Dwdm Basics Ciena

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® Fundamentals of DWDM Fundamentals of DWDM

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Fundamentals of DWDMFundamentals of DWDM

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The price of success in the information age can bemeasured in capacity, or sometimes, the lack of it. Asthe information industry evolved, it filled the nation’sfiber optic networks with a voluminous amount ofdata. Corporate intranets led the charge ininformation proliferation, followed by the mass-consumer embrace of the Internet. High-speed PCsfurther fueled the frenzy toward the New World ofconnectivity.

The universal acceptance and adoption ofinformation technology systems quickly aged the verybackbones upon which they were built. Successdepleted the capacity of fiber networks that some 10years earlier were considered practically immortal.

While fiber capacity neared exhaustion, thedemand for extremely high-capacity datatransmissions began to soar. The top rate of 2.4 Gb/sthat many embedded fiber networks generated couldnot satisfy the corporate hunger to deliver greatervolumes of traffic at much higher rates.

Fortunately, the solution to the problem alreadyexisted, at least in its fundamental stage. The trickwould be to meld an architectural approach that

could support today’s bandwidth needs whilegracefully growing with the demands of a network.

Simple solutionsOne answer to the capacity dilemma had beenaround for many years. Wave division multiplexing(WDM) could double capacity by providing twowavelengths that could be transmittedsimultaneously over a single optical fiber. But even

that increase would not solve the problem inthe long term. The optimum solution wouldbe built on the WDM design, but withdensely packed, parallel, discreetwavelengths. The close alignment allowsmore channels to fit on the same fiber.

“There are two major windows in theoptical fiber transmission where the losseshit a minimum. One is 1300 nanometers(nm) and the other is 1550 nm,” explains JoeBerthold, vice president of networkarchitecture for CIENA Corporation. “The firstWDM systems put one channel at 1300 andanother at 1550. That gives you two channelsin one fiber. People started exploiting the1550 band, and some systems put four

channels in that band, which were very widelyspaced. When you begin to pack those channelsmuch more closely together, that is dense WDM(DWDM).”

Eight channels or above is generally consideredthe DWDM operating level. CIENA started theirsystem with 16 channels and then jumped up to a 40-channel system that is scalable to the incredulouslevel of 96 channels. The benefits of thatmagnification become clear in comparison to today’sstandard approach.

For instance, when a 16-channel DWDM system isused to expand a 2.4 Gb/s embedded fiber system, itwill support 40 Gb/s transmissions unidirectionally.

Insatiable Demand for Bandwidth1,200,000






0Apr-96 Jun-96 Aug-96 Oct-96 Dec-96 Feb-97 Apr-97 Jun-97 Aug-97 Oct-97 Dec-97


nel K


ters Shipp


bandwidthThe hungerfor

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And CIENA’s 40-channel system boosts that rate upto 100 Gb/s—equal to the capacity of ten OC-192transmitters.

Not the only game in townOf course, DWDM is not the only way to increase fibercapacity. The most obvious option is to lay morefiber.

“If you have a very short network distance, accessto the rights of way and plenty of time to arrangeconstruction, then burying new fiber is a goodoption,” Berthold explains. “If you’re in an area whereaccess to the rights of way may be difficult, it’s notalways the best choice. For instance, in New York City,even though you may have ductwork where you caninstall the fiber, just getting into the city streets andtying them up is difficult.

“As the distances get longer, it is less of an optionbecause of the high cost in equipping a fiber system.To transmit long distances, you have to do somethingto regenerate or re-amplify thesignals. And that’s costly.”

Another option is to upgrade thetime-division multiplexing (TDM)systems that most carriers alreadyuse. Some TDM upgrades enable 2.5Gb/s or even 10 Gb/s. In fact, TDMgenerally is used in conjunction withDWDM. But the decision to focussolely on an enhanced TDM designgenerally becomes an issue ofeconomics.

“It comes down to dollars and cents.And that decision is based on whattype of fiber you have in the ground,”Berthold explains. “Some fibers makeit extremely difficult to go to 10 Gb/s. They haveimpairments of one type or another that limit how faryou can transmit at 10 Gb/s. It doesn’t mean you can’tdo it. It just means that you have to go to a full-digitaltermination and regeneration much more frequently.”

Thanks to the erbium doped fiber amplifier (EDFA),the reach of a signal boosted by DWDM can extendup to 800 kilometers without the use of electronicregenerators. When you do the math, it’s easy to seethat DWDM will likely come out ahead on a 2.5 Gb/ssystem because it can amplify 40 channels andsupports 100 Gb/s while simultaneously savingmoney on regenerators.

“This is a huge capacity,” Berthold adds. “It’s alsothe most cost-efficient way to achieve that capacity

because you can amplify all the channels in the bandat once and at one cost.”

The emerging optical networkDWDM is possible because of the emergence of newtechnologies. One of the most pivotal is the opticalamplifier, also known as the EDFA. This amplifierboosts all channels equally, simultaneously and in apure optical mode.

EDFAs are fueled by a compound called erbiumthat is incorporated into the fiber using a methodcalled doping. When energy is placed on this fiber,the erbium ions are activated and, in turn, boost theoptical signals that are transmitted over the fiber.

The beauty of this approach is that it reduces theneed for costly signal regeneration units—opticalamplifiers are used instead. Signal regeneratorsrequire a much more circuitous approach to signalstrengthening. They first must convert the opticalsignals to electrical signals, boost them and then

convert them to the optical domain. The approach iscostly and cumbersome.

Although much of the focus is on the transmissionend, DWDM would not be viable without a selectionsystem that precisely separates the channels on thereceiving end. CIENA uses a filtration process calledan in-fiber Bragg grating. Imagine a length of fiberthat has been notched by exposure to an ultravioletelement, creating what is called an interferencepattern. The notches form a pattern on the core of thefiber. Think of the pattern of notches as a mirror. Thespace between each of the mirrors determines whichchannel is reflected and is clearly separated from allof the others.

Such a fiber-grating system fulfills the promise of

DWDM—The Third Dimension

TDM • OC48 = 2.5 G/bs• OC192 = 10 G/bs

• OC48 x 16 ch. = 40 G/bs• OC48 x 24 ch. = 60 G/bs• OC48 x 40 ch. = 100 G/bs


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DWDM by receiving what has been transmitted.Other issues of performance revolve around laser

technologies and the placement of amplifiersthroughout the network. Optical amplifiers produceamplified spontaneous emissions that can decreasethe signal-to-noise ratio (SNR) and ultimatelydegrade the signal.

The goal with DWDM is to deliver a continuousamount of transmit power that keeps the laser stableand the SNR at an optimum level.

“You need lasers that can be as stable as thefilters,” Berthold says. “If the laser is extremely stableand the filter is extremely precise, then you can putchannels very close together.”

One advancement that will lead DWDM into futureapplications is the way in which it uses multiplexers.Today’s DWDM architectures form the foundation ofwhat will eventually become an optical network. Keybuilding blocks in that network are optical add/dropmultiplexers (OADMs). These versatile elementsempower carriers to customize traffic flow formaximum efficiency and performance. Whileelectronic add/drop multiplexers mustterminate the entire optical signal,optical add/drop multiplexers savecarriers money by only terminating aselected subset of the optical channelson the fiber. OADMs can be substitutedfor optical amplifiers and give anetwork flexibility by allowing traffic tobe dropped or added in up to four OC-48 channels between DWDM terminals.

OADM is the stepping stone to theoptical network because it can act as alink that can be modified for differentnetwork configurations.

Real world viewBeyond the gleaming nuts and bolts of a DWDMsystem lies the stellar attraction: the real-worldapplication. One of the most dramatic applications isSprint’s recently announced selection of CIENA’s 40-channel MultiWave Sentry™ 4000 that will initiallyexpand its network capacity by 250 percent andultimately up to 600 percent.

Sprint is the first interexchange carrier to launch a40-channel DWDM system. One of the biggestfeatures of the MultiWave Sentry 4000 is that it isscalable from 40 to 96 channels.

The system interconnects with Sprint’s OC-48SONET equipment and can support more than threemillion phone calls over a single fiber pair.

“One of the great things about DWDM is that it’sincremental,” says Berthold. “Today, you could put ona 40-channel system and equip it with just onechannel. Then you could add a second or third andjust keep populating it as the demand requires.

“If you had the traditional SONET/TDMconfiguration and wanted to deploy a system thathad 10 Gb/s total capacity, on Day 1 you have to putin the most expensive parts, the parts that deal withthe line system at 10 Gb/s. Then, as you need to putadditional capacity on the system, you add therelatively inexpensive parts, which are the line cards.

“The DWDM system is equipped with amplifiersthat set up the link needed for one channel. But thenmost of the additional cost is in the channel cards.You only pay for them when the capacity is needed.So, you get a system capable of 96 channels, but itmight only be equipped with eight channels, andthat’s all you’d pay for.”

Keeping the options openThe great majority of DWDM deployment has been in

North America, although other parts ofthe world are beginning to embrace theapproach as well. CIENA products followan open-standard interface using the ITUmanagement standard called Telecom-munications Management Network(TMN).

For now, carriers are preparing for adomestic landslide in the demand forbandwidth-hungry products, includingmultimedia and high-speed accessproducts.

“Much of the fiber that’s deployed inthe country today is not going to support40 Gb/s economically,” Berthold

explains. “This is where the DWDM technology isoffering a whole new advantage of carrying thesehigh-rate channels and making the networks muchless expensive.

“The wide-scale deployment of DWDM ishappening at a very fast pace. The largest carriers areall doing national-scale network build-outs withDWDM. All the major routes in their networks have atleast one DWDM system.”

The rate at which the technology is beingembraced is very telling about its perceived futurepotential. Such enthusiasm for DWDM begs thequestion about coming innovations. If this is thebasis for optical networks, how far and how fast mustwe go to get there?

MultiWave Sentry™ 4000

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The future looks rosy for the bandwidth enhancer ofthe fiber optics network, also known as densewavelength division multiplexing (DWDM). Withcarriers looking for faster ways to transmit more dataat cheaper costs, no other technology can live up tothe challenge quite like DWDM.

“In 1995, the total capacity of a single fiber was 2.5Gb/s. In 1998, the capacity has gone to 96 times thatof 2.5 Gb/s,” says MatSteinberg, director ofoptical networking for ryanhankin kent.

“You’re also seeingcarriers redesign theirentire switched networks.They are looking at packet-based or cell-basedswitching instead of circuit-switching. That’s gettingaway from the traditionaltelephone network,”Steinberg says. “Companieslike Sprint are looking to dothat in about three-to-five years. All the other carriersare trying to do something similar, as well. You’ve gotincredible capacity coming on-line, and you’ve gotcarriers that want to use their embedded plant moreefficiently.”

That transformation is pushing equipmentspending through the roof. Worldwide consumptionof open-link DWDM systems came in at $626 millionin 1996. By 2001, that number is expected toskyrocket to $4.64 billion, an average annual growthrate of 49%. While 90% of the 1996 spending camefrom North American consumption, watch for DWDMto take on a more international presence, especiallyin Europe and the Pacific Rim.

“Japan is expected to have the fastest DWDMgrowth rate, from 1%—or $9 million—in 1996, to143% per year in 2001,” says Stephen Montgomery,president of ElectroniCast Corporation. “By the year2001, we expect them to spend $790 million on

DWDM equipment, which would represent 17% of themarket.

“The growth won’t just be in Japan,” Montgomeryadds. “In the last few years, China has deployed fibercable between each major province and each majorcity. But the problem is that their fiber count is stillvery low. We’re not talking about hundreds ofinstalled fibers. We’re talking less than 10 installed

fibers, maybe two or four fibers per cable, which ismore than adequate right now. But, in 10 years, wesee them having a demand for more.”

Complementary styleThe enormous capacity that only DWDM can providemay be the hottest thing going. But how well do theywork with existing telecom equipment?

“It makes a beautiful fit,” says Joe Berthold, vicepresident of network architecture for CIENACorporation. “One of the reasons these systems areso successful is that they are so simple. They do notrequire any fundamental change in networkarchitectures. It appears as if the fiber just magicallygot magnified. We call it virtual fiber.”

CIENA embarked on the DWDM market with itsMultiWave®1600. The product dramatically enhancedperformance by applying 16 wavelengths of OC-48 toa single fiber. By placing a 16-channel DWDM unit on

Thething going

CIENA DWDM Creates “Virtual Fiber”

Yields Virtual FiberTM, Fast Capacity Growth

low fiber count cable

Virtual FiberTM• increases capacity• defers new construction• allows modular growth


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a 2.5 Gb/s fiber, the transmission rate swells to 40Gb/s. Consequently, the number of voice or data callsthat a fiber strand can handle jumps from 32,000 to512,000. The feat is even more remarkableconsidering that the performance is magnified up tosixfold with CIENA’s MultiWave Sentry 4000, whichdelivers 40 channels and scales up to 96.

From an operations standpoint, the appeal is theease of installation.

“You simply connect the unit to the existingSONET equipment,” Berthold explains. “The SONETequipment does everything it did before. The onlyaddition is that now you have new networkmanagement elements.”

Managing the high-speed networkHigh at the top of many carriers’ wish lists is an easily managed performance-monitoring system. Toomany current designs require ancillary softwareadditions that complicate monitoring and raise theprice.

“When CIENA introduced their system a couple ofyears back, they had the foresight to accommodatethe software requirements of the carriers,”Montgomery explains. “Other manufacturers fellshort and put the weight of software management ontheir customers. So the carriers were actually in theprocess of either putting together their own softwareor hiring an outside firm to do it.

“CIENA and some other vendors saw this asimportant from the very beginning. Because of that,they have a leg up on the industry, and that’s one ofthe major reasons why they are successful.”

Network management programs are a point ofdistinction for DWDM systems. CIENA made its markwith its flagship management system called

WaveWatcher®. This watchdog is unique in its abilityto monitor analog and digital performance.

Although it is vital to continuously assess thehealth of signals that pass through a system, carriers also must rely on vendors that can cost-efficiently bundle a program like WaveWatcher with aDWDM unit like MultiWave Sentry 4000. Without such turnkey solutions, carriers would be left out in the cold in this highly technical, dynamic industry.

“Carriers are emphasizing the need for continualmonitoring of all performance elements throughoutthe network,” according to an ElectroniCast report onDWDM. “This requires software of continuallyincreasing complexity. A general rule of thumb is that

the software represents 40% to 50% of the cost, and the optoelectronics and fiber represent 30% to 40%. The electronic mux/demux, monitoring/instrumentation and various otherintegrated circuits represent 20% to30%.

“Most carriers do not have internalstaff capability to develop, maintainand upgrade the required software.Any network expansion, by WDM orotherwise, must include the necessarynetwork management softwareupgrade, and this, in general, must be

provided by the vendor.” Another crucial element in network management is

an open architecture. WaveWatcher supports thebreadth of management systems used domesticallyand abroad. The list includes simple networkmanagement protocol (SNMP), which is often usedby companies with a propensity toward on-linesystems; ITU’s Telecommunications ManagementNetwork (TMN); and transaction language 1 (TL1),which is popular among the Bell regional holdingcompanies.

“WaveWatcher supports a variety of standardsseamlessly,” Berthold says. “It also can be done inparallel so that someone could look at the networkthrough SNMP. Someone else might use a TL1 link to a legacy system, and a new managementapplication could be using the TMN interface at thesame time.”

WaveWatcher functions in tandem with thenetwork by running on a parallel optical servicechannel. Its constant surveillance takes a microscopicapproach to system control.

“These systems are extremely intelligent,” Berthold

First Generation DWDM

Yields Virtual FiberTM-Fast Capacity Growth

low fiber count cable

Virtual FiberTM• increases capacity• defers new

construction• allows modular


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explains. “Every single circuit board hasmicroprocessors on it. They do self-inventory. Theycan report to the management system about the localstatus, what’s equipped and what software is turnedon and active.

“We manage a whole end-to-end system. Forinstance, the transmission system might have aterminal at one end and go through seven amplifiersto a terminal at the other end. WaveWatcher providesvisibility from both ends through all the pieces ofequipment by having a separate channel that goesalong the fiber and carries the information.

“Each of our amplifiers also is very heavilyinstrumented with sensors that are watching all thethings that are critical to the operation,” Bertholdadds. “You have a processor that digests that androutes the information back to the terminals.”

Because the system can be operated remotely,carriers can maintain greater control. That flexibilityis paramount.

“WDM systems werereally used for point-to-point relief,” rhk’s Steinbergsays. “Yet carriers want tomanage their network froma couple of locations. If youput DWDM on a routebetween San Francisco andSalt Lake City, you mightwant to manage that from acentral location. That’s oneof the things carriers arelooking for. They wantenhanced monitoringcapability because theyhave so much traffic on asingle fiber, let alone on thecable.”

For optimum network performance, carriers useCIENA’s WaveLock system to keep channels on theirassigned frequencies.

“This is a closed-loop feedback system that allowsus to maintain very high stability,” explains TomMock, CIENA’s product marketing director for accessproducts. “WaveLock involves some very selectivefilters on the receive end that allow us to discriminatebetween adjacent channels very effectively. This isimportant because it lets us space our channelscloser together so we can get more channels in theavailable bandwidth.

“Our current 40-channel product is using 50 GHzchannel spacing, which is the tightest in the industry

by at least a factor of two. WaveLock is key to ourbeing able to achieve that spacing.”

Power to the Nth degreeWhat’s the use of technology without the power tomake it function? Power can be a necessary evil,particularly if it is not managed correctly. Thecomplexity of sophisticated optical systems canmake span management a daunting task.

The challenge in powering a DWDM system is toprovide a constant supply to each channelsimultaneously. Without it, the system will notperform in a predictable, optimal fashion.

“We automatically adjust the amplifiers so that thepower on each individual channel remains constant,regardless of how many channels are added ordropped at any given time,” explains Mock. “Carrierscan add channels to the network or take them awayand not worry about having to go back to adjustamplifiers that are between terminals.

“Span management also ensures that the systemdoes not have duplications installed that mightinterrupt service. In addition, it keeps track of theconfiguration of the network, such as what channelsare installed at each location.”

With DWDM, the rate at which people cancommunicate and distribute information will grow inquantum leaps. It will change not only how wecommunicate, but also what we communicate.Multimedia libraries and bandwidth-hungry graphicswill effortlessly zip across a DWDM-empoweredsystem. The breadth of change from a one-channelfiber to 96 in little more than 10 years leaves youwondering if the sky is truly the limit.

The MultiWave® System

WaveWatcher®Element Management System




nel u



channel units


MultiWaveOptical Line Amplifier

MultiWaveOptical Line Amplifier

MultiWaveOptical AddDrop Mux

λ1 λn λ1 λn

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The breakneck pace at which fiber capacity ismultiplying makes it difficult to fathom that we haveonly scratched the surface of what this remarkablemedium can potentially yield. Fiber’s increasingly

broad base is the foundation for the gee-whizapplications that will transform the Internet as weknow it, making today’s approach archaic bycomparison.

Dense wavelength division multiplexing (DWDM)is the latest technology darling to expand fiber’spotential. It lays the groundwork for true opticalnetworking and gives carriers a path to reach theirgigabit desires.

“DWDM is the basis for optical networking like timedivision multiplexing was the basis for electricalnetworking,” says Mat Steinberg, director of opticalnetworking for ryan hankin kent. “To do TDM, peopleused electrical multiplexers and electrical cross-connects.

“Now people are starting to look at channels ofwavelengths that today could be as much as 10 Gb.

And what was done with electrical networking is whatpeople are looking at for optical networking. Now youhave to implement optical networking systems andfind the right mix of electrical and optical

intervention. These arethe issues that areopen for debate in theindustry.”

Many pieces of thepuzzle must fall intoplace as the industryhashes out the bestapproach to the opticalnetwork. The ever-present issue of openvs. closed interfacesrears its head in the debate, as dobroadband switching

approaches. It may not be a short road to reach thishigher operating plan, but it undoubtedly will be aninteresting one, full of innovation along the way.

On the verge of greatnessThe fiber phenomenon is a one-way ride straight up.Worldwide purchase of fiber -optic-relatedequipment is mushrooming from $4.52 billion in1996 to an estimated $34.2 billion by the end of 2006,according to ElectroniCast Corporation. The lion’sshare of that consumption is for fiber transportterminals, including DWDM SONET/SDH terminals.

Some of that investment is from new fiberbuildouts by carriers that have the foresight to useDWDM to extend the life of their systems.

This is especially important with undersea routeswhere it is cost-prohibitive to access and lay



Open vs. Closed Optical Interfaces

Open Closed

Optical layerN X OC-48/192


N X OC-48/192


Voice OtherCircuit Router ATMVoice Other

CircuitRouter ATM

Standard Open InterfacesDirect connection supported

Closed/Proprietary specification for Optical Layer Interfaces


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additional fiber for capacity upgrades.Domestically, competition is the impetus that

draws carriers to the DWDM solution. The increasingreliance on data, particularly by corporate America,has pushed embedded fiber systems close to theirlimits. As intranets take on even greater strategicimportance, corporations are looking for the fastest,most cost-effective route to retain connectivity. Andthese sophisticated consumers will follow the carrierthat can deliver it. Therefore, to stay in the game,carriers must prepare their networks for this data-centric view of the world where capacity is king.

The influence of burgeoning capacity already isbeing felt. For example, Bell Atlantic forecasts a 35%growth in T-1 lines this year. The company’s DS-3 45Mbyte services are expected to jump 39%. However,these are eclipsed by projections for frame relay,which is expected to grow by 55 percent annually.

Onward to gigabitsThe market potential for these data-centric networksdraws carriers to gigabit solutions like bees to honey.This has exponentially boosted the expansion of fibercapacity to the highest capacity available in CIENACorporation’s MultiWave Sentry™ 4000. Thistrendsetter uses DWDM to scale from 40 channels ona single fiber up to 96 channels. That’s a far cry from

the single strands that were state-of-the-art in themid-1980s.

“We’re basically on the verge of increasing thecapacity 100-fold,” says Steinberg. “Within a year,you’ll see a terabyte down a fiber—that’s 1012 b/s.”

The MultiWave Sentry 4000 is part of CIENA’sMultiWave line, the company’s family of opticalnetworking products. Along with the high capacity,MultiWave incorporates expanded networkmanagement features and a technology calledDirectConnect that is a direct link to the opticalnetwork.

This easy interface provides some functions ofSONET, including performance monitoring, thatallows problems to be sectionalized by location.

Network Architecture


SONET SDHAsync PDH Standard Short-reach Interfaces

DWDMPhysical Fiber

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“DirectConnect allows you to take higher-speedinterfaces from devices such as asynchronoustransfer mode switches or routers and apply thatdirectly to the optical transport layer,” explains TomMock, CIENA’s product marketing director for accessproducts. “You don’t have to go through a TDMmultiplexer, like a SONET multiplexer.

“It also allows you to directly interconnect WDMsegments, so you don’t need any kind of externalregeneration. You can interconnect the long-haul andshort-haul portions of the network to build aconnection from an ATM switch. It would connectthrough the access network over the interofficenetwork and then over the long-haul network withoutever having to go to any other kind of equipment.”

ATM appealCarriers are racing to keep up with the growingpopularity and data requirements of ATM. A few yearsago, the highest speed of an interface card on eitheran ATM switch or Internet protocol (IP) router was155 Mb/s. In 1997, that escalated to 622 Mb/s. Nowthe bar has beenraised to 2.5 Gb/s.

Such high ratescan complicatenetwork config-uration, or in thecase of DWDM,complement it.

“DWDM is really anatural fit to thatkind of equipment,”says Joe Berthold,vice president ofnetwork architecturefor CIENA. “Youcould take theoutput of an ATM switch and plug it straight into apiece of DWDM equipment, transport it across thecountry and hand it back to another ATM switch.

“Without a DWDM transport system, a carrierwould have a hard time transmitting at 2.5 Gb/s. Youcouldn’t do SONET multiplexing because your signalwas already up at the fiber optic line rate that thecarrier was able to support at 2.5 Gb/s. DWDM allowsyou to operate at the high rate, and because ours isan open system, you can separate it from the ATMswitches and the IP routers.

“You don’t have to become an expert on theesoteric technology of DWDM and the nonlinearitiesof long-distance fiber optics and optical amplifiers.

You just have to plug in a piece of DWDM equipmentand send your signal across the country,” Bertholdadds.

An open or closed caseAs the number of carriers rises and the convergenceinto each other’s markets continues, standardsbecome increasingly important. Network designerswould be wise to learn from the painful lessons ofwireless carriers that failed to follow a singlestandard when launching their early networks.

From the beginning, CIENA has embraced anopen-system philosophy by complying with industrystandards.

DWDM came into the market with two approaches:a SONET-centric approach and a view of thetechnology as a completely new transport layer. Toincrease capacity in the SONET view, vendors wouldtake the necessary components and technology of aDWDM system and integrate it into their SONETterminals.

“For instance, they would take a loosely specifiedlaser card on aSONET terminal andreplace it with a veryspecific wavelength,”Berthold explains.“They would usepassive componentsto combine thesesignals out of the SONET equip-ment and send itacross the fiber. Theywould then haveamplifiers and a wayto manage thoseamplifiers. Finally,

they would send the signals through filters toseparate them out and then send them on to theSONET receivers.”

One of the prime problems with this approach isthat it is a closed system. The carrier is locked intothe vendor’s approach and their proprietarytechnology.

“We’ve taken the approach that DWDM is a wholenew transport layer,” Berthold adds. “It’s thebeginning of optical networking. It’s a layer that’sgoing to be very simple and allow you to streamlinenetworks. We have a standard OC-48 interface that isopen. It’s a SONET short-reach interface that allowscarriers to use very inexpensive optics.

The “Last Mile” Challenge


Central Office


AccessHigh speed data,ATM


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“Anyone who has a standard SONET signal canplug it into Vendor A’s equipment or Vendor B’sequipment. You’re not tied to any particular SONETvendor.”

The promise of opticalnetworkingIf DWDM is the first step to optical networking, thesecond step is a standardapproach. For opticalnetworking to realize its fullpotential, there must be astandard interface to the opticaltransport layer. An openarchitecture allows multiplevendors to connect to a networkwith different kinds ofequipment. It also stimulatesthe innovation of products thatfurther advance the technology.

Such products will takecarriers from optical transport tooptical networking. They mustalso be dynamic with the abilityto adapt as the marketdemands. CIENA’s MultiWavesolutions fit this bill and set thestage for the next level ofinnovation.

“Eventually, a customer will be able to ask for anoptical channel from their office in New York to theiroffice in Dallas,” Berthold predicts. “A carrier will beable to sit down at a terminal and set it upautomatically.”

Before the industry can move forward to thisadvanced stage, solutions must be designed to buildswitching right into the optical layer.

“The biggest issue in terms of implementingoptical switching in networks is providing a solutionthat’s cost-effective,” Mock says. “As you look at whatwe can provide today with our Direct Connectinterfaces, we can do manual bandwidthmanagement with simple patch cords. The next stepwill be dynamic bandwidth management.”

Think globally, act locallyThe early DWDM designs were built to fulfill theneeds of the long-distance carrier. While that demandstill exists, the need for DWDM on the local front isgrowing.

“The market is waiting for metropolitan, ring-basedsystems,” Steinberg says. “Some education still

needs to be done on how to manage and use it. But Ibelieve that it will revolutionize how local networksare built.”

Carriers have strong incentive to bring DWDM tometropolitan areas. Expect the momentum forWAN/LAN applications to accelerate over the nextfew years. Four years from now, that market will enjoyabout a 40% annual growth rate, according to

Steinberg.CIENA is prepared to

address the local market withtwo products. The MultiWave®

Firefly is designed for point-to-point short-haul applicationsin the public network.MultiWave Metro™ is beingdeveloped for ring-based metroapplications.

“Our access and interofficeproducts do not require opticalamplifiers. So, removing themmakes these network elementsless costly and simpler,” Mockexplains. “We’ve also madesome changes in how multiplexing and demulti-plexing is done, and in themodulation/demodulation.This optimizes the product for

use over shorter distances of fiber.”

There’s no stopping progressWho would have thought that a single strand of fiberoptic glass could so change the ways wecommunicate. Not only did it re-energizetelecommunications with a wealth of newtechnologies, but it helped vitalize the worldeconomy. More importantly, it changed the way people thinkabout communicating. Thanks to the on-lineconnection, an infinite amount of material is readilyavailable. Multimedia, sophisticated audio andgraphics all blend for instantaneous communicationsaround the world.

This is possible in great measure because of theavailability of fiber optics. More incredulous is thefact that this flexible and voluminous medium is onlyin its infancy.

If the capacity grows at the 100-fold rate that it hasover the last few years, imagine where the road willultimately lead. Count on it to be a very exhilaratingride.

Moving to a Data-Centric Network


ATM Switch

IP Router



Transport Facilities(DWDM)622 Mb/s 45 Mb/s

155 Mb/s

2.5 Gb/s

ATM Switch

IP Router


Transport Facilities(DWDM)

2.5 Gb/s

2.5 Gb/s