Device Doubles DSL Distance

Network-enhancement solution provider Symmetricom this week begins field trials of a loop extender system that promises to stretch the viable range of ADSL service to as much as six miles from CO.

by Jim Thompson
[December 20, 2000]

Utilizing a filtered/amplification technology, San Jose, Calif.-based Symmetricom Inc. has launched a full-scale test of a system that, reportedly, extends the range of conventional ADSL lines by roughly a factor of two.

"Our GoLong loop extender solution allows an ADSL network to deliver data speeds of 1.5-Mbps downstream and 128-Kbps upstream at distances of up to 30,000 feet," said Don Skipwith, vice president of Business development at Symmetricom.

Real-world conditions
The GoLong service has already been tested and confirmed by an independent testing laboratory and will undergo field trials by Chester Telephone Company in Chester, South Carolina from December 18, 2000 to January, 2001.

Chester Telephone Company signed onto the trial program in the hopes of resolving the difficulties it's had in reaching customers with ADSL services. The independent phone company, which operates in the rural midlands of South Carolina, serves an area of approximately 750 square miles and 18,000 customers. Approximately 125 of these customers are currently DSL subscribers.

Finessing the broadband divide
Assuming the field trial validates the earlier lab testing, it will signal a great leap forward for DSL technology. Under conventional ADSL technology, performance and data rates drop off significantly at distances of around 13,000 to 14,000 feet (less than three miles) from the central office (CO). Conventional ADSL doesn't work at all at distances of more than 18,000 feet from the CO.

"We say that's just not fair," commented Skipwith. "It's created broadband 'haves' and 'have nots.' That's what we are addressing with GoLong. With our system, a CLEC or ILEC can provide premium ADSL service to anyone within six miles of the CO, which is about 95 percent of the population."

Like conventional ADSL, Go Long technology can deliver speeds up to 6-Mbps downstream at a distance of 9,000 feet or less, but it provides for consistently higher speeds as the length of the loop is extended. For example, at 18,000 feet, the cut-off length for conventional service, GoLong can deliver data at speeds of more than 4-Mbps. At distances of up to 21,000 feet, only one repeater is needed. Two repeaters further extend the range from 21,000 to 30,000 feet.

Skipwith noted that DSL is actually a broadband signal that's split into many different frequencies or, as he called them 'buckets.' Many of these buckets are related to the downstream signal a smaller number are dedicated to the upstream signal. "What we do is to split the signal and then amplify the downstream separate from amplifying the upstream, then we put them back together," he said. "It's a filtered/amplification system that we are using. Best of all, it's also a standard, not a proprietary technology."

Speed is in the details
GoLong actually inserts an active element, or repeater, into the loop plant. It's deployed on a single circuit basis with an Office Repeater Bay (ALE-C) card as well as an ADSL loop extender (ALE-R) card. According to Symmetricom, the ALE-C card fits into standard telephony office repeater bay equipment such as 3192 mechanics. The repeater is deployed in existing 439 telephony outside-plant mechanics.

"We've built in technology where we power this mid-span repeater from our central office card which also can talk to the repeaters to check their health," added Skipwith. "We can tell if there's a problem with the span line, the cable itself, or the repeater."

Another promising aspect of GoLong is that it's compatible with most existing equipment. "We have validated that GoLong can coexist with non-repeated ADSL living within the bounds of spectrum management class 5 (SMC 5) power spectral density, as defined by the industry standards committee T1E1.4," said Barry Dropping, Symmetricom's GoLong director of engineering who added that it works with standard DMT DSLAM equipment.

Trucks, humans will be required
While it may extend the reach of ADSL, GoLong does nothing to eliminate the dreaded 'truck roll' or service call needed for installation of the service. "It doesn't change any of the current install procedures of DSL," declared Skipwith. "With our technology, to boost the distance, you do have to boost the signal. So a truck roll is needed to install a loop extender, mid-span."

The actual cost of installing the GoLong technology is, according to Symmetricom, "about the same" as what it currently costs for conventional ADSL. In the words of Skipwith, "the cost of DSL service is normally in the range of about $700 per subscriber. This figure includes the modem and the portion of the DSLAM that is used for the individual service. Our installed cost should be around that same $700 mark initially and it will go substantially below that as we get into volume."

Extending the reach of ADSL to 30,000 feet, or six miles, will certainly provide a significant boost to the popularity and deployment of ADSL service. It would also bring broadband data access to many of rural, exurban, and even suburban areas that have been bypassed by the high-speed highway.

—End