Making DSL go for the long run

New algorithms extending technology's reach One of the biggest knocks against DSL is its inability to provide high-speed access service beyond 18,000 feet (and in some cases beyond 12,000 feet). Not a problem if the intent is to serve a dense area where central offices are nearby.

But getting DSL to mass-market acceptance means hitting the suburban and more remote areas with longer loop lengths. Just as important is addressing the huge market served by digital loop carriers (DLCs), a technology that limits the choices of potential high-speed users.

During the last month, two vendors announced development systems and sub-systems that will extend DSL's reach. Both will compete with companies such as Alcatel, which uses some sub-systems to move beyond 18,000 feet, and Marconi, which announced during Supercomm this June in Atlanta that it created a DSL-capable DLC.

Lucent Technologies' entry into the market is a new remote terminal as part of its Stinger line of DSL access concentrators. The Stinger remote terminals essentially are hardened and scaled-down versions of the company's CO-based Stingers. Lucent anticipates the remote terminals being deployed only by incumbent carriers until regulators allow competitive local exchange carriers to co-locate equipment in remote terminals.

"This enables the carrier to address a base of customers that they couldn't previously get to," said Bruce Miller, senior product manager for Lucent's MultiDSL group.

Using the remote terminal, carriers can reach most of the market that resides beyond 16,000 feet. In addition, the company has developed a scheme whereby remote terminals can be deployed in conjunction with DLCs. This includes a separate cabinet for DLC locations. And while that carries an extra space requirement, it doesn't require major changes to the network. "We're relying on the ability to not have to retrofit," Miller said.

At the same time, the company will support single-line high bit-rate DSL (SHDSL) or G.shdsl in its Stinger line once the standard is ratified by various standards organizations. Ratification for SHDSL, which lets carriers deploy symmetric services ranging from 192 kb/s to 2.32 Mb/s over a single copper pair, is expected by the International Telecommunication Union in February.

"We're actually shipping today with HDSL-2, and when the standard is complete, we can do a software upgrade to SHDSL," Miller said.

Lucent already announced two customers for the remote terminal-CoServ, a utility company based in Corinth, Texas, that also provides telecom service, and QS Communications, a German DSL provider.

Traditional DSL vendors aren't the only ones pushing the distance limitation. About six months ago, Symmetricom introduced its GoLong loop extender, which acts as a filter/signal regenerator. At last month's ISPCon in San Jose, the company said its solution made it through independent lab testing that verified its ability to provide speeds up to 1.5 Mb/s downstream and 128 kb/s upstream.

Unlike other extenders that act more as signal regenerators, GoLong is a filter that only takes the DSL signal and re-amplifies it while passing through all other transmissions after about 9000 feet of copper. In very long loops, a second repeater is used.

According to company estimates, carriers that can reach up to 30,000 feet can address about 95% of the potential high-speed Internet customers in the U.S.

Symmetricom currently quotes carriers a price of $500 per user in quantities of 12, though a single user would cost closer to $1000. With an installed cost of a DSL access multiplexer and modem at around $600 per user, the company is banking on carriers analyzing the additional bandwidth for incremental investment, Dropping said.

However, Miller said, the more important element of any DSL extension technology is the ability to conform with standards. "Most of those technologies are proprietary, so some people will buy it, but it's not going to be mainstream," Miller said.