe that cable operators can easily segment their systems to accommodate a growing number of users, much as LAN managers do today. Nobody puts 100 users on an Ethernet; rather, they put 10 users on each of 10 segments. In fact, we were unable to find out from MediaOne exactly how many subscribers were on our cable system.