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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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