SDSL: Schwing both ways

Telecom will this year introduce its next DSL technology - SDSL (Symmetrical Digital Subscriber Line), which promises speeds of up to 2Mbit/s in each direction.

Telecom will this year introduce its next DSL technology - SDSL (Symmetrical Digital Subscriber Line), which promises speeds of up to 2Mbit/s in each direction.

Further out, it is examining the emerging VDSL, which is designed to use relatively short runs of copper - about 300 metres - to deliver up to 50Mbit/s.

DSL technologies use conventional copper wiring to deliver high-speed data services. As its name suggests, the Asymmetrical Digital Subscriber Line (ADSL) technology on which Telecom's JetStream service is based, is faster one way than the other; up to 4Mbit/s downstream and 640k on the return path.

Daniel Omundsen, Telecom's manager, technical solutions, says SDSL has just been through a standardisation process that should unite "a whole bunch of flavours" of the technology.

"What the industry has settled on is one called SHDSL, which is a standards-compliant version. The standard was ratified about a month ago and we're expecting commercial supply of equipment to become practical within a couple of months."

While ADSL has been tagged as a downstream-oriented internet access product, SDSL is more likely to be used in frame relay and IP networking services - typically providing connectivity between branches of a business, or between companies that need to exchange large chunks of data, such as publishers and print houses.

It will see some older frame relay equipment retired and would take the place of DDS lines, but Omundsen can't venture an opinion on whether that means better pricing

"It would make it easier for us to continue to reduce the price, but until we've got the technology in the networks and seen what it's going to cost us, it's hard to say."

While SDSL is imminent, VDSL is "further down the track" he says.

"It's one of those technologies that's sitting there and looks on paper to have some real benefits, but the equipment's still at a very early prototype stage."

Omundsen says VDSL could potentially be a technology installed in cabinets at the edge of Telecom's fibre network. Users within about 300 metres from the cabinet - say, on an industrial estate - would have access to bandwidth of about 50Mbit/s.

"The question then is what kind of service are you going to deliver. What are people going to use it for?"

Omundsen says there is also potential for ADSL equipment to be installed in cabinets in residential areas where the copper run from the local exchange is too long to allow DSL to function - if there's a business case.

The three DSLs are likely to represent Telecom's future technology choices for its copper network.

"They cover the spectrum of what's able to be run on copper right now," says Omundsen. "You can choose between either running lots of one bandwidth in one direction and a small amount in the other, or having it symmetrical. And the only other thing you can do beyond that is try and shorten up the loop and make the speed higher."

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