s DSL filters into each telephone outlet. This approach, while easier and less costly, can cause deg- radation in performance, particularly if there are many devices connected to the one DSL line, because the DSL signal will be present on all the tele- phone wiring throughout the home or building. Nonetheless, this is the most common approach today. DSL access multiplexer (DSLAM)-A DSLAM terminates and aggregates a large number of DSL subscriber lines, separating the voice and data traffic before handing it off to the proper network, either the PSTN for traditional circuit-switched voice calls or a packet network (ATM, IP, or MPLS) for the data and multimedia traffic. Characteristics and Properties of DSL A number of factors determine whether you get the kind of service that DSL prom- ises and that you expect. The performance of any of the DSL alternatives is highly DSL Technology dependent on the loop length as well as the loop condition because a host of impairments can affect the performance of a given pair of copper wires. DSL modems generally range up to a maximum of about 3.5 miles (5.5 km), although new specifications are constantly being created to increase the permitted distances. The general rule of thumb with DSL is that the greater the distance, the lower the performance, and the shorter the distance, the greater the data rate possible. The original ADSL standards, using twisted-pair copper, can deliver up to 7Mbps downstream over a distance of about 1.25 miles (2 km). The latest ADSL stan- dards, such as ADSL2+, can deliver up to 24Mbps downstream, but this rate depends on the distance between the customer and the DSLAM, the point at which numerous subscriber lines are first terminated and aggregated before connecting to the PSTN (for traditional circuit-switched voice) or packet-based backbone (for data and multimedia) local exchange and then onward to the PSTN or packet back- bone; in order to deliver 24Mbps downstream, the maximum distance allowed is roughly 1 mile (1.5 km). With one version of VD