VDSL

Last updated
VDSL
Very high speed digital subscriber line transceivers
StatusIn force
Year started2001
Latest version(11/15)
November 2015
Organization ITU-T
Committee ITU-T Study Group 15
Related standards G.993.1, G.993.2
Domain telecommunications
LicenseFreely available
Website www.itu.int/rec/T-REC-G.993.2

Very high-speed digital subscriber line (VDSL) [1] and very high-speed digital subscriber line 2 (VDSL2) [2] are digital subscriber line (DSL) technologies providing data transmission faster than the earlier standards of asymmetric digital subscriber line (ADSL) G.992.1, G.992.3 (ADSL2) and G.992.5 (ADSL2+).

Contents

VDSL offers speeds of up to 52  Mbit/s downstream and 16 Mbit/s upstream, [3] over a single twisted pair of copper wires using the frequency band from 25  kHz to 12 MHz. [4] These rates mean that 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 connection. VDSL 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 (VDSL2; ITU-T G.993.2 approved in February 2006) [5] 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.

Conceptual development

The concept of VDSL was first published in 1991 through a joint Bellcore-Stanford research study. The study searched for potential successors to the then-prevalent HDSL and relatively new ADSL, 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.

VDSL2 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.

VDSL standards

DSL SoC Lantiq XWAY VRX288 V1.1.png
DSL SoC

A VDSL 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 VDSL standard specified both quadrature amplitude modulation (QAM) and discrete multi-tone modulation (DMT). In 2006, ITU-T standardized VDSL in recommendation G.993.2 which specified only DMT modulation for VDSL2.

VersionStandard nameCommon nameDownstream rateUpstream rateApproved on
VDSLITU G.993.1VDSL55 Mbit/s3 Mbit/s2001-11-29
VDSL2ITU G.993.2VDSL2200 Mbit/s100 Mbit/s2006-02-17
VDSL2-VplusITU G.993.2
Amendment 1 (11/15)		VDSL2 Annex Q
VPlus/35b		300 Mbit/s100 Mbit/s2015-11-06

VDSL2 frequencies.png

VDSL2

A VDSL2 cabinet on top of a copper cabling cabinet in Italy. Armadio PSTN con zainetto G.fast.jpg
A VDSL2 cabinet on top of a copper cabling cabinet in Italy.

VDSL2 is an enhancement to VDSL designed to support the wide deployment of triple play services such as voice, video, data and high-definition television (HDTV) VDSL2 is intended to enable operators and carriers to gradually, flexibly, and cost-efficiently upgrade existing xDSL 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, [5] and first published on 17 February 2006. Several corrections and amendments were published from 2007 to 2011. [2]

VDSL2 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 on its latest version. [6] It deteriorates quickly from a theoretical maximum of 350 Mbit/s at source to 100 Mbit/s at 500 m (1640.42 ft) and 50 Mbit/s at 1000 m (3280.84 ft), but degrades at a much slower rate from there, and outperforms VDSL. Starting from 1,600 m (1 mi) its performance is equal to ADSL2+. [7]

A VDSL2 DSLAM Cabinet installed by PCCW in Pat Heung, Hong Kong. PCCW DSLAM Cabinet.jpg
A VDSL2 DSLAM Cabinet installed by PCCW in Pat Heung, Hong Kong.
An Openreach engineer works at a UK VDSL cabinet Openreach Man at cabinet.jpg
An Openreach engineer works at a UK VDSL cabinet

ADSL-like long-reach performance is one of the key advantages of VDSL2. LR-VDSL2 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 VDSL2-based systems, unlike VDSL systems, are not limited to short local loops or MTU/MDUs 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 [8] can be used to combine xDSL with wireless networks. This enables network operators to provide faster Internet access services over long lines.

Vplus/35b

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 VDSL2 profile 35b. [2] 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 VDSL2 17a vectoring performance. [9] Vplus uses the same tone spacing as VDSL2 17a to allow vectoring across Vplus (35b) and 17a lines, and thus mixed deployments and a smooth introduction of Vplus. [9]

Profiles

The VDSL1 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. VDSL1 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 ADSL. [10] [11]

The VDSL2 standard defines a wide range of profiles that can be used in different VDSL deployment architectures; in the central office, in the cabinet or in the building for example. [12]

Profile Bandwidth
(MHz)		Number of
total
carriers 		Carrier
bandwidth
(kHz)		Maximum aggregate
downstream transmit
power (dBm)		Max. downstream
throughput
(Mbit/s)		Max. upstream
throughput
(Mbit/s)
8a8.83220484.3125+17.55016
8b8.83220484.3125+20.55016
8c8.50019724.3125+11.55016
8d8.83220484.3125+14.55016
12a1227834.3125+14.56822
12b1227834.3125+14.56822
17a17.66440964.3125+14.515050
30a30.00034798.625+14.5230100
35b35.32881924.3125+17.0300100

VDSL2 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 VDSL2 transceivers" (2010), also known as G.vector, describes vectoring for VDSL2. 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 (FEXT) 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 VDSL2 transceivers, not necessarily of the same profile. [13] [14] The technology is analogous to G.INP and Seamless Rate Adaptation (SRA). [15]

Although technically feasible, as of 2022, vectoring is incompatible with local-loop unbundling, but future standard amendments could bring a solution.[ citation needed ]

VDSL2+ Supervectoring

Supervectoring  [ de ] is an evolution of the vectoring technology invented and widely implemented by Deutsche Telekom, [16] [17] which further increases crosstalk and interference resistance and allows for stable internet at home connections at 250  Mbit/s downstream and 100 Mbit/s upstream.

See also

Related Research Articles

Digital subscriber line is a family of technologies that are used to transmit digital data over telephone lines. In telecommunications marketing, the term DSL is widely understood to mean asymmetric digital subscriber line (ADSL), the most commonly installed DSL technology, for Internet access.

A symmetric digital subscriber line (SDSL) is a digital subscriber line (DSL) that transmits digital data over the copper wires of the telephone network, where the bandwidth in the downstream direction, from the network to the subscriber, is identical to the bandwidth in the upstream direction, from the subscriber to the network. This symmetric bandwidth can be considered to be the opposite of the asymmetric bandwidth offered by asymmetric digital subscriber line (ADSL) technologies, where the upstream bandwidth is lower than the downstream bandwidth. SDSL is generally marketed at business customers, while ADSL is marketed at private as well as business customers.

<span class="mw-page-title-main">DSLAM</span> Network device that connects DSL interfaces to a digital communications channel

A digital subscriber line access multiplexer is a network device, often located in telephone exchanges, that connects multiple customer digital subscriber line (DSL) interfaces to a high-speed digital communications channel using multiplexing techniques. Its cable internet (DOCSIS) counterpart is the cable modem termination system.

Single-pair high-speed digital subscriber line (SHDSL) is a form of symmetric digital subscriber line (SDSL), a data communications technology for equal transmit and receive data rate over copper telephone lines, faster than a conventional voiceband modem can provide. As opposed to other DSL technologies, SHDSL employs trellis-coded pulse-amplitude modulation (TC-PAM). As a baseband transmission scheme, TC-PAM operates at frequencies that include those used by the analog voice plain old telephone service (POTS). As such, a frequency splitter, or DSL filter, cannot be used to allow a telephone line to be shared by both an SHDSL service and a POTS service at the same time. Support of symmetric data rates made SHDSL a popular choice by businesses for private branch exchange (PBX), virtual private network (VPN), web hosting and other data services.

Rate-adaptive digital subscriber line (RADSL) is a pre-standard asymmetric digital subscriber line (ADSL) solution. RADSL was introduced as proprietary technology by AT&T Paradyne, later GlobeSpan Technologies Inc., in June 1996. In September 1999, RADSL technology was formally described by ANSI in T1.TR.59-1999. RADSL supports downstream data rates of up to approximately 8 Mbit/s, upstream data rates up to approximately 1 Mbit/s, and can coexist with POTS voice on the same line.

<span class="mw-page-title-main">G.992.5</span> Technology for broadband Internet access

G.992.5 is an ITU-T standard for asymmetric digital subscriber line (ADSL) broadband Internet access. The standard has a maximum theoretical downstream sync speed of 24 megabits per second (Mbit/s). Utilizing G.992.5 Annex M upstream sync speeds of 3.3 Mbit/s can be achieved.

Carrierless amplitude phase modulation (CAP) is a variant of quadrature amplitude modulation (QAM). Instead of modulating the amplitude of two carrier waves, CAP generates a QAM signal by combining two PAM signals filtered through two filters designed so that their impulse responses form a Hilbert pair. If the impulse responses of the two filters are chosen as sine and a cosine, the only mathematical difference between QAM and CAP waveforms is that the phase of the carrier is reset at the beginning of each symbol. If the carrier frequency and symbol rates are similar, the main advantage of CAP over QAM is simpler implementation. The modulation of the baseband signal with the quadrature carriers is not necessary with CAP, because it is part of the transmit pulse.

In telecommunications, ITU G.992.2 is an ITU standard for ADSL using discrete multitone modulation. G.lite is designed to not require the use of a DSL filter.

<span class="mw-page-title-main">G.992.3</span> ITU-T Recommendation

ITU G.992.3 is an ITU standard, also referred to as ADSL2 or G.dmt.bis. It optionally extends the capability of basic ADSL in data rates to 12 Mbit/s downstream and, depending on Annex version, up to 3.5 Mbit/s upstream. ADSL2 uses the same bandwidth as ADSL but achieves higher throughput via improved modulation techniques. Actual speeds may decrease depending on line quality; usually the most significant factor in line quality is the distance from the DSLAM to the customer's equipment.

Uni-DSL (UDSL) in telecommunications is a digital subscriber line (DSL) marketing buzzword developed by Texas Instruments which would provide bit rates of at least 200 Mbit/s in aggregate on the downstream and upstream paths. UDSL is backwards compatible with all discrete multitone modulation (DMT) standards.

Ethernet in the first mile (EFM) refers to using one of the Ethernet family of computer network technologies between a telecommunications company and a customer's premises. From the customer's point of view, it is their first mile, although from the access network's point of view it is known as the last mile.

<span class="mw-page-title-main">G.992.5 Annex M</span> ITU-T Recommendation

Annex M is an optional specification in ITU-T recommendations G.992.3 (ADSL2) and G.992.5 (ADSL2+), also referred to as ADSL2 M and ADSL2+ M. This specification extends the capability of commonly deployed Annex A by more than doubling the number of upstream bits. The data rates can be as high as 12 or 24 Mbit/s downstream and 3 Mbit/s upstream depending on the distance from the DSLAM to the customer's premises.

High-bit-rate digital subscriber line (HDSL) is a telecommunications protocol standardized in 1994. It was the first digital subscriber line (DSL) technology to use a higher frequency spectrum over copper, twisted pair cables. HDSL was developed to transport DS1 services at 1.544 Mbit/s and 2.048 Mbit/s over telephone local loops without a need for repeaters. Successor technology to HDSL includes HDSL2 and HDSL4, proprietary SDSL, and G.SHDSL.

The prevalent means of connecting to the Internet in Germany is DSL, introduced by Deutsche Telekom in 1999. Other technologies such as Cable, FTTH and FTTB (fiber), Satellite, UMTS/HSDPA (mobile) and LTE are available as alternatives.

<span class="mw-page-title-main">G.992.3 Annex J</span> ITU-T Recommendation

Annex J is a specification in ITU-T Recommendations G.992.3 and G.992.5 for all digital mode ADSL with improved spectral compatibility with ADSL over ISDN, which means that it is a type of naked DSL which will not disturb existing Annex B ADSL services in the same cable binder.

<span class="mw-page-title-main">ADSL</span> DSL service where downstream bandwidth exceeds upstream bandwidth

Asymmetric digital subscriber line (ADSL) is a type of digital subscriber line (DSL) technology, a data communications technology that enables faster data transmission over copper telephone lines than a conventional voiceband modem can provide. ADSL differs from the less common symmetric digital subscriber line (SDSL). In ADSL, bandwidth and bit rate are said to be asymmetric, meaning greater toward the customer premises (downstream) than the reverse (upstream). Providers usually market ADSL as an Internet access service primarily for downloading content from the Internet, but not for serving content accessed by others.

ITU G.992.4 is a standard for splitterless ADSL2 with data rate mandatory capability reduced to 1.536 Mbit/s downstream and 512 kbit/s upstream. It is also referred to as G.lite.bis.

<span class="mw-page-title-main">G.fast</span> ITU-T Recommendation

G.fast is a digital subscriber line (DSL) protocol standard for local loops shorter than 500 meters, with performance targets between 100 Mbit/s and 1 Gbit/s, depending on loop length. High speeds are only achieved over very short loops. Although G.fast was initially designed for loops shorter than 250 meters, Sckipio in early 2015 demonstrated G.fast delivering speeds over 100 Mbit/s at nearly 500 meters and the EU announced a research project.

References

  1. ↑ "ITU-T Recommendation G.993.1: Very high speed digital subscriber line transceivers (VDSL)" . Retrieved 24 July 2016.
  2. 1 2 3 "ITU-T Recommendation G.993.2: Very high speed digital subscriber line transceivers 2 (VDSL2)" . Retrieved 24 July 2016.
  3. ↑ "VDSL Speed". HowStuffWorks. 21 May 2001.
  4. ↑ "G.993.1 (06/04)". ITU.
  5. 1 2 "New ITU Standard Delivers 10x ADSL Speeds: Vendors applaud landmark agreement on VDSL2". News release. International Telecommunication Union. 27 May 2005. Retrieved 22 September 2011.
  6. ↑ "G.993.2 : Very high speed digital subscriber line transceivers 2 (VDSL2)".
  7. ↑ "Tyrone Fabrication Ltd., Eircom VDSL". Archived from the original on 31 January 2012. Retrieved 8 March 2012.
  8. ↑ Broadband Forum (2016-07-01). "TR-348 Hybrid Access Broadband Network Architecture" (PDF). Retrieved 2018-07-01.
  9. 1 2 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.
  10. ↑ "IT-T xDSLxDSL Standards" (PDF). International Telecommunication Union (ITU). Retrieved 2024-01-08.
  11. ↑ "Very high speed digital subscriber line transceivers". International Telecommunication Union (ITU). Retrieved 2024-01-08.
  12. ↑ "G.993.2 : Very high speed digital subscriber line transceivers 2 (VDSL2)".
  13. ↑ tsbmail (2013-06-14). "G.993.5 : Self-FEXT cancellation (vectoring) for use with VDSL2 transceivers". Itu.int. Retrieved 2013-07-04.
  14. ↑ "The ITU-T's New G.vector Standard Proliferates 100 Mb/s DSL" (PDF). Archived from the original (PDF) on 2018-12-27. Retrieved 2016-07-24.
  15. ↑ "What is VDSL Vectoring, SRA and G.INP ?". www.draytek.co.uk. Retrieved 2021-01-25.
  16. ↑ "Telekom: Magenta Zuhause XL - Alle Tarifdetails auf teltarif.de!". 2020-07-14.
  17. ↑ heise online (2018-08-16). "Supervectoring: Telekom vermarktet VDSL mit 250 Mbit/s" (in German).
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