Very High Speed Digital Subscriber Line
Very High Speed Digital Subscriber Line ( VDSL , the abbreviation VHDSL is considered obsolete) is a DSL technology that delivers significantly higher data transmission rates over conventional telephone lines than, for example, ADSL or ADSL2 + . Like all DSL technologies, VDSL also uses a (twisted) two-core copper line for the last section of the transmission path to the customer , which is routed in the so-called branching cable from the KVz (cable distributor) to the APL (termination point of the line technology).
The International Telecommunication Union (ITU) has currently defined two VDSL standards: VDSL1 ( ITU-T G.993.1 ) and VDSL2 ( ITU-T G.993.2 ).
A number of DSL standards are grouped under the name VDSL.
VDSL1 comprises a number of mutually incompatible DSL technologies. Are typically achieved transmission rates of 52 Mbit / s in the receive direction ( English downstream ) and 11 Mbit / s in the transmission direction ( upstream ). The usable transmission bandwidth decreases with the length of the connection cable. The data transmission rate drops to 26 or 5.5 Mbit / s at a distance of 900 meters from the exchange , and at around 2000 meters you are at ADSL level. For this reason, the distance between the connection of the subscriber terminal and the exchange must not become too great.
In large cities, due to the density of switching centers, most of the population is likely to be covered. In small towns with only one exchange, it will only be enough for VDSL high-speed within a specified radius. Longer distances between the subscriber and the exchange require outdoor DSLAMs . The user-side connections of the exchanges or DSLAMs are often already existing telephone lines. The network-side connections of the exchanges or DSLAMs are usually fiber optic cables.
In addition to the Internet connection, VDSL1 is also occasionally used to extend or couple Ethernet networks via existing copper wire pairs. Also known in this application under the name 10BaseS ( Infineon ), sold u. a. by Cisco as Long Reach Ethernet (LRE).
The VDSL1 standard has not been able to establish itself on a large scale worldwide. This can be related to the fact that VDSL1 DSLAMs only have a short signal range and there are no options to prioritize certain applications during their transmission, which is mandatory for the simultaneous transmission of Internet and IPTV services. VDSL1 has only achieved greater distribution with several million lines in South Korea , Japan , the USA and the People's Republic of China . In South Korea, a nearly area-wide VDSL1 network was set up. In the USA, Qwest, Verizon ( FiOS ) and AT&T ( U-Verse ) offer their services on different bases: U-Verse is a "Fiber to the Node" ( FTTN ) offer that is very similar to VDSL in Germany. Verizon offers FiOS via "Fiber to the Home" (FTTH), which brings the fiber directly into the house and thus can cover much longer distances from the distribution box, but is also much more expensive to install the cables to the end user. As in Germany, there are so far only a few metropolitan regions FTTN or FTTH offers, as the costs for the installation are very high. In contrast to Germany, the monthly costs for FTTN / FTTH are often lower, on average US $ 29.25 for a 30/5 Mbit line.
VDSL2 is based on the Discrete Multitone (DMT) transmission method and offers theoretically achievable combined data transmission rates of up to 350 Mbit / s (upstream + downstream) at limit frequencies of up to 35 MHz, with a very short cable route. Thereafter, the theoretically achievable combined speed drops to 100 Mbit / s at a distance of 500 m and 50 Mbit / s at 1000 m. After a distance of approx. 1600 m, the data transmission rates are comparable to those of ADSL2 +. The VDSL2 standard was adopted by the International Telecommunication Union (ITU) in spring 2005 . The standard itself is based on the tried and tested ADSL2 + standard and is fully downward compatible with it. However, instead of up to 480 (512 - 32) carriers in the downstream with the various ADSL variants, considerably more carriers are used, which are distributed between upstream and downstream depending on the band plan. The crosstalk that occurs between several VDSL lines at higher frequencies has been minimized in most of the band plans (14.5 dBm compared to 20.5 dBm) due to the lower power compared to ADSL. In addition, options have been implemented to realize several virtual connections at the same time via a physical connection in order to be able to prioritize IPTV data.
VDSL and its successor standard VDSL2 were developed with the aim of being able to offer so-called “ triple play services ”. This is to be understood as the merging of classic telephony services in the form of analog / ISDN or IP telephony , broadband Internet and IPTV.
The VDSL2 standard provides eight different " profiles " as a major innovation . In the profiles, among other things, the respective cut-off frequency, the carrier distance and the generated signal strength are specified. The different parameters for the individual profiles are the reason that the maximum achievable data transmission rates vary from profile to profile. Another ninth profile, the VDSL2 profile 35b, was re-standardized by the ITU in ITU-T G.993.2 Annex Q in January 2015. Depending on the manufacturer, it is also referred to as super vectoring or vectoring plus (V plus).
( MHz )
directional 1 )
1 bidirectional data transfer rate means the transfer rate from the upstream plus that from the downstream . The division of this bandwidth into upstream and downstream depends on the profile used, the band plan and the annex .
In addition to the profile, a band plan must be specified, which regulates the interleaving of the individual upstream and downstream channels as well as keeping any frequency bands that may still be used for POTS or ISDN free . There are different band plans for North American, European and Asian networks. The PSD mask ( Power Spectral Density ) is closely linked to the band plan . This mask limits the transmission power of the VDSL2 modem on certain frequencies. The main aim is to ensure the "peaceful" coexistence of ADSL, ADSL2, ADSL2 + and VDSL2. The standard also provides for attenuating certain frequency ranges below the level of −80 dBm / Hz in order to protect the frequency bands for amateur radio between 1.8 and 29.7 MHz. The network operators select one or more profiles, a band plan approved according to the feed point and a profile for a PSD mask for the respective port.
VDSL in Europe
Based on the VDSL2 chipset Vinax of Lantiq builds German Telekom since the spring of 2006, a VDSL2-based distribution network on. The progress and experiences with a network of this size are being observed with great interest by many foreign network operators, as they are also planning to set up VDSL2-based networks. The data transmission rate provided by VDSL2 is sufficient to provide triple play offers. With the help of VDSL2 as the transmission method, these enable Internet data , Internet telephony and television programs (IPTV) to be transmitted in HDTV quality. As with ADSL connections, classic landline telephony is transmitted on the same line in a different frequency range. In order to prevent mutual interference of the fixed line telephony and the VDSL signals, VDSL2 splitters were used on the customer and network operator side. Telekom is now converting its (V) -DSL connections to VoIP, so that the use of a splitter is no longer necessary. New extensions from around the end of 2013 therefore no longer have the option of making connections via the newly extended outdoor DSLAMs with ISDN / POTS. Among other things, this means that certain business customer tariffs cannot be booked in these areas. The declared goal of Telekom is to convert all old VDSL outdoor DSLAMs that still have splitters to VoIP technology by the end of 2018 [obsolete] in order to activate vectoring. Connections based on “indoor” VDSL will not be able to receive vectoring until further notice.
Since October 17, 2006, Deutsche Telekom AG has been offering VDSL2 connections in its T-Home fixed-line network in the twelve largest German metropolitan areas, with around 35 other cities originally to follow by the end of 2007. In addition, VDSL2-based products can now also be used in many smaller cities and communities. In these expansion areas, however, the expensive FTTN expansion with outdoor DSLAMs will not be required for the time being . Only the main distribution locations are equipped with indoor VDSL2 DSLAMs and connected to the IPTV concentration network, so that a considerable number of subscribers there do not have the VDSL2 and ADSL2 + profiles marketed by Telekom at the time due to the high line attenuation of longer connection lines and the triple-play offers based on it. As part of T-Home's new strategy of offering IPTV services in urban areas without outdoor DSLAM expansion since August 6, 2007, the main distributors (local exchanges) in many other cities were equipped with IPTV DSLAM line cards and connected to Connected to the IPTV concentration network ("Indoor VDSL2 DSLAM expansion") Within a radius of up to 1 km from the main distributor, subscribers in these cities can book IPTV packages from T-Home on a VDSL2 basis, within a radius of a little IPTV packets based on ADSL2 + are marketed over 1.5 km around the main distribution frames connected to the IPTV network . A far-reaching VDSL2 expansion in the entire city area using outdoor DSLAMs was not initially planned, with the exception of the 50 T-Home Entertain cities. Currently (as of 2013/2014), Telekom is increasingly equipping some access areas with outdoor DSLAMs at its own expense.
Since the amendment to the Telecommunications Act (TKG), Deutsche Telekom's VDSL internet access has been exempt from market regulation . However, this still depends on whether the new subscriber line transmission technology is classified as a “new market” by the Federal Network Agency as the competent regulatory authority . The amendment was passed on November 30, 2006 by the Bundestag and on December 15, 2006 by the Bundesrat. The European Commission (EU Commission) decided on June 27, 2007 to sue Germany for breach of contract for this reason. The law is also controversial within Germany. The parliamentary opposition and Deutsche Telekom's competitors have already made critical comments. Although, strictly speaking, the law applies to the entire telecommunications sector, it is only conceivable to apply it to Deutsche Telekom in the foreseeable future, which is why the law is also known as "Lex Telekom".
From June 4 to June 30, 2009 and since September 2009, VDSL can also be used at Telekom without IPTV , i. H. can be ordered as a double-play offer for Internet and telephony, by telephone and online. At the beginning this was only possible online. The first such connections were made in August 2009. The first telecommunications resellers who build on broadband wholesale services from Deutsche Telekom have already included VDSL2-based products in their offerings. 1 & 1 has been offering the service since September 2009 . Since September 8, 2009, Telekom has again been able to order VDSL 25 and VDSL 50 as the “Call & Surf Comfort VDSL” tariff combination, ie without bundling with the Entertain packages (IPTV).
But also providers such as Vodafone , O2 , DNS.net, 1 & 1 and Congstar and some local providers, such as B. wilhelm.tel and willy.tel in Hamburg offer VDSL2 in Germany. It can be used in the regions in which Telekom has already expanded the local network.
Outdoor DSLAM expansion in large metropolitan areas
Since spring 2006, the cable distributors have been built over with outdoor DSLAMs (→ illustration). In general, with the help of the cable distributors, the purely passive, i. H. Currentless operated distributors are the last meters of the connection cable from the exchange to the respective customer connections in the houses or apartments. Depending on the local conditions, the previous cable distributors have now been replaced by the new, much larger multifunctional housings or the new housings have been installed in the immediate vicinity of the existing cable distributors. The multifunctional housing contains, among other things, the new VDSL2 hardware (DSLAMs, line cards , splitters ) with the associated power supply and active cooling. The copper connection cables , electricity and fiber optic cables , which provide the connection to the Internet backbone and the IPTV services, are fed in via conduits from the ground . An outdoor DSLAM can serve up to 408 customer connections (" ports ") depending on the expansion level . Expansions are usually possible when there is greater demand; in most cases, additional reserve glass fibers were laid as part of the expansion , which can be put into operation if required.
As part of the expansion, not all of the cable distributors were built over, of which there are several thousand in larger cities. A certain number of cable distributors that have not been built over are connected to the new DSLAMs using so-called "cross cables", that is, conventional copper cable bundles usually a few hundred meters long. Customers who are connected to these non-built-up cable distributors can usually also receive the new high-speed connections, although the cross-cable connection also increases the distance and thus the total cable length to the DSLAM, which can have a negative effect on the maximum speed that can be achieved.
As an alternative, there is a supply of VDSL2-based services through so-called "in-house DSLAMs", which are located directly in the local exchange , for customers whose connection is in the immediate vicinity of a local exchange.
According to the current state of knowledge, Deutsche Telekom only uses the profiles “17a ” and “35b”, previously also “ 8b ”, when the customer connection is short from the in-house / outdoor DSLAM . Depending on the speed to be achieved, the maximum distance between DSLAM and customer connection is around 550 to 850 meters, according to Telekom. Connections with asymmetrical transmission speeds of 25/5 Mbit / s and 50/10 Mbit / s (downstream / upstream) were offered in Telekom's VDSL2 network . The condition of the copper lines must be taken into account, e.g. B. the wire cross-section, the presence of stub lines, corrosion, et cetera. These parameters influence the maximum speed that can be achieved.
The aim of the expansion in the large metropolitan areas is to position the DSLAMs as close as possible to the connection points in the apartments. These outdoor DSLAMs are themselves connected to a GbE aggregation switch via a Gigabit Ethernet cable . From here, the traffic is fed to the BRAS (and above it to the IP backbone) and the IPTV service platform via further aggregation levels. However, the last few meters from the DSLAM to the customer connection are bridged by the classic copper cable, as has been the case up to now. This type of network expansion is known under the name “ FTTN ” (“Fiber To The Node”, “Glass fiber to the distributor”; outdated term: FTTC , “Fiber to the Curb”, “Glass fiber to the curb”). Each time the VDSL2 modem is synchronized, higher or lower speeds can be achieved within the defined data rate corridor , depending on the current line status . As a rule, however, the VDSL2 DSLAMs are located sufficiently close to the respective building transfer points so that, under normal circumstances, relatively high speeds can be achieved at the upper end of the corridor.
With VDSL2 vectoring (G.993.5) it is possible to provide speeds of up to 100 Mbit / s in the downstream and up to 40 Mbit / s in the upstream for a larger number of customers than before. On the basis of ongoing measurements of the interference signals and compensation for these, the influence of crosstalk can be reduced. On December 19, 2012, Deutsche Telekom submitted an application to the Federal Network Agency for a regulatory order for VDSL2 vectoring. On April 9, 2013, the approval process was successfully concluded with a preliminary decision, so that the expansion could begin. In spring 2014, VDSL2 vectoring was tested in pilot operation in the 06122 area code (parts of Hofheim am Taunus and Wiesbaden ). Vectoring has been used in the first areas since August 28, 2014.
In Austria, VDSL2 has been offered by A1 (then Telekom Austria) since November 2009 under the name A1 Glasfaser Power (formerly Gigaspeed ). Rural areas in particular are connected first, as alternatives are already available in the larger cities. Up to 100 Mbit / s receive rate (“download”) and up to 20 Mbit / s send rate (“upload”) are offered. As a rule, however, depending on the line quality, only significantly lower bandwidths are achieved.
Since September 2010, alternative operators have also been able to offer VDSL2 to their customers via the switching center (VDSL @ CO). As of September 2010, Silver Server was the first alternative provider for VDSL2 in Vienna and Linz.
The outdoor DSLAMs from A1 (formerly Telekom Austria) are referred to as Access Remote Unit (abbr. ARU), these can be recognized by the fact that "ARxxxx" (xxxx = unique identifier) is written on the top right of the door. These ARUs are connected with fiber optics (→ FTTC ).
In Luxembourg, VDSL2 has been offered by Post Luxembourg with FTTH under the name "LuxFibre" since October 2011 . Here, FTTN and FTTH are marketed together, which is not always obvious to the consumer.
Swisscom has been the only provider to operate a national VDSL2 network since 2006. At the beginning, VDSL was only offered to operate the IPTV service Swisscom TV (then Bluewin TV). It was only a few months later that customers were able to obtain an Internet service on a VDSL basis. The network has been continuously expanded since then and still has a very large coverage and port density. Both Huawei and Alcatel Lucent DSLAMs are in use. Since the beginning of the expansion, the FTTN concept has been followed and thousands of district distributors have been built and rebuilt. Since the end of 2013, Swisscom has been building DSLAMs even closer to end customers in order to shorten the copper cable lengths even more. For this purpose, the FTTS concept is implemented and the small, waterproof DSLAMs micro-CANs are installed underground in the cable ducts. This shortens the cable lengths from the DSLAM to the end customer modem to less than 200 m. Huawei supplies the equipment for this. Swisscom prefers VDSL for all IP-based services and also migrates existing ADSL connections if possible. Bit rates of up to 100 Mbit / s downstream and 25 Mbit / s upstream are currently being switched, mainly rate adaptive . Spectrum profiles 8b, 12a and 17a are used depending on the cable length.
In the UK, the largest provider of VDSL is the BT Group . The company initiated a test phase for VDSL in Muswell Hill , north London , using FTTC technology. The test phase was successful, which is why deliveries began under the NGA (Next Generation Access) banner in selected locations in Great Britain. Originally, Telecom offered 40 Mbit / s receive and 10 Mbit / s transmission rate with the new technology, depending on the distance from the respective DSLAM. However, from 2012 onwards, data transfer speeds were doubled. In addition to this development, further tests are being carried out with FTTP technology (Fiber to the Premises), which, although more expensive and complex to implement, can deliver reception rates of up to 110 Mbit / s and which is assumed to be more future-proof than FTTC. In the meantime, this process has been improved to a maximum of 330 Mbit / s receive rate and 30 Mbit / s send rate. British Telecom has not been the only provider of VDSL since 2011. Other small providers (such as Rutland telecom, ask4 or Ripwire) offer VDSL services with regional coverage. The technology used here corresponds to FTTC (Fiber to the curb), with the last section running over existing wiring.
VDSL in North America
In the United States of America there are several providers that are not limited to individual regions or states. Numerous regional providers are also available. CenturyLink provides FTTN VDSL to Denver , Salt Lake City , Boise , Phoenix , Seattle , Omaha , Minneapolis , Des Moines , Las Vegas , Fayetteville, and the areas surrounding these cities. The rate structure of Centurylink reaches 40 Mbit / s in the downstream and 20 Mbit / s in the upstream (status: 2013).
AT&T is a provider of Internet and television services via VDSL in some regions under the brand name U-verse. The services are based on FTTN, although FTTP is used in some areas.
Verizon is the provider of the FiOS product in some major cities and offers up to 300 Mbit / s in the downstream. The service is based on FTTP and usually CAT5e Ethernet (or MoCA ) is used to distribute the data service in the house. However, this is also practiced in apartment buildings, where the connection via CAT5e or Coax is often not expedient for individual users.
In the urban areas, VDSL is offered by MTS in Manitoba , SaskTel in Saskatchewan , Lightspeed, WestNet and Nucleus in Alberta and British Columbia , Bell Internet, Nexicom, Acanac and TekSavvy in Ontario, and Bell Internet and Telus in Québec .
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