cast video, VOD, and interactive broadband services. HFC involves the use of fiber in the backbone and in the access network. The fiber ter- mination point (i.e., the neighborhood node) can support anywhere from 200 to 2,000 homes, with 200 to 500 homes being the norm. From that neighborhood node, coax (normally 750MHz or 1,000MHz) is run to the home, in a two-way subsplit system. (When two cables are not used but there is a need for simulation of a dual-cable system, bandwidth on a single cable can be split up, with one por- tion representing one cable, and the other portion representing the second cable. Splitting the frequencies SO that the lower frequencies are used for one purpose and the higher for another is called a subsplit system.) In countries where there is a history of cable TV, the cable plants have tradi- tionally been one-way analog networks, sending just downstream; after all, what more was required for the conventional broadcast of live television and video pro- gramming? However, to handle Internet access, voice communications, or any other interactive services, a two-way infrastructure is required, SO the operators had to upgrade their networks. Over the past few years, the upgrade to digital two- way systems has been occurring in countries with existing cable infrastructures. other parts of the world, where there had been no MSOs, new systems are being built with digital two-way capabilities, recognizing the need to support today's interactive services environment. A number of elements are involved with a cable TV-based network, including the physical transport infrastructure, generally known as the HFC architecture; cable modems, which are largely standardized under the CableLabs DOCSIS speci- fications; and cable modem controllers, which are known as cable modem termina- tion systems (CMTSs). The following sections discuss these elements. HFC Architecture Cable operators' network infrastructures are based on the HFC architecture, which is in essence a community LAN that uses a bus topology,