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WDM Makes Waves
Carriers all over the world look to catch the wavelength by adding to their existing fiber
Frank Barbetta, Contributing Writer
Wavelength-division multiplexing (WDM), once considered just another transport technology, is fast becoming the heart and soul of the global telecommunications infrastructure. Carriers worldwide are deploying WDM like never before, as emerging higher-capacity WDM technology-80 wavelengths with 10-Gbit/s channels-makes its way into the market.
WDM isn't new in carrier networks. But its popularity is on the rise because of increased traffic demands, mostly due to the Internet. Carriers are looking to WDM as a cost-effective way to increase bandwidth without laying new fiber optic cabling for point-to-point traffic. WDM fragments a single strand of fiber into different wavelengths that provide multiple channels of multigigabit speeds.
North American long-distance providers such as AT&T, Sprint Corp., MCI WorldCom Inc. and other regional and newcomer carriers, are adding WDM to their fiber optic plants. Global Crossing Ltd. (Hamilton, Bermuda) is building WDM into its new transoceanic submarine cable network, and BT and other carriers in Europe are building pan-European lightwave networks with WDM.
And in the United States, incumbent local service providers like Bell Atlantic Corp. are considering WDM for their existing fiber interoffice trunks, as well as for the local loop. Competitive local service providers and competitive access providers (CAPs) with fiber- and radio-distribution networks such as WinStar Communications Inc. (New York) are also in the early stages of WDM implementation.
WDM also provides add/drop muxing for the fiber ring, which lets carriers split waves on a ring among different cities, for instance, using a single mux. Add/drop capability already exists in traditional, copper-based time-division multiplexing (TDM) networks, and carriers currently use WDM to concentrate and consolidate their mix of wide-area network (WAN) platforms. Former standalone Synchronous Optical Network/Synchronous Digital Hierarchy (Sonet/SDH) electronics are now getting integrated into WDM transmission systems, and the groundwork is being laid for direct interfaces of optic/WDM systems into WAN switching and routing hardware. These integrated boxes, such as Lucent Technologies Inc.'s WaveStar, handle WDM, optic routing, Sonet/SDH and network management.
On a Roll
Service providers are buying WDM systems like hotcakes. Barry Flanigan, senior analyst with Ovum Ltd. (London), says several factors are driving WDM deployment today. Among them are the surge in worldwide data traffic, mostly due to Internet bandwidth demands; new competition in global telecom's liberalized markets, which has forced both existing carriers to expand their networks and new operators to grow capacity fast; and optical networking in the telco infrastructure, where WDM can be used for more than just increasing capacity and relieving congestion. "We see price reductions making WDM economically attractive for network applications, and for shorter-distance applications in the metropolitan, interoffice and access regions of the network," says Flanigan.
Ovum expects sales of WDM equipment worldwide to increase from over US$1.1 billion in 1998 to more than $8.6 billion in 2005. North America's market share will fall from around 80 percent to 50 percent during that period, as deployment increases in Europe, Asia and Latin America.
Communications Industry Researchers Inc. (CIR, Charlottesville, Va.) says that WDM has begun to generate significant equipment revenue since 1996, and the hope is that it will drive all-optical switched networks in the future. CIR says leading WDM vendors like Alcatel N.V., Lucent and Nortel Networks Corp. are each shipping a few hundred WDM systems per year.
The average price for WDM systems shipped to service providers in the United States ranges from $500,000 to $2 million, and the pricing is much the same in Europe and the Pacific Rim, according to CIR. Its shipment forecasts, which are somewhat higher than Ovum's, are based on its assumption that telecom traffic growth will drive infrastructure upgrades and that WDM will dominate the high-end Sonet sector by 2007. "The systems at OC-48 and above will increasingly have WDM capability rather than be pure time-division multiplexed Sonet," says Lawrence Gasman, president of CIR.
In contrast, forecasts from Insight Research Corp. (Parsippany, N.J.) are relatively conservative, with WDM and Sonet/SDH markets at nearly US$5.3 billion and $15 billion, respectively, in 2003.
Most WDM vendors today are working on higher-capacity muxes, with 80-wavelength and larger configurations. Although many carriers operate 16- and 40-wavelength implementations, upgrading to the higher-capacity WDM will be simple with the new generation of products.
Vendors are also adding support for Sonet and SDH transport protocols to WDM muxes, which extend Sonet's multiple OC-48 (2.4 Gbit/s) to OC-192 (10 Gbit/s) channel levels and higher, and SDH's synchronous transfer mode (STM) equivalents, from STM-16 to STM-64 and higher.
Hot Stuff
Lucent remains the prime WDM supplier to AT&T, which boasts the highest WDM concentration among all carriers. AT&T's goal is to install some 1,800 WDM muxes by year's end-up from about 1,200 in the first quarter of this year. Most of AT&T's existing WDM systems are 16 wavelengths, but AT&T is also testing Lucent's new WaveStar 400G equipment, which can hit 80 wavelengths.
Lucent is also selling WDM to carriers with large fiber optic and wireless network plans. Among its U.S. customers are Winstar, Global Crossing, Hyperion Communications Inc. (Coudersport, Pa.) and Time Warner Telecom (Greenwood Village, Colo.), while some of the overseas buyers include the Netherlands' KPN Telecom BV, Spain's Telefonica de Espana and Korea Telecom. "We are initially putting in equipment handling 80 wavelengths at OC-48 speeds, but we'll go to 40 wavelengths at OC-192 when that becomes available," says George Simons, senior vice president of network construction and deployment for WinStar.
Simons says capacity expansion will be key for WinStar's intercity and metro ring plans for fiber, which are locally accessed via GHz-level radio, and for its network service for Internet service providers. "Internet traffic is doubling every six to eight months," he says. "Our customers will need a lot of bandwidth, so we are looking for the big WDM systems."
Kathy Szelag, vice president of Lucent's Optical Networking Group, says that while many service deployments today are at lower-wavelength levels, most carriers are starting to test WDM systems handling at 80, versus 16, wavelengths. "The reason is that the initial customer price and other costs for cutting something over at above 16 is better than below 16," she says. "So you might as well just buy the bigger systems and upgrade."
Stan Hanks, vice president of research and technology at Enron Communications (Portland, Ore.), says that once fiber is terminated on the lines, you just bring up a new channel by installing an interface card in the WDM system. "Initially you may need only a handful of channels," says Hanks, "but if traffic needs drive higher, the investment is on hand. A plug-in is simple."
"You can get the equivalents of OC-48 and OC-192 without Sonet but using ATM [asynchronous transfer mode] as the interface," says Mark Allen, manager of technology development at Williams Communications (Tulsa, Okla.), which runs WDM. "The fact is that anybody that doesn't have to do such legacy networking can start right away with 16 or 32 wavelengths or more."
Although carriers worldwide today can deploy 40-wavelength, OC-192 systems, this capacity isn't being fully implemented due to a variety of traffic and economic factors. "It's not just a matter of demand for the hottest stuff," he says. "There is the logistics of all the electronics to be installed. This can be a big capital expense."
Long-distance carrier GST Telecommunications Inc. (Vancouver, Wash.) is sticking with an 8- and 16-wavelength system because its technology is "stable and safe," and its prices are declining with the arrival of the newer WDM technology. "In a year or two, or three, if the fiber is full, you can migrate upward or even swap out systems completely and maybe even skip 32 and 64 wavelengths altogether, and go with 128 or so," says Steve Hemsley, vice president of engineering for GST.
Hemsley says fiber and WDM are the "real" core of the network, versus Internet protocol (IP), ATM and Sonet, which are all basically transient technologies.
In fact, fiber and WDM are becoming nearly synonymous. The two go hand in hand among many of the carrier interconnection agreements, fiber swaps and capacity resale arrangements in the United States. WDM, for instance, was a big part of Williams Telecommunications' capacity-sale deals with WinStar and GST, as well as Enron's with Frontier Communications (Rochester, N.Y.), AT&T's with At Home Corp. (@Home, Redwood City, Calif.), and Global Crossing's with Europe's Unisource consortium. That group consists of DDI Corp. (Tokyo), Level 3 Communications Inc. (Omaha, Neb.) and Cable & Wireless PLC (C&W, London).
On the Fast Track
Meanwhile, carriers want even more capacity and enhanced optics in WDM equipment, and the vendors are taking notice. "By year's end, it will be common to have 200 to 300 Gbit/s per fiber," says Brian McFadden, vice president and general manager of Nortel's OPTera Solutions Division. "The industry is already well beyond 32 wavelengths and into 40-, 50- and 60-wavelength domains. During the fourth quarter we expect more."
More could mean 160-wavelength, 40-Gbit/s systems called OC-768/STM-256, says Ross Nelson, worldwide business development manager for telecom test and measurement at Tektronix Inc. (Wilsonville, Ore.).
Meantime, specifications and standards for WDM's A/D muxes and optical cross-connects-as well as management, test and measurement issues-are among the key topics being addressed by the Optical Internetworking Forum (OIF). The OIF, which includes members from Ciena Corp. (Linthicum, Md.), Cisco Systems Inc. (San Jose, Calif.), AT&T, Telcordia Technologies Inc. (formerly Bellcore, Morristown, N.J.), Hewlett-Packard Co. (H-P, Palo Alto, Calif.), Qwest Communications International Inc. (Denver), Sprint and MCI WorldCom, is also working on direct optical interfaces for routing and switching equipment, as well as interoperability agreements among WDM vendors and service providers.
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