VDSL2 vectoring

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VDSL2 vectoring is an extension of VDSL2 that is intended to reduce unwanted crosstalk between neighboring metallic subscriber lines . As a result, the transmission rate , especially in unshielded cable bundles of conventional telephone networks and with many VDSL subscribers, can in some cases be increased significantly. The procedure is standardized by the ITU-T under the designation G.993.5 .

General

Main cable with 1200 and 2000 twin wires

In the case of data transmission, the limiting factors for the available transmission rate are mainly the line attenuation and crosstalk. While the attenuation is mainly given by the line length, the crosstalk depends on which signals from neighboring lines influence each other. Up to a few thousand subscriber connection lines are spatially closely combined in main cables . Due to the structure of the cable, mutual crosstalk is promoted. The individual subscriber lines in such a cable are usually used independently of one another for different purposes by different access providers. Examples are data access via ADSL , VDSL or voice services such as ISDN or POTS .

With VDSL2 vectoring in the central DSLAM on the supplier side and in the VDSL2 vectoring modem on the customer side, mutual interference between neighboring transmission lines is reduced by means of a special channel coding . In order to do this, it is technically necessary for the DSLAM to have complete control over all individual lines in a main cable harness, so that mutual compensation can take place. The DSLAM knows at all times which signal is present on which line. In this way, he can reduce the mutual interference using a method similar to echo cancellation .

Since, according to the current state of the art, when using VDSL2 vectoring, the DSLAM must have complete control over all subscriber lines in a cable bundle, the company that wants to use vectoring must also have access to all copper wire pairs on the cable distributor (KVz). Problems can arise from " unbundling " (e.g. the use of the "last mile or meter" to the customer by different providers): With unbundling, subscriber lines are made available to different access providers, each with their own and independent devices which means that mutual interference signal reduction with VDSL2 vectoring is no longer possible.

Vectoring also plays an elementary role in the successor standard G.fast .

Procedure

With VDSL2 vectoring, mutual crosstalk in the uplink and downlink is compensated. The method is designed to compensate for the crosstalk at the line end, it is the technical term English crosstalk far-end , called FEXT. The DSLAM modifies its transmission signal in the downlink as part of the channel coding in such a way that the data stream at the customer-side cable end has the lowest possible interference from other signal lines. In the process analogous to this, compensation takes place in the uplink from the VDSL2 modem to the DSLAM.

Since the crosstalk depends on physical effects of the line, such as capacitive coupling, and cannot be avoided due to the principle involved, the expected interference at the transmitter is estimated, and in the constellation diagram the transmit symbols on the complex level are opposite to the expected interference in the case of the quadrature amplitude modulation used postponed.

To estimate the variable and mutually different levels of interference on a specific line, the information from the adjacent channel lines on the DSLAM is required. In addition, individual transmission channels are used in the context of discrete multitone modulation for ongoing interference signal measurement with known pilot data sequences. In the context of the process, return channel information about interference from the remote station is available if it supports vectoring.

The standard distinguishes between the following characteristics, depending on the level of information available for determining disturbance variables, with the quality of the disturbance suppression decreasing from top to bottom:

Characteristic Explanation
vectoring-capable The customer's VDSL2 modem is vectoring-capable and interacts optimally with the DSLAM
vectoring-friendly The customer's VDSL2 modem is not capable of vectoring, but it only interferes to a small extent with the other participants
alien Any DSL modem does not interact with the DSLAM using VDSL2 and disrupts the VDSL2 vectoring process on neighboring lines

Development in Germany

In 2012, Deutsche Telekom announced that it would offer bandwidths of up to 100 Mbit / s in the downstream and up to 40 Mbit / s in the upstream in Germany in the future based on vectoring and FTTC . (previously VDSL2 without vectoring: up to 50 Mbit / s in the downstream and up to 10 Mbit / s in the upstream)

According to a draft decision of the Federal Network Agency in April 2013, the Telekom should give its competitors access to future local loop grant in principle continue. Under certain conditions, however, it could also refuse it so that it itself or a competitor could use vectoring there. The prerequisite is that there is already a second landline network operated by a competitor in the area. In August 2013, the final approval for vectoring use in Germany took place; the EU Commission had previously approved a second draft decision by the Federal Network Agency from July of that year.

In mid-2015, the EU Commission blocked the state funding planned by Germany for vectoring because it hindered competition.

Despite protests from Telekom competitors, among other things because of a lack of procedural transparency, the Federal Network Agency again allowed Telekom to expand vectoring technology in 2016. In return, Telekom committed itself to providing all households in the local area with high-speed broadband connections and made an investment commitment. Messrs. EWE TEL ( Oldenburg ) announced immediate action before the administrative court in Cologne on, was dismissed on March 17, 2017. However, an appeal to the Federal Administrative Court was approved. The industry associations Federal Association of Broadband Communication , Buglas ( Federal Association of Fiber Optic Connections . EV ) and VATM ( Association of Providers of Telecommunications and Value-Added Services ) jointly declared that the regulatory authority's decision would offer Telekom an extensive vectoring expansion monopoly in the almost 8,000 local areas and user benefits is far too low because less than four percent of all landline connections are now supplied with 50 Mbit / s. Significantly more and better quality would be e.g. B. to achieve with targeted funding.

criticism

Baden-Württemberg's consumer protection minister, Alexander Bonde , primarily criticizes the exclusion of competitors associated with the use of the technology. In addition, the relatively small increase in performance compared to conventional VDSL2 (maximum doubling of the capacity from 50 to 70 or approx. 90, if available, to approx. 180 Mbit / s) only applies to approximately the first 600 m line length; the cost-benefit ratio is more than doubtful compared to increased expansion and the use of fiber optic technology . The economic researchers at the Ifo Institute for Economic Research do not share this criticism.

Alternatives

The G.hn transmission method originally developed by the ITU for home network cabling enables data transmission rates of up to 1.5 Gbit / s and offers the advantage that the respective signal adapts to the carrier medium used, i.e. it can handle different types of lines.

Instead of waiting for the supply by a provider, z. B. Local authorities or districts are responsible for laying fiber optic cables ; they currently (autumn 2016) perform up to 100 gigabits / second. In the course of intermunicipal cooperation and for organizational or administrative and economic reasons, they may set up a “ special purpose association for broadband supply”.

In mid-2016, American scientists presented a method with which the capacity of fiber optic cables could be doubled: with the help of a kind of “ frequency comb ”, signals could be transmitted over several thousand kilometers without a repeater. The technology should be ready for series production from around 2020. Other market-ready alternatives based on the telephone cable are supervectoring and G.Fast .

DSL pioneer John Cioffi has developed a transmission technology that makes it possible to transmit one terabit per second over 100 m of copper cable. Here, the air gap between the copper cable is used so that high-frequency signals between 100 gigahertz and 300 gigahertz can be transmitted via one shaft. The developer Cioffi also calls this technology TDSL.

Web links

Individual evidence

  1. ↑ G.993.5: Self-FEXT cancellation (vectoring) for use with VDSL2 transceivers. Retrieved January 17, 2013 .
  2. ↑ a b Federal Network Agency gives the green light for VDSL vectoring . In: tarifetarife.de . August 29, 2013. Retrieved August 29, 2013.
  3. ↑ Jan Rähm : Copper forever. In: Deutschlandfunk , Computer und Kommunikation , December 5, 2015, accessed on October 9, 2016
  4. ↑ telekom.com: Vectoring: Boost for broadband expansion in Germany. ( Memento of the original from July 7, 2014 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. In: Telekom.com , Medien , October 9, 2016 @1@ 2Template: Webachiv / IABot / www.telekom.com
  5. ↑ "Federal Network Agency regulates broadband expansion with VDSL2 and vectoring". In: spiegel.de , April 9, 2013
  6. ↑ EU does not allow funding for vectoring in Germany. In: golem.de , June 16, 2015, accessed October 9, 2016
  7. ↑ Karl-Heinz Neumann in conversation with Manfred Kloiber : Trouble about the vectoring decision. In: deutschlandfunk.de , Computer und Kommunikation , November 28, 2015, accessed on October 9, 2016
  8. ↑ Philipp Banse: Outrage over Telecom license. In: deutschlandfunk.de , Wirtschaft und Gesellschaft , April 7, 2016, accessed on October 9, 2016
  9. ↑ See Dieter Nürnberger: Telekom at IFA - Fast Internet and mobile TV. In: deutschlandfunk.de , September 2, 2016, accessed on October 9, 2016
  10. ↑ Telekom is allowed to expand: VG Köln dismisses action against vectoring decision from March 17, 2017
  11. ↑ Network agency: Telekom is allowed to make the Internet faster. In: badische-zeitung.de , September 3, 2016, accessed on October 9, 2016
  12. ↑ See also: Jan Rähm: Broadband expansion - The struggle of Telekom for the copper network. In: deutschlandfunk.de , background , June 8, 2016, accessed on October 9, 2016
  13. ↑ See also: Jan Rähm in conversation with Manfred Kloiber: Fiber optic expansion: VDSL vectoring and other regulatory problems. In: deutschlandfunk.de , Computer und Kommunikation , April 23, 2016, accessed on October 9, 2016
  14. ↑ Vectoring = cementation of copper monopoly & prevention of glass fiber. In: golem.de , April 10, 2016, accessed October 9, 2016
  15. ↑ Sabine Model: "I feel kidding". In: badische-zeitung.de , August 24, 2016, accessed on October 9, 2016
  16. ↑ Ifo Institute is skeptical about the accelerated expansion of the fast Internet in Germany
  17. ↑ Jan Rähm: The new old transmission standard offers a way out. In: deutschlandfunk.de , Computer und Kommunikation , April 23, 2016, accessed on October 9, 2016
  18. ↑ Astrid Wulf: Dig yourself for fast internet. In: deutschlandfunk.de , Germany today , April 16, 2014, accessed on October 9, 2016
  19. ↑ Manfred Frietsch: Much speaks in favor of a district network. In: badische-zeitung.de , September 29, 2016, accessed on October 9, 2016
  20. ↑ a b Frank Grotelüschen: Capacity of light guides - fleet of fibers on the march. In: deutschlandfunk.de , Forschung aktuell , June 28, 2016, accessed on October 9, 2016
  21. ^ Daniel Gramespacher: District of Lörrach: Expansion of fast internet is making progress. In: badische-zeitung.de , December 16, 2016, accessed on December 17, 2016
  22. ↑ TDSL: 1 TBit / s over the copper cable