DSL acceleration

Stephen Wilso/Informa Telecoms & Media
On the face of it, DSL acceleration technologies seem to offer a neat solution to a key problem of fixed line operators: to offer superfast broadband without having to invest billions rolling fiber all the way to the home. But the new DSL technologies, as discussed in last week’s DSL Acceleration conference, are not without their own complexities.
 
Vectoring promises to allow operators to boost the speed and reach of their copper-based broadband networks by eliminating a kind of interference between VDSL2 lines, known as “cross talk”. But eliminating this cross talk leads to further challenges. For example, once the cross talk has been eliminated further impulse noises will be revealed that were previously masked by the crosstalk. About 85% of the revealed noises will be from within the subscriber’s home. This will necessitate improvements in so-called dynamic spectrum management (DSM) Level 1 technology (also known as dynamic line management) which aims to keep lines stable and without resynchs that lead to customer downtime and irate calls to customer service centers.
 
Although ADSL from the central office and VDSL2 from the cabinet would not cause terminal problems for vectoring, with ZTE claiming losses from optimal vectoring gains of around 10% thanks to their use of upstream back off power, there will be problems with VDSL2 from the incumbent and sub loop unbundling. Many of the delegates seemed skeptical that sub loop unbundling requirements would be lifted, although this has already occurred in Belgium.
 
In addition, operators seemed skeptical on the realism of deploying vectoring in the very short term because of the lack of commercial rollouts. Availability of chipsets will need to improve with Ikanos currently refining their vectoring technology. Alcatel Lucent will use its own chipsets but will need to perform more field trials for its first commercial vectoring customer, Belgacom, before the operator can launch.
 
There will also be elements of vendor lock-in with the technology. For example, an operator need only replace its VDSL2 line cards in order to support vectoring – provided the cards are from the same vendor of the DSLAM. In order to use a rival vendors’ vectoring technology, the operator would have to replace the whole DSLAM including shelves and cabling. To some extent this could increase prices as there would not be a level playing field between competing vendors. Interoperability between different vendors’ chipsets on the DSLAM and customer premise equipment (CPE) sides will also not be available initially, again increasing the risks of vendor lock-in.
 
Despite these constraints I am still of the opinion that vectoring is a very promising technology and one that operators would be wise to examine very carefully.
 

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