SuperComm 96 sparks lively interest in dense WDM

Aug 1st, 1996

SuperComm `96 sparks lively interest in dense WDM

GEORGE KOTELLY

In addition to shattering records in attendance (38,169) and number of exhibitors (638) in Dallas last June, the SuperComm `96 telecommunications trade show served as the arena for raising the bar on gigabit-transmission capacities over existing fiber-optic networks using dense wavelength-division multiplexing (WDM) technology. Focusing on the expected needs of telecommunications carriers for expanded fiber capacity to deliver future multimedia services, several vendors of dense WDM systems, such as Ciena Corp., Pirelli Telecom Systems Group and Alcatel Telecom, presented products that "high-jumped" over current 4 and 8 channels of 2.5-Gbit/sec transmissions to new levels of 16, 32 and 40 channels of 2.5- and 10-Gbit/sec transmissions.

Before the show officially opened, John Ryan, a principal in Ryan, Hankin and Kent Inc., a San Francisco-based communications and photonics consulting and research firm, homed in on attendee interest in dense WDM through his primer session "Fiber networks--what are the options?" Ryan discussed the emergence, timeliness and merits of WDM and photonics as key enabling technologies. He said, "WDM is starting to mature, and new systems are using dense WDM." Ryan also predicted that fiber-to-the-home networks using a photonic transport layer would be available in three to five years.

Increased bandwidth capacity

To maintain leadership positions, telecommunications carriers are exploring dense WDM technology as a means of increasing bandwidth capacity on existing fiber, thereby eliminating the need to deploy more fiber. In many existing installations, they have exhausted their fiber bandwidth with current communications services and are, therefore, seeking more bandwidth for the anticipated delivery of interactive multimedia services. By multiplexing a higher number of communications channels--for example, 32 or 40 rather than 4, 8 or 16--over longer distances, carriers would save network costs because they would increase capacity by factors of 8 to 40 without the need for additional fiber, implement fewer optical amplifiers and leverage initial investments.

ElectroniCast Corp., a San Mateo, CA-based fiber optics market-research firm, predicts explosive growth in the dense WDM component market during the next 10 years as telephone companies, cable-TV operators and other carriers seek ways to maximize network capacity over optical-fiber links. Jeff Montgomery, company chairman, estimates that worldwide consumption of dense WDM components will surge from $100 million in 1995 to $10.5 billion in 2005, with half the sales occurring in North America.

He forecasts, "Several component technologies have advanced to the point where dense WDM networks are now the clear economics-based solutions in some networks, such as in undersea cable and long-haul terrestrial networks involving spans of hundreds of kilometers. As WDM component technology continues to advance and per-gigabit-kilometer costs drop, WDM will increasingly be applied to shorter- distance links."

On the show floor, Ciena Corp. in Savage, MD, dramatically raised the dense WDM capacity level by describing a pace-setting 40-channel system for its MultiWave 1600 product line. The high-capacity system is expected to multiplex 40 2.5-Gbit/sec OC-48 channels for an aggregate capacity of 100 Gbits/sec over a distance of 600 km on a single fiber using a line amplifier at about every 120 km.

"Our technology, including precision optical sources, narrowband optical filtering and ultraflat optical amplifiers, enables us to provide 40-channel dense WDM systems with extremely narrow channel spacing," says Steve Chaddick, Ciena vice president for product development.

Company officials also described an optical add/drop multiplexer that lets one to several OC-48 channels be dropped and added along a route while the remaining channels proceed in an express format. This amplifier eliminates the need to terminate the entire optical layer at an intermediate site where a fraction of the total payload is needed. Standard Synchronous Optical Network (Sonet) optical interfaces terminate the optical spans at each end, reflecting an open system at the photonic layer.

Announced earlier in June and demonstrated in its exhibitor booth, Ciena reported that long-distance carrier Sprint has deployed the company`s 40-Gbit/sec, 16-channel OC-48 dense WDM system along a 200-mile route in the Midwest and in other Sprint network routes. The system allows Sprint to increase its fiber-network capacity by a factor of 16, without installing more fiber-optic cable.

The 16-channel wavelengths range from 1557.36 to 1545.32 nm. Each channel runs bit-rate transparent from 150 Mbits/sec to 2.5 Gbits/sec, functions within existing Sonet/Synchronous Digital Hierarchy asynchronous line terminal equipment, provides integrated network management over a separate optical-service channel and operates over a conventional nondispersion-shifted fiber pair. Sprint is currently operating 4- and 8-channel WDM equipment.

Mark Lutkowitz, president of Trans- Formation Inc., a telecommunications transmission equipment market research consultancy in Birmingham, AL, advises, "There will be tremendous worldwide growth in WDM systems that will continue into the twenty-first century because current, relatively inexpensive semiconductor lasers in fiber-optic transport systems cannot be extended far enough to meet even [today`s] capacity needs. Given the limitations on today`s technology, it is likely that the maximum capacity on a commercially available time-division multiplexer will remain at 10 Gbits/sec for at least 10 to 15 years. Interexchange carriers will be the main buyers of WDM in the short term, as they desperately need solutions that will give them greater capacity on the limited number of fibers in their networks.

"Ciena has designed a smart strategy of focusing its efforts on establishing a strong presence at Sprint, an aggressive deployer of WDM systems. Shipments to a large carrier give newcomer Ciena credibility as a viable player and should lead to contracts with other users. It is [likely] that one of the Sonet transport vendors will team up with Ciena to provide a more complete package that will include maintenance and operational advantages."

Another leading player in dense WDM technology is Pirelli Telecom Systems Group, which announced that its 32-channel, OC-48, 80-Gbit/sec, WaveMux 3200 system would be available in early 1997. If desired, the system could also be used to mix and match OC-48 and OC-192 channels. The system uses the 1530- to 1560-nm optical transmission window, network management and planning software, add/drop capabilities at the optical level, and optical amplification technology to extend the distance between transport nodes to 1200 km. In the Pirelli system, 16 amplifiers are needed over 1200 km, whereas 64 amplifiers would be needed for an 8-channel system.

"Pirelli helps to end capacity constraints for all of today`s voice, data, image and video networks," said Mehmet Balos, vice president for marketing, sales and business development at Pirelli. "The industry`s capacity-demand models show a doubling of WDM capacity requirements every year. That includes corporate enterprise networks, the Internet, online service networks, medical networks and cellular network backbones."

According to Fahri Diner, manager of digital transport products at Pirelli, "We are jumping from 8 wavelengths to 32 wavelengths [instead of] going to 16 for several reasons. One is because the customer capacity demand for oncoming services is already there. Historically, in the Sonet world, customers have quadrupled their network capacity demands; they jumped from OC-3 to OC-12, then OC-12 to OC-48, and now OC-48 to OC-192. That is why this system handles OC-192 as well as OC-48.

"Another reason is economic justification. It does not cost twice as much to build a 32-channel optical amplifier as it does a 16-channel one. More important than providing increased network capacity from point to point, though, is providing network solutions, such as flexibility in network optical add/drop capabilities, easily moving information around and readily changing the structure of the network," maintains Diner.

Paul Shumate, executive director of broadband local access and premises networks at Bellcore, a communications research company in Morristown, NJ, who also spoke at the fiber-optic primer session, said, "Ciena Corp. and Pirelli pushed the capabilities of commercial WDM products another step at SuperComm. Ciena introduced its 16-wavelength MultiWave 1600 system, which achieves 40-Gbit/sec throughput at 2.5 Gbits/sec per wavelength, and Pirelli described its forthcoming WaveMux 3200 system, which combines 32 channels to achieve 80-Gbit/sec throughput.

"Whereas [WDM] systems already available and installed in backbone networks have spaced wavelengths 3 to 4 nm apart, these latest products follow the ITU [International Telecommunication Union] guidelines of an 0.8-nm spacing. The narrow spacing allows the composite spectrum to be amplified easily for long-span applications. Such dense WDM technologies are the enablers of multiwavelength networks," he noted. Shumate also stated that fiber-to-the-home networks were making good progress--especially overseas--and were the best long-term solution (see page 52).

A new height in gigabit-transmission capacity at 160 Gbits/sec has been accomplished by Alcatel Telecom by combining its Alcatel 16192 SM 10-Gbit/sec Sonet multiplexer and its 16-channel WDM technology. "This bandwidth," cites Joe Bass, Alcatel Telecom vice president and general manager of lightwave products, "means greater, faster and more-efficient services, particularly in the video and ATM [Asynchronous Transfer Mode] areas." For perspective, a 160-Gbit/sec transmission rate, which is 64 times faster than a 2.5-Gbit/sec rate, permits the simultaneous transmission of two million telephone conversations or, alternatively, 64,000 television channels.

The 160-Gbit/sec transmission rate is obtained by using WDM technology for 16 optical carriers running at 10 Gbits/sec instead of the current commercial rate of 2.5 Gbits/sec. The 16 different wavelengths are transmitted and propagated simultaneously over a single fiber using Alcatel 1610 OA fluoride-based optical amplifiers, which provide higher signal-to-noise ratios across a wider bandwidth than do silica-based amplifiers. q

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