on. HDSL2 provides symmetrical capacities of up to 1.5Mbps or 2Mbps over a single twisted-pair. ADSL ADSL is an asymmetrical service deployed over one twisted-pair. With ADSL, the majority of bandwidth is devoted to the downstream direction, from the network to the user, with a small return path that is generally sufficient to enable telephony or simple commands. ADSL is limited to a distance of about 3.5 miles (5.5 km) from the exchange point. With ADSL, the greater the distance, the lower the data rate; the shorter the distance, the better the throughput. New develop- ments allow the distance to be extended because remote terminals can be placed closer to the customer. There are two main ADSL standards: ADSL and ADSL2. The vast majority of the ADSL that is currently deployed and available is ADSL. ADSL supports up to 7Mbps downstream and up to 800Kbps upstream. This type of bandwidth is suffi- cient to provide good Web surfing, to carry a low grade of entertainment video, and to conduct upstream activities that don't command a great deal of bandwidth. However, ADSL is not sufficient for things such as digital TV or interactive ser- vices. For these activities, ADSL2, which was ratified in 2002, is preferred. ADSL2 Chapter 2 Traditional Transmission Media supports up to 8Mbps downstream and up to 1Mbps upstream. An additional enhancement, known as ADSL2+, can support up to 24Mbps downstream and up to 1Mbps upstream. SDSL SDSL is a symmetrical service that has a maximum loop length of 3.5 miles (5.5 km) and is deployed as a single twisted-pair. It is a good solution in busi- nesses, residences, small offices, and home offices, and for remote access into corpo- rate facilities. You can deploy variable capacities for SDSL, in multiples of 64Kbps, up to a maximum of 2Mbps in each direction. SHDSL SHDSL, the standardized version of SDSL, is a symmetric service that sup- ports up to 5.6Mbps in both the downstream and upstream directions. RADSL RADSL has a maximum loop length of 3.5 miles (5.5 km) and is deployed as a 