The Alcatel Experience of DSL Deployment
`
`Dr Bob Sutherland, Alcatel
`
`Incumbent telcos desire to make the optimum use of their existing copper pair networks in order to
`deliver the new services required by their customers. This enables the incumbent telcos to compete with
`new operators who use alternative technologies, without incurring the very high costs of building new
`infrastructure. The technologies used by the new operators include cable TV systems, which can be
`extended to offer not only broadcast TV, but also telephony, fast internet access and other data services,
`as well as video on demand. Other competing technologies are satellite, which can be combined with a
`telephony back channel to provide a limited interactive service, radio microwave distribution, and all fibre
`systems. However, the price performance combination of the DSL technologies is so attractive that even
`new operators are increasingly making use of them.
`
`There is now a range of different DSL technologies available for high speed transmission over copper,
`which are appropriate to the requirements of different customers. These include HDSL and SDSL for
`symmetric services mainly to business customers, ADSL for asymmetric services to residential and
`SOHO customers, and VDSL for very high-rate symmetric or asymmetric services to business or
`residential customers. VDSL has a relatively short range, and is thus often operated from street
`cabinets, although operation from exchange buildings is sometimes done. HDSL, SDSL, and ADSL can
`be operated from exchange buildings or street cabinets as appropriate. This paper outlines the range
`Alcatel DSL products, and the experience of their deployment.
`
`Alcatel experience of DSL began in 1989 with field trials of 281 Q transmission. The FONT AS product
`{later known as ASMLX) resulted in 1990, and was widely deployed in Germany (about 12,000 systems).
`FONTAS/ASMLX was a uni-directional product, requiring separate pairs for each direction of
`transmission.
`
`Later developments utilised bi-directional transmission on each pair. Two pairs were used in the US, but
`sometimes three in Europe due to the requirement for 2 Mbit/s rather than 1.5 Mbit/s. Howevt:1r, in some
`European countries use of three pairs was difficult due to the cable being quad based, and all more
`recent European systems use two pairs only. Rate adaptive (nx64kbit/s) versions are available to
`provide a trade-off between data-rate and range. Alcatel 1512 HDSL is deployed world-wide (about
`130,000 systems).
`
`Enhanced HDSL began with ANSI HDSL-2 in the US, a single pair system for a fixed rate of 1.5 Mbit/s
`(approved for publication in December 1999). A rate-adaptive version of the standard is under
`development in ITU-T, named SHDSL. In Europe ETSI are working to define ETSI-SDSL, which will be
`a single pair standard, closely aligned with ITU-SHDSL, including rate adaptation and in-band ISDN
`amongst other features. Alcatel Line-Runner products are available to these standards.
`
`Alcatel field trials of ADSL were followed by the first significant deployment in Singapore in 1997. At
`present Alcatel have about 50% of the DSLAM market, with over 1.3 million lines installed world-wide.
`ADSL line cards are also offered in the Litespan 2000 range in the USA, and will be offered in the
`Litespan 1540 range in Europe and elsewhere. In addition, the Alcatel ADSL chip-set is used in the
`products of many other manufacturers. Alcatel DSLAMs and chip sets use the standardised DMT line
`code.
`
`All Alcatel ADSL DSLAMs and customer end modems are in fact multi-standard, so that they will operate
`with not only with full-rate ADSL (G.DMT), but also with reduced rate ADSL (G.Lite), as well as with
`ANSI Tl413-1998. Interoperability between equipment from the various manufacturers of ADSL is of
`importance, in particular where the customer purchases his own modem and the operator wishes to
`avoid a truck-roll. Alcatel believe that in this case it is often better to use full rate ADSL with a distributed
`splitter, rather than G.Lite. Alcatel organise comprehensive testing at our interoperability laboratories in
`Antwerp, the University of New Hampshire in the US, and in Taiwan.
`
`© 2000 The Institution of Electrical Engineers.
`Printed and published by the IEE, Savoy Place, London WC2R 0BL, UK.
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`Authorized licensed use limited to: Christine Dimitrov. Downloaded on April 07,2022 at 20:05:20 UTC from IEEE Xplore. Restrictions apply.
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`IPR2022-00833
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`VDSL is currently under development by Alcatel. Alcatel believe that DMT is the most appropriate line
`code for VDSL, for reasons of performance, flexibility, compatibility with other service in the same cable
`and with wireless communications systems, future proofing, and interoperability with ADSL. The DMT
`TDD R1 .0 system was demonstrated at Geneva in 1999, and is available for laboratory and field trials ..
`The DMT FDD R2.0 product is currently under development, and this will feature a high degree of
`integration as well as low power. Interoperability between different manufacturers of VDSL is also of
`importance.
`
`The deployment of the various DSL technologies has raised a number of questions, many concerned
`with the interaction between these technologies.
`
`Multiple systems of the same DSL technology interfere with each other when operated in the same
`physical cable. For HDSL and other echo-cancelled systems the main limitation is Near End Cross Talk
`(NEXT), and the worst case effect of this can be predicted by using the ETSI noise model.
`
`There is also interference between different DSL technologies operated in the same physical cable.
`Again the main component is NEXT, but this could be eliminated if it could be ensured that the up and
`downstream transmisison frequency bands did not. However, this is not done, and for example, the main
`limitation on ADSL in the UK is probably is NEXT from HDSL systems. In the US repeatered T1 systems
`may be of more concern.
`
`Some Telcos have a requirement to provide the same customer with both ISDN and ADSL. In this case
`Jhe ADSL frequency range can be altered so that it does not overlap with that of ISDN. However, there
`is then a reduced bit-rate, and the ISDN (G.DMT Annexe B) and normal versions of ADSL (G.DMT
`Annexe A) would interfere with each other if deployed in the same cable. Countries with a high IDSN
`pe11etration, for example Germany, do use the ISDN version. An alternative approach would be to carry
`the equivalent of the ISDN traffic within the ADSL bit-stream itself.
`
`External interference also plays a part, but the DMT standard adopted for ADSL is often an effective
`solution. Carrier tones subject to severe interference, for example from broadcast radio or from radio
`amateurs, can simply not be used to carry data. Interference can also occur from non-radio systems, for
`example the Home Phone Networking Alliance (HPNA) systems for data distribution within the home.
`Signals from HPNA systems will be transmitted out into the telephony access cables, and cross talk will
`then cause interference with DSL signals in other pairs in the cable. The frequencies used by HPNA are
`such that, without precautions, VDSL would be the most affected. To avoid such interference, the HPNA
`signals in-house could be blocked at the entrance of the home by appropriate filters to avoid pollution of
`the outside loop plant. Alternatively, careful frequency planning for VDSL, possibly in combination with
`HPNA cross-talk cancellation techniques, can solve the problem.
`
`DSL can also cause interference with radio systems. Again, the use of DMT provides the possibility of
`not using particular tones likely to cause interference. In the UK the Radio Communications Agency
`have issued a draft proposal for radio emissions, and a similar proposal has been made in Germany by
`Reg TP. The radio emissions are increased if the pair is unbalanced. There may thus be increased
`radio emissions when the DSL signals traverse the customer's home wiring, which may not be
`·
`adequately balanced.
`
`For all DSL systems there is a trade-off of range and bit-rate. If service is offered at fixed bit-rates then
`there are customers who will be unable to receive service. This problem can be mitigated by the use of
`rate adaptive DSL systems. On training up after connection the DSL system will determine the bit-rate
`that it can achieve with the required margin. A remaining issue is that subsequently to installation the
`performance may be degraded because of additional interference, from newly installed DSL systems or
`from external sources of interference. In this case the bit-rate available to the customer will be reduced.
`
`There are obviously circumstances where rate adaptive systems are not appropriate, such as the use of
`ADSL for video on demand, where a minimum bit-rate of about 2 Mbit/s is normally required. In this case
`a prediction is required of those customers in range of the service, and this can be made from a line test
`of loop resistance, or from a calculation based on the cable details.
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`IPR2022-00833
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`In the case of HDSL the standards do not provide for interoperability, that is an exchange unit from one
`manufacturer will not work with a customer premises unit from a different manufacturer. For ADSL it is
`the intention that equipment from different manufacturers should be mixed, and to this end trials have
`been held by Alcatel and others. In some cases a feature may be available from one manufacture and
`not the other, in which case a lowest common denominator approach has to be taken,
`
`As noted above, interoperability is particularly vital where the operator wishes to avoid a truck-roll
`(distributed splitter full-rate ADSL or G.Lite, or splitterless G.Lite). If the customer is free to purchase his
`equipment from whichever manufacturer he chooses, then the telecoms operator will not know the
`characteristics of the customer end equipment, and there may be an impact on performance. The use of
`distributed splitters rather than a splitterless system, will usually provide improved performance (a high
`pass filter is installed in the DSL modem connection, and a low pass filter in each phone connection). It
`should be possible for the customer to install these distributed filters himself, and thus a truck-roll should
`still not be required. In this case full rate ADSL may be used instead of G.Lite.
`
`The availability of DSL raises a large number of marketing issues, which are not the prime concern of
`this paper. These include service cannibalisation, that is should an incumbent operator introduce new
`DSL based services even if these lead to a reduction in revenue from his existing services, or should he
`wait until a competitive operator is ready to strike? DSL connection to the Internet offers the possibility to
`replace time based charging, but should this be by usage based or flat rate charging? Note also that the
`service from ADSL lines will not be the same for all customers, unless a very low bit-rate is specified.
`The concept of universal service may thus be undermined in those countries in which it is usual.
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`Authorized licensed use limited to: Christine Dimitrov. Downloaded on April 07,2022 at 20:05:20 UTC from IEEE Xplore. Restrictions apply.
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`IPR2022-00833
`CommScope, Inc. Exhibit 1016
`Page 3 of 3
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