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Broadband Week for July 12, 1999
AT&T's Salt Lake HFC Trial Seeks More Than Low Costs
By FRED DAWSON July 12, 1999
AT&T Broadband & Internet Services has more up its sleeve than merely another fiber-technology test with the trial of a new hybrid fiber-coaxial design in Salt Lake City this fall.
If all goes according to the expectations of at least some company strategists, the MSO could end up redefining how Internet protocol-based voice and data services are transmitted over cable -- in effect outdating the existing cable-modem standard.
But first, the company will have to demonstrate that the basic HFC design concept -- dubbed "Lightwire" internally and widely known as "mini-fiber node" -- is a practical option, AT&T Broadband spokesman Mark Siegel said.
"This architecture is something we're testing in anticipation that we're going to get millions of subscribers for our advanced services," Siegel said. "If we do, the current architecture -- where 600 households are served from a fiber node -- may not be the best approach. But it remains to be seen whether the new design is the right one."
The Salt Lake City trial, passing 66,000 homes and turning on in October, follows a six-month study of multiple options for improving network performance and capacity through segmentation of nodes. During that time, engineers from AT&T Labs worked closely with the engineering team of the former Tele-Communications Inc., led by chief technical officer Tony Werner.
Based on that study, the company believes it can extend fiber deep enough to eliminate all in-line amplifiers on the coax network, thus reducing serving-area sizes to under 100 households at a cost of $40 per home passed, AT&T Labs district manager Xiaolin Lu said.
Describing the two-phase trial plans in a presentation at the National Show in Chicago last month, Lu predicted that the operational savings from lower power consumption and eliminating or reducing many maintenance procedures needed to keep amplifiers properly tuned would add up to about $11 per home, per year.
These numbers alone, assuming that the cost projections are right, could justify using the approach in systems that have yet to be upgraded to two-way HFC status, AT&T Broadband district manager for product realization Marty Davidson said.
But Lu and Davidson noted that the real payoff on the new design could be the means by which the freed-up bandwidth on the unamplified coax -- adding at least 250 megahertz to the 750 MHz now commonly available -- is put to use in phase two of the trial.
Rather than delivering signals over that spectrum and in the return in traditional modes, the MSO could use time-division multiplexing on an end-to-end basis, allowing each serving area to operate like a local-area network.
"You can use the mini-fiber node to do some local signaling, enabling very low-cost, very simple media-access protocols, versus having to resolve everything back at the headend," Lu said. "You can utilize some kind of Ethernet off-the-shelf product as the cable modem."
Such a capability would eliminate the requirements for the complex media-access control, quality-of-service and other functionalities associated with today's data delivery over HFC, thereby possibly extending the cost justification for the deep fiber deployment to a much broader base of systems, including those already upgraded, Davidson said.
"CPE [customer-premises equipment] is the biggest cost factor in everything, so the payback there could be a major benefit," he noted.
Davidson said the design doesn't require the use of a different fiber strand for every link to the mini-nodes from the fiber multiplexing node.
Options that could be used to allow a single fiber to serve multiple mini-nodes include wavelength-division multiplexing and TDM, with WDM the likely candidate. But Davidson was not certain what the choice was, and other officials could not be reached for answers at press time.
There's also a strong likelihood that new types of integrated optical transmitter/receivers now entering the market for use in fiber-to-the-home applications in Japan and elsewhere could come into play in the new HFC design, Davidson said.
This would greatly reduce the costs of the electronics at each mini-node compared with what the optoelectronic costs at fiber nodes are today.
In order to accomplish the powering of the RF signal at the mini-node across the full range of bandwidth, the system would use new galium-arsenide-based chips, Lu said.
All of this adds up to what appears to be very high costs, notwithstanding AT&T engineers' claims, said a skeptical senior industry engineering executive who asked not to be named.
"Tony Werner says this looks doable, but we've seen a lot of good ideas go up in smoke when it comes to putting them to the test in the field," the executive added.
A case in point was the microcell concept used in conjunction with delivering wireless personal-communications services over cable. "We could just never make those numbers work," the executive said.
Nonetheless, if AT&T is right in its projections, the TDM side of the equation would not seem to present any major technology hurdles, opening the possibility of securing a robust means of delivering voice and data signals that would overcome many of the technical challenges associated with today's cable-modem delivery systems.
The question is whether the TDM approach would generate big savings in terminal gear one year or two from now, when the volume demand for today's cable-data technology will have had a chance to drive down the costs of modems and other devices.
That's a question no one can answer at this point. But it's clear that the cable-technology cost curve has a long way to go before it hits the numbers associated with TDM-based technologies like 10BaseT Ethernet.
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Last Updated: 07/12/99 11:21 AM |
