DSML3 vendors promise to triple VDSL2’s reach

Equipment vendors Actelis Networks and ECI Telecom say they’ve completed the first successful tests of a technology that could triple the reach of VDSL2 and in some cases reduce the number of remote terminals needed to serve customers by 90%.

The iSmart Consortium, which includes Actelis and ECI, say three tier-one carriers have now tested their digital spectrum management level-three (DSML3) technology for reducing crosstalk in DSL networks, though members won’t name the carriers or identify the continent where the tests took place.

Actelis and ECI first started talking about DSML3 back in 2006. At the time, ECI had even been calling it VDSL3, though Actelis isn’t using that name now. DSM is already used to reduce interference and crosstalk in DSL networks in two ways: reducing impulse noise (like the sudden turning on of a nearby vacuum cleaner) and spectrum-balancing (carving out spectrum for each user). iSmart has been focusing on a third method called vectoring, which employs multiple input/multiple output technology. Essentially, vectoring “learns” how crosstalk occurs within binder groups and uses that information in real time to coordinate DSL signal transmissions so that they cancel out each other’s crosstalk, improving the performance of the networks. In particular, the technology is helpful in reducing far-end crosstalk, or FEXT – the crosstalk that occurs at the far end of last-mile copper loops.

“The improvement of DSML3 is most pronounced where FEXT is stronger, on short loops,” said Ioannis Kanellakopoulos, Actelis’s chief technology officer. Whereas VDSL2 might typically be used today to deliver 50-Mb/s over 1,000 feet, he said, “With DSML3, you’ll be able to get it at almost 3,000 feet. Maybe 2,700. But if you go pretty far out in loop length, you’re not going to get much [improvement] from vectoring because FEXT is not a significant contributor on long loops.”

For that reason, DSML3 is drawing a lot of interest in Europe, said Erik Keith, an analyst with Current Analysis. "Loops are shorter in most of Europe, and unbundling regulations [and] requirements make [fiber-to-the-home] buildouts very unappealing," he said.

Theoretically, Actelis said, DSML3 could be used with VDSL2 line-bonding – another long-discussed method for increasing VDSL’s rate/reach ratio, and one that introduces crosstalk concerns – to get even more performance out of copper networks.

The iSmart Consortium is hoping to see the ITU finalize the DSML3 standard – nicknamed G.Vectoring – in October. Commercial equipment could be available next year, Actelis said, though the timing of those products would depend on customer demand.