ice channel providing voice over DSL (VoDSL) service. 6.4.3.7 Rate-Adaptive DSL (RADSL) An often-used term, RADSL refers to modern DSL technologies, such as ADSL.dmt, SDSL, and VDSL, that can adapt their operation to maximize transmission rates over a cable pair. To achieve this, it adapts loading of each bin to its S/N as explained earlier. However, the DSL access data rate is often set to be fixed and then RADSL technology can ensure that the defined data rate is achieved in various loop conditions. 6.4.3.8 Very-High-Bit-Rate DSL (VDSL) VDSL is an evolving technology that aims to provide access to wider band services via ordinary telephone subscriber pairs. The transmission data rate from the network to the subscriber's premises is up to 52 Mbps and up to 6 Mbps in the opposite direction over a single pair (see Figure 6.21) [5]. Its symmetrical configuration allows an up to 34-Mbps data rate in both direc- tions. The distance over an ordinary cable pair without intermediate repeat- ers is quite short, between 0.1 and 2 km depending on the data rate and loop conditions. Subscriber loops from exchange site are usually longer than VDSL can tolerate and the network-side VDSL equipment has to be installed close to the customer. Then a copper wire DSL part of the circuit might only include the drop line to a residence or business. 6.4.3.9 Summary of the DSL Technologies and Markets As we have seen, many DSL technical alternatives are available and which technology operators choose for their service depends on many things, such Lowpass filter Telephone channel ISDN or telephone exchange Customer Local loop premises Data up to 52 Mbps Internet Data up to 6 Mbps Optical transmission Figure 6.21 VDSL. Data Communications as access network length and quality statistics, competition, and their busi- ness strategies (e.g., residential or business). However, these technologies have important advantages over the competing technologies for high-speed Internet access such as the cable modems of the cable TV networks and ISDN. A