erging operations with these often smaller companies' systems. Comcast Corporation, Cox Cable, and Charter Communication are examples of MSOs in the United States. Using Cable Modems to Access the Internet The basic functions of cable modems are to convert digital signals from computers or data networks to those compatible with coaxial cabling and to convert radio frequency (RF) from cable TV networks to digital signals suitable for Internet access and fiber optical cabling. In cable TV, electromagnetic waves carried on coaxial cabling are referred to as RF signals. The cable TV access network is a hybrid fiber/coax (HFC) network. The Cable Modem "Handshake" Cable modems perform a "handshake," an exchange of signals before data is transmitted to and from the Cable Modem Termination Systems (CMTSs) located at the cable operator site. (See the following section for information regarding CMTS equipment.) Complex signaling, use of frequencies, the speed at which to transmit, and authentication are agreed on between the two devices. At startup, the network checks the user's login before allowing access to the Web or certain web sites. www.TechnicalPDF.com Using Set-Top Boxes to Interface to Cable TV Cable TV set-top boxes are interfaces between televisions, satellite TV, subscription television, and cable TV networks for access to television and other services. At the most basic level, they are tuners that filter out all of the channels except the one selected by the viewer. Because each tuner filters only one channel at a time, set-top boxes used for more than one television simultaneously will require multiple tuners. Personal digital video recorders such as TiVo also have two tuners SO that one tuner filters a channel that is being recorded and the other tuner filters the channel currently being viewed. Other tuners in end users' televisions filter signals for interactive services such as programming guides, VOD, and pay-per-view. Cable operators remotely administer filters and traps in set-top boxes to allow subsc