to homes or businesses. When a carrier's account staff determines that there might be a mobile application to increase productivity, it brings in experts to meet with its customer. After learning about the customer's needs, these experts propose a consulting service to develop a software application to address those needs. DIGITAL SUBSCRIBER LINE- DISTANCE LIMITATIONS; OPERATES ON COPPER CABLING Local telephone companies introduced Digital Subscriber Line (DSL) technology in 1989. The telephone companies saw the advantage of using existing copper cabling to combine voice and data on the same copper cabling that was ubiquitous in developed countries. However, DSL has capacity and distance limitations that make it less suitable than transmissions now available over fiber cabling. Higher capacity broadband technologies are replacing DSL in areas with fiber-optic cabling. How DSL Technology Works DSL operates over the same copper cabling used for voice in last-mile networks close to homes and small businesses. Very-High-Data-Rate DSL (VDSL) gear supports high-definition TV, voice, and Internet access over short lengths of copper cabling. The most advanced DSL service, VDSL2, supports 00Mbps on cable lengths up to 1,000 feet. The copper cabling transmits these signals between a user's premises and a provider's fiber- optic cabling in cabinets or neighborhood nodes. (See www.TechnicalPDF.com Table 5-4 in the "Appendix" section at the end of this chapter for information on the types of DSL.) DSL Limitations On copper cabling, background noise intrudes, or "leaks," from adjacent copper wires (crosstalk) or a nearby electric motor (electromagnetic interference). To prevent transmission degradation and speed loss, equipment on advanced DSL services constantly monitor the line for noise. Monitoring is complex because noise can change over time. DSL services over higher frequencies carry more bits in shorter time spans than lower frequencies. Think of it in terms of a commuter subway system: If the trains don't come very oft