e TV subscribers in the United States are located in areas where they can receive digital cable. Last-Mile Access Networks Lower-Resolution HDTV Digital cable operators implemented digital television in the United States using a different transmission technique than that used for HDTV for over-the-air digital television. (Over-the-air television is delivered by national broadcast- ers such as ABC, NBC, CBS, and Fox from towers to antennas on televisions.) The transmission technique (modulation) refers to how bits are carried over the airwaves. However, standards used by over-the-air broadcasters and specified by the Advanced Television Systems Committee (ATSC) are all based on MPEG-2 compression, a way of encoding and decoding bits before and after they are transmitted. In contrast, the majority of cable operators use the lower-resolution Quadrature Amplitude Modulation (QAM) method. QAM enables providers to pack more digital channels and their associated audio and closed-caption services into the same 6MHz channel than what is specified by ATSC for over- the-air TV in the United States. This frees up capacity for more services and television channels. New HDTV sets are often equipped with ports for QAM as well as ATSC ser- vice. Customers of providers that transmit digital signals using QAM are able to connect their television directly to the cable service without renting a set-top box. However, these customers will only be able to receive over-the-air channels and local access programming, which broadcasts local government and school programming. This is because cable providers scramble premium channels such as HBO and ESPN to prevent piracy. Thus, a customer that wants digital chan- nels, other than those rebroadcast from national broadcasters, must rent a set-top Using Set-Top Boxes to Interface to Cable TV Cable TV set-top boxes are interfaces between televisions, satellite TV, subscrip- tion television, and cable TV networks for access to television and other services. At the most basic level, they are tune