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Advances spell end to net bottlenecks

Sun, 03/31/1996 - 7:00pm
Fred Dawson

Major advances toward commercialization of cutting edge switching, optoelectronic and millimeter wave technologies are opening the way to an explosion in broadband services to the business community in '97.

At the switching level, manufacturers have begun incorporating newly standardized capabilities into ATM equipment, enabling carriers to move the technology into the core of the telecommunications infrastructure. And on the distribution side, dense wavelength division multiplexing is coming into its own just as regulators are preparing to unleash new classes of wireless transport in the 28-, 38- and 40-GHz regions that are sure to challenge entrenched fiber networks.

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8-Wavelength Laser Array. (Photo courtesy of Bellcore.)

These developments come amid mounting pressure within the business community for extension of the computer revolution to the next level, which means breaking the public network bottleneck to get high-speed data to the desktop at affordable costs. Along with seeking multiprotocol connectivity for LANs and high-speed access to the Internet, business users are also looking for multimedia connections capable of supporting video.

"There's still a cost problem in the consumer market, but, in business, we're getting real customers who see a need for the use of video as part of the information they access from their servers," says Beverly Ulbrich, director of marketing for Sun Microsystems' interactive services group. "Our research shows over 50 million clients (in the client/server computing market) were video ready with decoder technology on board at the end of '95."

Demand for multimedia with video segments is especially strong in the finance and securities industry, where timely information is crucial, Ulbrich notes. In addition, corporate needs for easily distributed worker training materials across all business categories are driving widescale demand for video storage and distribution.

Asynchronous transfer mode

Meeting such demand starts with deployment of ATM (asynchronous transfer mode) switches. "The fulfillment of market demand for multimedia services can't be realized without deployment of a new network infrastructure," says Richard Jalkut, president and group executive of Nynex Telecommunications. "ATM is the only global standard that is capable of integrating local and wide area networks, which is the only way to achieve distribution of computer intelligence throughout the network."

ATM brings flexibility to the core network at a moment when carriers, faced with competition and new applications, must be able to react to churn and new demand quickly, says Randy Carlson, an analyst with The Yankee Group. "Ultimately, carriers are going to want to be able to operate a set of distributed switches in tiers which, from a network management perspective, look like a single switch," he says.

So far, in serving business needs for high-speed data connectivity, LECs have met competition from private networks and competitive access providers by emulating it, using ATM switches at the edge of their networks to port multiple data streams from high-end business customers onto high-speed Sonet links. But ATM has not penetrated into the core of the carriers' networks, nor has ATM network management been integrated into the operating support systems of the larger network environment.

All that is about to change. For example, Nynex has been working with Newbridge Networks Inc., a leading supplier of ATM edge switches, in preparation for deployment of switches in the lower New York LATA by mid-year, with the goal of achieving deployment throughout its territories by 2000, says Edmund Thomas, executive vice president for R&D at Nynex Science and Technology.

Newbridge, which has teamed with Siemens AG to integrate ATM technology into public switched networks, has already begun using the advanced traffic management capabilities in the new 4.0 release of protocols issued in March by the ATM Forum, says Irfa Ali, vice president of marketing at Newbridge. But much work remains to be done.

"Moving deeper into the core of the network, a whole lot of issues need to be addressed," Ali says. "For example, signaling and billing elements of the switched network infrastructure must be incorporated into the new ATM products.

"If you look at the network today, everything is based on SS7 (signaling system 7) switching," Ali adds. "An 800 number is translated into a real number in an SS7 network, and that has to be part of the information carried in the ATM cells."

Newbridge's edge ATM switches currently operate at up to 12.8 Gigabits per second, but the core backbone switches will have to operate at 100 Gbps. Newbridge's switches today can emulate T-1 and T-3 circuits, meaning such links can be routed between different users at different times, but, in the future, the core switches will have to handle DS-0 or individual voice links as well.

A key starting point in the evolution to core ATM switching is to move what is known as multiprotocol over ATM (MPOA) service, now a mainstay of edge switch capabilities, into the public network, which will allow carriers to route data on a switched basis "without using thousands of routers in a given market," as Ali put it. Equally important, the new products will support collaborative computing, tying disparate work stations together on a dialup basis across the wide area.

"This is the beginning of adding individual voice circuits to the ATM network, where voice is imbedded in the multimedia applications," Ali says.

Another important driver behind migration of ATM into the core network promises to be software distribution to computers. "The idea of downloading software cries out for a really good broadband infrastructure," says Thomas Rambold, president of Siemens' Broadband Networks Division.

Dense WDM

With the backbone switching support must come higher capacity in the pipelines to accommodate not only the emerging broadband service demands but also the surging volume in narrowband traffic brought on by PCS and wireline competition. Solutions to this need are racing toward commercialization in wireline and wireless modes in tandem with the '97 timeframe for broadband switching.

On the wireline side, carriers looking for a way to avoid laying more fiber in the wake of a decade of high capital spending have found a solution in dense wave division multiplexing technology, which is the combination of four or more wavelengths of light into a single fiber.

"You're going to see a lot of point-to-point dense wavelength division multiplexing systems (DWDM) going into operation later this year," says Chinlon Lin, director of broadband lightwave systems research at Bell Communications Research. Indeed, MCI has already put a four-wavelength system into operation on a long-haul trunk in the Southeast.

Equally important, Lin notes, optical routing of wavelengths, which avoids costly and time-consuming conversion of signals from photons to electrons and back again, is not far behind in the commercialization process.

"When we get to all-optical networks, we'll see major changes in application of fiber not only in the backbone, but in the distribution loop as well," he says.

What's in store is evident in a new prototype network now operating in the Bay Area of California under sponsorship of the Defense Department's Advanced Research Projects Agency and 10 other entities. Dubbed the "National Transparent Optical Network Testbed" (NTON), the system transmits lightstreams at 2.5 Gbps (OC-48) in multiplexed four- or eight-wave combinations, using an acousto-optical tunable filter switch to route the streams to different points in the network (see Figure 1 and Figure 2).

The NTON, linking University of California at Berkeley and Lawrence Livermore National Lab sites to Pacific Bell and Sprint operating centers, operates over standard imbedded fiber at wavelengths ranging from 1546 to 1560 nanometers, with spacing of two or four nanometers, depending on whether a link operates at 4 or 8 wavelengths per fiber. Signal power is sustained with optical amplifiers, which have been specially conditioned with gain filters supplied by Nortel to maintain uniform ("flat") performance across all wavelengths.

"What we're seeing here is evidence that these types of capabilities are not far from the manufacturing process if the demand for them develops," Lin says.

One of the first commercial applications of all-optical network technology will come not in the U.S. but in the waters around Africa, where a consortium led by AT&T is planning to build a DWDM ring network that will connect individual countries that choose to run fiber to the ring.

"The really significant thing about Africa One (the planned network) is that it will extract each country's traffic optically, which is something that's only been done with prototype networks," Lin says.

Wireless

Coming out of nowhere to challenge wireline operators in the high-speed traffic wars to come are advanced wireless systems operating in the 28-, 38- and 40-GHz spectrum windows. One indication of the role such systems will play can be seen in the land-office business enjoyed by WinStar Communications, a supplier of backbone transport systems which holds licenses for 38 GHz operations in over 40 markets around the country.

The company is providing competitive access providers such as Teleport Communications Group in New York a low-cost means to extend broadband connectivity beyond the reach of imbedded fiber trunk and is lining up customers for backhaul support in the PCS industry, following the path taken by European carriers in PCS facilities interconnections.

"The technology offers a lot of advantages for PCS providers, giving us the opportunity to provide hundreds of low-cost links within the 1,600 square-mile region of an MSA (metropolitan service area)," says David Ackerman, executive vice president of WinStar. Winstar's links typically cost 10 to 15 percent less than those of local exchange carriers for comparable capacity, and they are quicker to implement then traditional microwave links, which typically require long waits for permits at the FCC, Ackerman adds.

Availability of multiple options for backhaul connections is important to the PCS industry, notes Graham Taylor, vice president and general manager for Florida operations at TCG. "Fiber to the base station can be an expensive component of the infrastructure, so it's important to look at more than one supplier," he says.

WinStar, based in New York, is licensed to operate four 100-MHz channels per market in 30 markets, the only 38-GHz carrier with multiple 100-MHz licenses, owing to new FCC rules that limit carriers to one license per market. WinStar obtained most of its licenses under former rules when there was little interest in the spectrum.

Where 38 GHz links were limited to four T-1 channels per 100 MHz of spectrum using four-level frequency shift key modulation, manufacturers are now producing links that can deliver one DS-3 link, or the equivalent of 28 T-1s, per 100 MHz. "Some vendors expect to offer OC-12 (600 Megabits per second) level capacity per 100 MHz within two to three years," Ackerman says.

With such capability will come point-to-multipoint transmission technology, allowing intelligent switching arrays where hubs serve multiple sites with broadband transmission streams. Such advances parallel the growing technical capabilities of other very high frequency transmission systems, including the local multipoint distribution service operating at 28 GHz slated for final authorization at the FCC this month, and for auctioning this summer, and a 40 GHz service class that could be licensed as early as next year.

While LMDS at 28 GHz has been pioneered in the U.S. by CellularVision of New York as a one-way cable distribution service, its real strengths lay in broadband communications, as is evidenced by preparations for service launch in Canada. Last month the government's Industry Canada department promulgated rules for authorizing what it calls "local multipoint communications services" in the 25.35 GHz to 28.35 GHz region, starting with two 500-MHz blocks to be licensed in 66 markets nationwide this summer.

Cable and telephone companies aren't eligible to apply for the first Gigahertz of spectrum but will be allowed to compete in the auctions. Billed as "Canada's third competitive choice," LMCS (local multipoint communications systems) will employ low-power transmitters in combination with small antennas to deliver digital TV, data and voice signals omnidirectionally at distances of up to three miles.

Leading the charge into LMCS is Western International Communications Ltd., a leading terrestrial and satellite broadcast concern based in Vancouver that has been testing the technology for two years. "We intend to apply for licenses in all 66 markets," says Douglas Holtby, WIC president and CEO.

As the only Canadian licensee of CellularVision's technology, WIC has had by far the most experience working with LMCS in Canada. "We have been operating over two (overlapping) cells in Calgary since '94," says John Quigley, vice president of WIC's CellularVision operation. "We're transmitting in FM, omnidirectionally, and have been running digitally the full period."

The company has operated General Instrument's DigiCipher as well as full MPEG-2 successfully, with quadrature phase shift key modulation employed to deliver 38 Megabits per second, or 12 to 16 TV channels in each 20 MHz FM channel, Quigley says. More importantly, he adds, "since April of '95 we've also been operating full duplex T-1 (1.5 Mbps) channels through the system to customer (premises)."

WIC's strategy, reflecting the common carriage requirements of the government's LMCS policy, is to build its business on the interactive digital communications potential of 28 GHz technology. "We're going to move into telecom right off the bat," Holtby says, adding, "I believe broadband data is going to be a much bigger business for us than TV."

WIC has been working with Lockheed-Martin Canada, which has developed a transmitter/receiver that supports a two-way, point-to-point T-1 data stream as well as 200 channels of digital TV, Quigley says. The transceivers, which are small enough to carry with laptop computers and other portable devices, connect over a 10baseT link to the PC, eliminating the need for an external modem.

Quigley says WIC's Calgary cells overlap each other by 50 percent, demonstrating that the CellularVision technology can deliver interactive services using reverse polarization without creating signal interference. The company will use traveling wave tube amplifiers supplied by the Canadian subsidiary of U.S.-based CPI Varian at first, moving to solid-state transmitters once the technology can support a power level of one watt.

WIC, which has been working with a number of manufacturers over the past two years, expects to deploy LMCS systems at the rate of 10–12 cells per month, although this "will be a stretch," Quigley says. "Assuming Industry Canada follows its license schedule this summer, we'd want the equipment to be available to begin deploying cells by the end of the year," he says.

WIC's technical experience offers strong validation to the concept that millimeter wave technology is going to be a major factor in the broadband marketplace, whether for backhaul applications or for delivering multimedia to customer premises. With a number of telcos lining up to bid for LMDS spectrum against CellularVision and other entities in the U.S., it's clear the regional bottleneck will soon be a thing of the past.

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