g the unused spectrum, DSL could use the basic telephone line to carry digital data without interfering with traditional voice services. Initially, the incumbent local exchange carriers (ILECs) were not thrilled with the idea; after all, it would not be as profitable as installing a second Chapter 12 Broadband Access Alternatives telephone line for customers seeking to access the Internet while maintaining their voice connections. In addition, offering a broadband connection stood to cannibal- ize the existing ISDN customers. In the late 1990s, when cable TV companies began to offer broadband Internet access, things changed: ILECs suddenly became very interested in DSL technology, largely due to competitive pressure. Today, DSL is the main competitor to cable modem access when it comes to providing high-speed Internet access to residen- tial users worldwide. As discussed later in this chapter and in Chapter 10, "Next- Generation Networks," service operators are very interested in providing triple-play services (combining the delivery of voice, data, and video) as well as quadruple-play services (which adds wireless services to the mix), and in order to do so, high band- width is mandatory, particularly in the support of HDTV. In general, a DSL implementation includes two main components (see Fig- ure 12.2, on page 505): DSL modem-The DSL modem at the customer premises performs the nec- essary conversion between the digital signals emitted by the computer and the voltage signals required by the network. In the initial deployments of DSL, a technician was required to come to the home and make proper adjustments, including installing a splitter-whose purpose was to separate the voice and data channels-near the demarcation point. However, con- temporary offerings allow subscribers to self-install the equipment. This reduces costs because there is no change required to the cable plant at the customer premises, and no "truck roll" (a physical visit from the techni- cian) is required. Instead, the subscriber simply plug