Vendors Closing in on 1G Bps Using DSL

DSL vendors are using a variety of methods such as bonding several copper lines, creating virtual ones and using advanced noise cancellation to increase broadband over copper to several hundred megabits per second.

At the Broadband World Forum in Paris, Nokia Siemens Networks became the latest vendor to brag about its copper prowess. It can now transmit speeds of up to 825M bps over a distance of 400 meters, it said on Monday.

However, the company isn't alone in wanting to tell about the kind of speeds next-generation DSL (Digital Subscriber Line) systems can achieve. Last week, Huawei said it can transmit 700M bps over the same distance. Today, Alcatel-Lucent said it has achieved 910M bps in its latest round of tests over 400 meters, according to a spokesman.

To boost DSL to those kinds of speeds, the vendors are using a number of technologies. One way is to send traffic using VDSL2 (Very high bit-rate Digital Subscriber Line) over several copper pairs at the same time, compared to traditional DSL which only uses one copper pair. This method then uses a technology -- called DSL Phantom Mode by Alcatel-Lucent and Phantom DSL by Nokia Siemens -- that can create a third virtual copper pair that sends data over a combination of two physical pairs.

However, the use of these technologies also creates crosstalk, a form of noise that degrades the signal quality and decreases the bandwidth. To counteract that, vendors are using a noise canceling technology called vectoring. It works the same way as noise-canceling headphones, continuously analyzing the noise conditions on the copper cables, and then creates a new signal to cancel it out, according to Alcatel-Lucent.

To get really high speeds vendors are using four copper pairs, which will not be readily available among broadband operators. A more realistic scenario is using two copper pairs, which can still boost the bandwidth to 390M bps over 400 meters, according to the latest tests done by Alcatel-Lucent. In general, vectoring can bring significant advantages at distances up to 1,000 meters, Alcatel-Lucen said.

ZTE is taking an even more cautious approach, and said on Friday it can reach 100M bps using VDSL2, vectoring and one copper pair over 300 meters.

Products are now entering field trials and operators will be able to start using them in commercial services during next year.

Copper is still the most common way of carrying fixed broadband, with a share of about 65 percent, compared to 20 percent for cable and 12 percent for fiber, according to market research company Point Topic.

Fiber all the way to the home is the ideal long-term solution for fast broadband, but the new technologies will help operators offer faster speeds using copper as fiber coverage is expanded over the coming decades, vendors agree.

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