DSL

Next Generation DSL

Elastic Networks, formerly part of Nortel Networks, unveils EtherLoop, combining the best of Ethernet and DSL. It may enable speeds of up to 10Mbps.

by Jim Thompson

When Phil Griffith, vice president of marketing for Elastic Networks, told me they could provide high-speed data over existing copper lines, I paid little attention. Hey, that's not new, that's DSL. When he explained he was talking about 4-Mbps speeds in both directions, over virtually any, non-conditioned copper phone line at distances up to 21,000 feet, he got my attention.

EtherLoop, or second-generation DSL as its also called, provides a solution to many of the problems of conventional DSL technology. It is, in essence, a blending of DSL and Ethernet, combining the high data rates of DSL and the half-duplex communications model of Ethernet. The "burst" packet delivery capabilities of the technology minimizes many of the more serious side effects of conventional DSL services.

Compatible With Other Services
ISPs will be happy to learn that with EtherLoop there is little or no interference from reflections caused by poor quality wiring often found in the cable bundle. This includes wire gage changes, bridge taps, loading coils , and cross-talk. As a result, it's compatible, and doesn't interfere with other services such as ISDN, ADSL, G.Lite, HDSL, SDSL, and T-1 in the cable bundle.

"With current DSL technology, its very often necessary to check the copper, one pair at a time, to see if it can sustain a DSL signal," said Phil Griffith. "If the pair has bridge taps or wire gauge changes, the technician may have to find another pair or engineer that pair and remove the taps and wire gauge changes. This technology can sustain bridge taps and wire gage changes. You don't need a 'conditioned' line."

EtherLoop has a good deal of intelligence built-in. Signal quality is continually monitored. Using continuous rate adaptation techniques, internal frequencies of the attached modem are changed to reduce crosstalk and avoid interference with other lines and services in the cable bundle.

Higher Speeds
EtherLoop uses a range of frequencies from roughly 30-Khz up to approximately 3-Mhz, divided up into 10 overlapping frequency spectrums. The lowest spectrum has a total frequency range of 62.5 kilohertz. The highest has a frequency range of 1.667 megahertz. This gives EtherLoop a theoretical maximum symbol rate of 1.667 megasymbols per second or a speed of 1.667 megabits per second. In much the same way that analog modems use signaling techniques, EtherLoop uses QPSK (Quadrature Phased Shift Keying) and QAM (Quadrature Amplitude Modulation) to increase the transmission rate.

According to Elastic Networks, "QPSK manipulates the phase of the wave, supporting waves that start 90 degrees out of phase. It also allows the "height" of the wave to operate at two levels, the maximum, and 1/2 of the maximum. With the combination of these two techniques, there are now 4 different 'positions' that each hertz can be in. Four positions represent two bits log₂(4), which would allow a 1.667 megasymbols per second signal to represent 3.33 megabits per second."

By adding QAM, different degrees of phase and additional levels of amplitude are added to the mix. The concept is that 16 QAM (Quadrature Amplitude Modulation) provides 4 different heights, and 4 different phases, for a total of 16 positions, which then generates 4 bits per Hertz (log₂(16)). "This would allow a 1.667 megasymbol-per-second signal to represent 6.667 megabits per second. 64 QAM supports 8 different heights and 8 different phases, for 64 positions, which generates 6 bits per Hertz (log₂(64)), which represents 10 megabits per second," notes a white paper from Elastic Networks.

What it means is higher speeds. Currently, EtherLoop provides up to 4-Mbps adaptive throughput in both directions at distances up to 21,000 feet. Elastic Networks plans to offer speeds of 6-Mbps in the third or fourth quarter of this year and 10-Mbps sometime in 2001.

Ethernet Kinship
To the typical LAN, EtherLoop looks like Ethernet. Basically, it follows, as much as possible, the Ethernet IEEE 802.3 standard with a few improvements. The point-to-point configuration of EtherLoop means its configured in a "master/slave" arrangement which overcomes the typical collision problems faced by Ethernet. The lower quality of the subscriber local loop is overcome with frame error checking and retransmission using Ethernet checksum. Since it interfaces with Ethernet without any protocol conversions, time, trouble and money are saved.

Of course, this isn't Ethernet so, although it runs over longer loops of lower quality, the peak bandwidth is lower. It's also appropriate only in a point-to-point link and it's more expensive than Ethernet.

Those offering the EtherLoop service say, for them, the best part is the ease of deployment. "We covered over 20 percent of our dial-up customers in six weeks," said Ron Hinds, director of marketing for Grand River Mutual Telephone Corp. in Princeton, Missouri. "More importantly, we installed 90 percent of the customers without a truck roll. Of that amount, 72 percent were able to do the complete installation themselves. From that perspective, it was definitely a success." Hinds added that they have "not had any of the noise issues" between cable pairs that is normally associated with typical DSL products.

As any ISP or CLEC, fewer truck rolls and lower costs per line means greater revenue. "There are a number benefits for the ISP," noted Griffith. "If I have a choice of buying a $30 per month conditioned data pair verses an $8 per month regular copper pair, there is no question which is best for me," Griffith said. "Lower line costs can make a big difference."

Customer Benefits
For customers, there are a number of very real benefits. In addition to the higher speeds than are typically offered via traditional DSL, users can also simultaneously access both voice and data services over the same line. This, combined with the ease of installation makes the technology ideal for use in apartment buildings and hotels. According to Griffith, EtherLoop is also competitively priced, at about $49 per month.

Elastic Networks is a spin-out of Nortel Networks and offers service to a number of ISPs, including Darwin Networks, which provides service in 1,400 hotels properties across the nation, US OnLine, which consists of more than 100 ISPs nationwide, and Oregon Trail Internet, Inc. Elastic recently inked a deal with New T&T in Hong Kong.

To demonstrate the capabilities of EtherLoop DSL, Elastics Networks has a program called speed-up America. The program is highlighted by a mobile van, equipped with everything needed to run EtherLoop DSL that simulates an actual installation. It includes everything from the DSLAM to the equipment found at the customer location. I was especially impressed with the streaming audio and video and the video conferencing demonstrations when I visited the van during Internet World in Los Angeles.

The speed-up AMERICA van will be at the following locations:

• June 4-8 SuperComm Atlanta, Georgia
• July 16-18 2000xDSL ConForum Chicago, Illinois
• September 17 NTCA Fall Conference Nashville, Tennessee
• October 1 USTA Miami, Florida November 8-10 ISPCon Fall Orlando, Florida

Related Articles
A detailed discussion of tariffs of conditioned vs. unconditioned pairs is included in the article,
"Roll Your Own DSL Connection?"

A recent US Online press release announced a deal with Elastic.

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