Here's a good article about Elastic's technology:
eetimes.com
Copper proposals tout Ethernet versus ADSL
By Craig Matsumoto
EE Times
(07/26/01, 3:01 p.m. EST)
SAN MATEO, Calif. — Among the ideas being floated in the 802.3ah task force is a technology constructed to combat the vagaries of DSL connections. Elastic Networks Inc. (Alpharetta, Ga.) is pitching its100BaseCu as a way to get more bandwidth out of an Ethernet connection across old twisted-pair cables.
100BaseCu can shift a call to different frequencies to avoid crosstalk and other interference. Elastic is touting that adaptability as an advantage over ADSL, which operates at a fixed frequency.
"Because of the loop robustness, being able to deal with bridge taps and so forth, it's much more tolerant," said David Kaufman, executive director of business development for Elastic. "It falls in the same sort of category as DSL but it solves some of the [deployment] problems."
The 100BaseCu technology is the second generation of the company's Etherloop technology, originally developed at Nortel Networks. Unlike ADSL, which transmits a constant bit rate, Etherloop operates in burst mode, transmitting only when there's data to be sent.
During the pauses, Etherloop tests the strength of the signal. If it's unacceptable, the signal is shifted to one of 12 available frequencies, depending on which has the highest available bandwidth.
The correction process happens continually to combat sporadic line noise. "You want technology that reacts real-time to changes in the environment," Kaufman said.
100BaseCU uses frequencies in a higher range than Etherloop, matching the frequency range proposed for Ethernet over VDSL, and will use broader frequency bands as well, allowing for transmission speeds up to 100 Mbits/second, Kaufman said.
Like DSL, 100BaseCU uses modems at the customer premises and the central office, connected by extant telephone lines. The customer modem would be plugged into an Ethernet device such as a cable modem or a PC, while the head-end modem would connect to a service provider's Ethernet network or even the Internet.
100BaseCU has a reach of 21,000 feet, on par with the best ADSL implementations but outpacing the 4,000-foot reach of VDSL, which could be a key factor in mass deployment of Ethernet to the home, Kaufman said.
"What they're going for is a very high-bandwidth, relatively short-reach technology," Kaufman said of VDSL. "If you truly want to address the broad market that's addressed by copper plant that's buried today, you really have to go out to about 13,000 feet," he said, citing a Telcordia study.
Of course, that factor won't come into play if Ethernet in the first mile ends up targeting offices more than homes, because VDSL should be a suitable technology for serving multitenant office buildings, Kaufman said. "That's one of the things the standards group has to work on — what markets are the drivers are trying to serve?," he said.
In addition, 100BaseCU would have the appeal of being a purely Ethernet play, Kaufman said. "Some of the others are more like taking an ATM technology and moving it to an Ethernet world," he said. |
