service provides a connection to the Internet through the telephone network. Unlike dial-up, DSL can operate using a single phone line without preventing normal use of the telephone line for voice phone calls. DSL uses the high frequencies, while the low (audible) frequencies of the line are left free for regular telephone communication.[9] These frequency bands are subsequently separated by filters installed at the customer's premises.
DSL originally stood for "digital subscriber loop". In telecommunications marketing, the term digital subscriber line is widely understood to mean Asymmetric Digital Subscriber Line (ADSL), the most commonly installed variety of DSL. The data throughput of consumer DSL services typically ranges from 256 kbit/s to 20 Mbit/s in the direction to the customer (downstream), depending on DSL technology, line conditions, and service-level implementation. In ADSL, the data throughput in the upstream direction, (i.e. in the direction to the service provider) is lower than that in the downstream direction (i.e. to the customer), hence the designation of asymmetric.[36] With a symmetric digital subscriber line (SDSL), the downstream and upstream data rates are equal.[37]
Very-high-bit-rate digital subscriber line (VDSL or VHDSL, ITU G.993.1)[38] is a digital subscriber line (DSL) standard approved in 2001 that provides data rates up to 52 Mbit/s downstream and 16 Mbit/s upstream over copper wires[39] and up to 85 Mbit/s down- and upstream on coaxial cable.[40] VDSL is capable of supporting applications such as high-definition television, as well as telephone services (voice over IP) and general Internet access, over a single physical connection.
VDSL2 (ITU-T G.993.2) is a second-generation version and an enhancement of VDSL.[41] Approved in February 2006, it is able to provide data rates exceeding 100 Mbit/s simultaneously in both the upstream and downstream directions. However, the maximum data rate is achieved at a range of about 300 meters and performance degrades as distance and loop attenuation increases.