Very high-speed Digital Subscriber Line (V. D. S. L.) and Very high-speed Digital Subscriber Line 2 (V. D. S. L. 2) are digital subscriber line (D. S. L.) technologies providing data transmission faster than Asymmetric Digital Subscriber Line (A. D. S. L.).
V. D. S. L. offers speeds of up to 52 Mbit/s downstream and 16 Mbit/s upstream, over a single flat untwisted or twisted pair of copper wires using the frequency band from 25 kHz to 12 MHz. These rates mean that V. D. S. L. 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 connection. V. D. S. L. is deployed over existing wiring used for analog telephone service and lower-speed DSL connections. This standard was approved by the International Telecommunication Union (ITU) in November 2001.
Second-generation systems (V. D. S. L. 2; ITU-T G.993.2 approved in February 2006) use frequencies of up to 30 MHz to provide data rates exceeding 100 Mbit/s simultaneously in both the upstream and downstream directions. The maximum available bit rate is achieved at a range of about 300 metres (980 ft); performance degrades as the local loop attenuation increases.
The concept of V. D. S. L. was first published in 1991. through a joint Bellcore-Stanford research study. The study searched for potential successors to the then-prevalent H. D. S. L. and relatively new A. D. S. L., which were both 1.5 Mbit/s. Specifically, it explored the feasibility of symmetric and asymmetric data rates exceeding 10 Mbit/s on short phone lines.
V. D. S. L. 2 standard is an enhancement to ITU T G.993.1 that supports asymmetric and symmetric transmission at a bidirectional net data rate up to 400 Mbit/s on twisted pairs using a bandwidth up to 35 MHz.
V. D. S. L. standards
A V. D. S. L. connection uses up to seven frequency bands, so one can allocate the data rate between upstream and downstream differently depending on the service offering and spectrum regulations. The first-generation V. D. S. L. standard specified both quadrature amplitude modulation (QAM) and discrete multi-tone modulation (D. M. T.). In 2006., ITU-T standardized V. D. S. L. in recommendation G.993.2 which specified only DMT modulation for V. D. S. L. 2.
|Version||Standard name||Common name||Downstream rate||Upstream rate||Approved on|
|V. D. S. L.||ITU G.993.1||V. D. S. L.||55 Mbit/s||3 Mbit/s||2001-11-29|
|V. D. S. L. 2||ITU G.993.2||V. D. S. L. 2||200 Mbit/s||100 Mbit/s||2006-02-17|
|V. D. S. L. 2-Vplus||ITU G.993.2
Amendment 1 (11/15)
|V. D. S. L. 2 Annex Q
|300 Mbit/s||100 Mbit/s||2015-11-06|
V. D. S. L. 2
V. D. S. L. is an enhancement to V. D. S. L. Designed to support the wide deployment of triple play services such as voice, video, data and high-definition television (H. D. T. V.) V. D. S. L. 2 is intended to enable operators and carriers to gradually, flexibly, and cost-efficiently upgrade existing x. D. S. L. infrastructure.
The protocol is standardized in the International Telecommunication Union telecommunications sector (ITU-T) as Recommendation G.993.2. It was announced as finalized on 27 May 2005, and first published on 17 February 2006. Several corrections and amendments were published from 2007 to 2011.
V. D. S. L. 2 permits the transmission of asymmetric and symmetric aggregate data rates up to 300+ Mbit/s downstream and upstream on twisted pairs using a bandwidth up to 35 MHz. It deteriorates quickly from a theoretical maximum of 350 Mbit/s at source to 100 Mbit/s at 500m (1640.42ft) and 50 Mbit/s at 1000m (3280.84ft), but degrades at a much slower rate from there, and outperforms V. D. S. L. Starting from 1,600 m (1 mi) its performance is equal to A. D. S. L. 2+.
A. D. S. L.-like long-reach performance is one of the key advantages of V. D. S. L. 2. L. R.-V. D. S. L. 2 enabled systems are capable of supporting speeds of around 1–4 Mbit/s (downstream) over distances of 4–5 km (2.5–3 miles), gradually increasing the bit rate up to symmetric 100 Mbit/s as loop-length shortens. This means that V. D. S. L. 2-based systems, unlike V. D. S. L. systems, are not limited to short local loops or M. T. U./M. D. U.s only,[clarification needed] but can also be used for medium range applications.
Bonding (ITU-T G.998.x) may be used to combine multiple wire pairs to increase available capacity, or extend the copper network's reach. Hybrid Access Networks  can be used to combine X. D. S. L. with wireless networks. This enables network operators to provide faster Internet access services over long lines.
Vplus is a technology to achieve higher speeds over existing VDSL2 networks. It was developed by Alcatel-Lucent and standardised in November 2015 in ITU G.993.2 Amendment 1 as V. D. S. L. 2 profile 35b. It promises to deliver speeds of up to 300 Mbit/s downstream and 100 Mbit/s upstream on loops shorter than 250 m. On longer loops, Vplus falls back to V. D. S. L. 2 17a vectoring performance. Vplus uses the same tone spacing as V. D. S. L. 2 17a to allow vectoring across Vplus (35b) and 17a lines, and thus mixed deployments and a smooth introduction of Vplus.
The V. D. S. L. 1 standard has three bandplans: Annex A (Asymmetric BandPlan), Annex B (Symmetric BandPlan) and Annex C (Fx BandPlan). Annex A and Annex B were formerly called Plan 998 and Plan 997 respectively. V. D. S. L. 1 Annex C is intended for use in Sweden only and it uses a variable separating frequency between the second downstream band, and the second upstream band. All VDSL1 bandplans have spectrum up to 12 MHz, so the length of the copper loops must be shorter than A. D. S. L.
The V. D. S. L. 2 standard defines a wide range of profiles that can be used in different V. D. S. L. deployment architectures; in the central office, in the cabinet or in the building for example.
V. D. S. L. 2 vectoring
Vectoring is a transmission method that employs the coordination of line signals for reduction of crosstalk levels and improvement of performance. It is based on the concept of noise cancellation, much like noise-cancelling headphones. The ITU-T G.993.5 standard, "Self-FEXT cancellation (vectoring) for use with V. D. S. L. 2 transceivers" (2010), also known as G.vector, describes vectoring for V. D. S. L. 2. The scope of Recommendation ITU-T G.993.5 is specifically limited to the self-FEXT (far-end crosstalk) cancellation in the downstream and upstream directions. The far end crosstalk (F. E. X. T.) generated by a group of near-end transceivers and interfering with the far-end transceivers of that same group is cancelled. This cancellation takes place between V. D. S. L. 2 transceivers, not necessarily of the same profile. The technology is analogous to G.IMP and Seamless Rate Adaptation (S. R. A.).
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- "VDSL Speed". HowStuffWorks.
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- Broadband Forum (2016-07-01). "TR-348 Hybrid Access Broadband Network Architecture" (PDF). Retrieved 2018-07-01.
- Keith Russell; Paul Spruyt; Stefaan Vanhastel (16 October 2014). "Vplus gets more out of VDSL2 vectoring". Alcatel-Lucent. Archived from the original on 25 July 2015.
- tsbmail (2013-06-14). "G.993.5 : Self-F. E. X. T. cancellation (vectoring) for use with V. D. S. L. 2 transceivers". Itu.int. Retrieved 2013-07-04.