 of less than 3,000 feet. These speeds are only possible on unimpaired cabling. Impairments include bridge taps, where a second cable is spliced (connected) directly to the cable. Impairments are less likely to occur on short cable runs. Worldwide, most carriers offer slower forms of ADSL. Rather than invest in new DSL gear, carriers that own mobile as well as wired facilities invest more heavily in mobile services and fiber-optic cabling to business and commercial buildings. These are more profitable and have a higher potential for revenue than wireline services for individual homes. Certain DSL deployments are considered an intermediate solution until fiber and/or high-speed wireless services gradually replace them. Advances in DSL Technology Advances in DSL technology have made it suitable to use the same copper cabling for last-mile TV and data services as well as for voice. New DSL gear supports high-defini- tion TV, voice, and high-speed Internet access over short lengths of copper cabling. The most advanced DSL service, Very-High-Data-Rate Digital Subscriber Line (VDSL2), supports 200Mbps on cable lengths up to 1,000 feet. The copper cabling transmits Broadband and Wide Area Network Services these signals between a user's premises and a provider's fiber-optic cabling in cabinets or neighborhood nodes. (See Chapter 4, "Carrier Networks," for more information on DSL in conjunction with broadband deployments.) One reason new DSL modems can be used for "triple-play" services (TV, Internet access, and voice calling) is their ability to eliminate noise. On copper cabling, back- ground noise intrudes, or "leaks," from adjacent copper wires (crosstalk) or a nearby electric motor (electromagnetic interference). To prevent transmission degradation and speed loss, advanced DSL services constantly monitor the line for noise. This is com- plex because noise can change over time. Crosstalk is a common impairment on DSL circuits. When crosstalk is detected by specialized equipment, it is eliminated by injecting a matchin