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Extensions to fiber optics will supply network capacity that borders on the infinite

Gary Stix, Staff Writer


FIBER LEADS in performance improvements. The number of bits a second (a measure of fiber performance) doubles every nine months for every dollar spent on the technology. In contrast, the doubling time for the number of transistors on a computer chip occurs every 18 months—a trend known as Moore’s law. Over a five-year period, optical technology far outpaces silicon chips and data storage. Graph By: CLEO VILETT, SOURCE: Vined Khoslan, Kleiner, Caufield and Perkins.
Was it Britney Spears or Fatboy Slim? The network administrators at Kent State University had not a clue. All they did know last February was that "Rockefeller Skank" and hundreds of other downloading hits had gotten intermingled with e-mails from the provost and research data on genetic engineering of E. coli bacteria. The university network slowed to a crawl, triggering a decision to block access to Napster, the music file-sharing utility.

As demand for network capacity soars, the Napster craze may mark only the opening of the first of many floodgates. Venture capitalists, in fact, have wagered billions of dollars on technologies that may help telecommunications companies counter the prospect that a video Napster capable of downloading anything from Birth of a Nation to Rocky IV might bring down the entire Internet.

PowerPoint slides at industry conferences emphasize why the deluge is yet to come. Video Napster is just one hypothesis. A trillion bits a second--the average traffic on the Internet's backbones, its heaviest links--may fulfill less than a thousandth of future requirements. Online virtual reality could overwhelm the backbones with up to 10 petabits a second, 10,000 times more than today's traffic. (A petabit is a quadrillion bits, a one with 15 trailing zeros.) Computers that share one another's computing power across the network--what is called metacomputing--might require 200 petabits.

If these scenarios materialize--and, to be sure, people have been tapping their feet for virtual reality for more than a decade--the only transmission medium that could come close to meeting the seemingly infinite demand is optical fiber, the light pipes trumpeted in commercial interludes about the "pin drop" clarity of a connection. Fiber links can channel hundreds of thousands of times the bandwidth of microwave transmitters or satellites, the nearest competitors for long-distance communications. As one wag pointed out, the only other technology that comes close to matching this delivery capacity is a panel truck full of videos.

The race to augment the fiber content of the world's networks has started. Every day installers lay enough new cable to circle the earth three times. If improvements in fiber optics continue, the carrying capacity of a single fiber may reach hundreds of trillions of bits a second just a decade or so from now--and some technoidal utopians foresee the eventual arrival of the vaunted petabit mark. To break that barrier, however, will require both fundamental breakthroughs and the deployment of technologies that are still more physics experiments than they are equipment ready to be slotted into the racks on nationwide phone and data networks.

New photonic technologies, which use lightwaves instead of electrons for signal processing, will make current electronic switching systems obsolete. Even now the transmission speeds of the most advanced networks--at 10 billion bits a second--threaten to choke the processing units and memory of microchips in existing switches. As the network becomes faster than the processor, the cost of using electronics with optical transmissions skyrockets. The gigabit torrent contained in a wavelength of light in the fiber must be broken up into slower-flowing data streams that can be converted to electrons for processing--and then reaggregated into a fast-flowing river of bits. The equipment for going from photon to electron and back to photon not only slows traffic on the superhighway but makes equipment costs soar.

While network designers contemplate the prospect of machine overload, hundreds of companies, big and small, now grapple with creating networks that can exploit fiber's full bandwidth by transmitting, combining, amplifying and switching wavelengths without ever converting the signal to electrons. Photonics is at a stage that electronics experienced 30 years ago--with the development and integration of component parts into larger systems and subsystems. A rising tide of venture capital has emerged to support these endeavors. In the nine months of 2000, venture funding for optical networking totaled $3.4 billion, compared with $1.5 billion for all of 1999, although this may have eased in recent months. The success of a stock like component supplier JDS Uniphase stems in part from the perception that its edge in integrated photonics could make it the next Intel.

Investment in optical communications already yields payoffs, if fiber optics is matched against conventional electronics. The cost of transmitting a bit of information optically halves every nine months, as against 18 months to achieve the same cost reduction for an integrated circuit (the latter metric is famous as Moore's law). "Because of dramatic advances in the capacity and ubiquity of fiber-optic systems and subsystems, bandwidth will become too cheap to meter," predicts A. Arun Netravali, president of Lucent Technologies's Bell Laboratories in a recent issue of Bell Labs Technical Journal.

Identical forecasts about a free resource eventually came to haunt the nuclear power industry. And the future of broadband networking, in which a full-length feature film would be transmitted as readily as an e-mail message, is still not a sure bet. A decade ago telecommunications providers and media companies started preparing for the digital convergence of entertainment and networking. Five hundred channels. Video on demand. We're still waiting. Meanwhile the Internet, once viewed as a quaint techno sideshow for the government and schoolkids, has transmuted into the network that ate the world. E-mails and Web sites have triumphed over Mel Gibson and Cary Grant.

And Then There Was Light

Technologies for all Optical Networks
Prospects of limitless bandwidth--the basis for speculations about networked virtual reality and high-definition videos--are of relatively recent vintage. AT&T and GTE deployed the first optical fibers in the commercial communications network in 1977, during the heyday of the minicomputer and the infancy of the personal computer. A fiber consists of a glass core and a surrounding layer called the cladding. The core and cladding have carefully chosen indices of refraction (a measure of the material's ability to bend light by certain amounts) to ensure that the photons propagating in the core are always reflected at the interface of the cladding. The only way the light can enter and escape is through the ends of the fiber. To understand the physics behind how a fiber works, imagine looking into a still pool of water. If you look straight down, you see the bottom. At viewing angles close to the water, all that is perceived is reflected light. A transmitter--either a light-emitting diode or a laser--sends electronic data that have been converted to photons over the fiber at a wavelength of between 1,200 and 1,500 nanometers.

Today some fibers are pure enough that a light signal can travel for about 80 kilometers without the need for amplification. But at some point the signal still needs to be boosted. The next significant step on the road to the all-optical network came in the early 1990s, a time when the technology made astounding advances. It was then that electronics for amplifying signals were replaced by stretches of fiber infused with ions of the rare-earth element erbium. When these erbium-doped fibers were zapped by a pump laser, the excited ions could revive a fading signal. The amplifiers became much more than plumbing fixtures for light pipes. They restore a signal without any optical-to-electronic conversion and can do so for very high speed signals sending tens of gigabits a second. Perhaps most important, however, they can boost the power of many wavelengths simultaneously.

TODAY’S ADVANCED NETWORKS maintain mostly separate electronic connections for voice and data and achieve reliability using rings based on the Synchronous Optical Network (SONET) communications standard: if one link is cut, traffic flows down the other half of the ring. The SONET multiplexer aggregates traffic onto the ring.
TOMORROW’S NETWORKS will channel all traffic over the same fiber connection and will provide redundancy using the Internet’s mesh of interlocking pathways: when a line breaks, traffic can flow down several alternating pathways. Optical switching will become the foundation for building these integrated networks.
This ability to channel multiple wavelengths enabled the development of a technology that has helped drive the frenzy of activity for optical-networking companies in the financial markets. Once you can boost the strength of multiple wavelengths, the next thing you want to do is jam as many wavelengths as possible down a fiber, with a wavelength carrying as much data as possible. The technology that does this has a name--dense wavelength division multiplexing (DWDM)--that is a paragon of technospeak.

DWDM set off a bandwidth explosion. With the multiplexing technology, the capacity of the fiber expands by the number of wavelengths, each of which can carry more data than could be handled previously by a single fiber. Nowadays it is possible to send 160 frequencies simultaneously, supplying a total bandwidth of 400 gigabits a second over a single fiber. Every major telecommunications carrier has deployedDWDM, expanding the capacity of the fiber that is in the ground, spending what could be less than half of what it would cost to lay new cable, while the equipment gets installed in a fraction of the time it takes to dig a hole.

In the laboratory, meanwhile, experiments point toward using most of the capacity of fiber--dozens of individual wavelengths, each modulated at 40 gigabits or more a second, for effective transmission rate of a few terabits a second. (One company, Enkido, has already deployed commercial link containing a 40-gigabit-a-second wavelengths.) The engorgement of fiber capacity will not stop anytime soon and could reach as high as 300 or 400 terabits a second--and, with new technical advances, perhaps exceed the petabit barrier.

The telecommunications network, however, does not consist of links that tie together point A and point B--switches are needed to route the digital flow to its ultimate destination. The enormous bit conduits that now populate laboratory testbeds will flounder if the light streams are routed using conventional electronic switches. Doing so would require a multiterabit signal to be converted into dozens or hundreds of lower-speed electronic signals. Finally, switched signals would have to be reconverted to photons and reaggregated into light channels that are then sent out through a designated output fiber.

The cost and complexity of electronic switching have prompted a mad scramble to find a means of redirecting either individual wavelengths or the entire light signal in a fiber from one pathway to another without the optoelectronic conversion. Research teams, often inhabiting tiny startups, fiddle with microscopic mirrors, liquid crystals and fast lasers to try to devise all-optical switches.

All-optical switching, however, will differ in fundamental ways from existing networks that switch individual chunks of data bits, such as IP (Internet Protocol) packets. It is an easy task for the electronics in routers or large-scale telephone switches to read on a packet the address that denotes its destination. Photonic processors, which are at about the same stage of development that electronics was in the 1960s, have demonstrated the ability to read a packet only in laboratory experiments.

Optical switches heading to the marketplace hark back to earlier generations of electronic equipment. They will switch a circuit--a wavelength or an entire fiber--from one pathway to another, leaving the data-carrying packets in a signal untouched. An electronic signal will set the switch in the right position so that it directs an incoming fiber--or a wavelength within that fiber--to a given output fiber. But none of the wavelengths will be converted to electrons for processing.

Optical-circuit switching may be only be an interim step, however. As networks get faster, communications companies may demand what could become the crowning touch for all-optical networking, the switching of individual packets using optical processors

With the advent of optical packet switching, individual packets will still need to get read and routed at the edges of optical networks--on local phone networks near the points where they are sent or received. For the moment, that task will still fall to electronic routers from companies such as Cisco Systems. Even so, the evolution of optical networking will promote changes in the way networks are designed. Optical switching may eventually make obsolete existing lightwave technologies based on the ubiquitous SONET (Synchronous Optical Network) communications standard, which relies on electronics for conversion and processing of individual packets. And this may proceed in tandem with the gradual withering away of Asynchronous Transfer Mode (ATM), another phone company standard for packaging information.

In this new world, any type of traffic, whether voice, video or data, may travel as IP packets. A development heralded in telecommunications for at least 20 years--the full integration of voice, video and data services--will be complete. "It's going to be a data network, and everything else, whether it's voice or video, will be applications traveling over that data network," says Robert W. Lucky, a longtime observer of the telecommunications scene and director of research for the technology development firm Telcordia.

When you ring home on Mother's Day, the call may get transmitted as IP packets that move on a Gigabit Ethernet, a made-for-the-superhighway version of the ubiquitous local-area network (LAN). Gigabit Ethernet would in turn ride on wavelength-multiplexed fiber. Critics of this approach question whether such a network would provide ATM and SONET's quality of service and their ability to reroute connections automatically when a fiber link is cut.

Life would be simpler, though. The phone network would become just one big LAN. You could simply slot an Ethernet card into a computer, telephone or television, a far cheaper and less time-consuming solution than installing new SONET hardware connections. Some companies are even now preparing for the day when IP reigns. Level 3 Communications, a carrier based in Denver, has laid an international fiber network stretching more than 20,000 miles in both the U.S. and overseas. Although the network still relies on SONET, CEO James Q. Crowe foresees a day when these costly legacies of the voice network will wither into nothingness. "It will be IP over Ethernet over optics," Crowe says.

Home Light Pipes

Even if network engineers can pare down the stack of protocols that weighs heavy on today's network, they must still contend with the need to address the "last mile" problem, getting fiber from the curbside utility box into the TV room and home office. Some builders now lay out new housing projects with fiber, presaging the day when households routinely get their own wavelength connection. But cost still hangs over any discussion of fiber to the home. Until recently, advanced optical-networking equipment, such as DWDM, was too expensive to consider for deployment on regional phone networks. Extending the equipment into a wall panel of a split level--at perhaps $1,500 a line--still costs more than all but a few are willing to pay. Most people have yet to take delivery of their first megabit connection. So it remains unclear when the time will come when the average household will need the gigabits to project themselves holographically into a neighbor's house rather than just picking up the phone.

Dousing "Help me, Obi-Wan Kenobi" fantasies, engineers are confronting an array of nettlesome technical problems before a seamless all-optical network can become commonplace. Take one example: even with lightwave switching in place, one critical part of the network requires conversion to electronics. About every 120 miles, a wavelength has to be converted back to an electronic signal to restore the shape and timing of individual pulses within the vast train of bits that occupy each lightwave.

DEMAND GAP for use of optical-fiber backbone—the most heavily used links—emerges in a study by market researcher Adventis that shows that supply will overmatch demand. Yet new applications such as virtual reality or metacomputing could require huge increments in optical bandwidth from the few terabits per second currently required to meet needs on U.S. telecommunications back bones.
Equipment suppliers also struggle mightily with electronics envy. Component suppliers such as JDS Uniphase labor on methods to build modules that combine lasers, fiber, filters and gratings (which separate wavelengths). Building photonic integrated circuits remains difficult. Photons can't store charge, as the negatively charged particles called electrons do. So there is no such thing as a photonic capacitor that will store zeros and ones indefinitely. Moreover, it is difficult to build photonic circuitry as small as electronic integrated circuits, because the wavelength of infrared light used in fiber-optic lasers is about 1.5 microns, which places limits on how small you can make a component. Electronic circuits reached that dimension more than a decade ago.

The good news is that companies both small and big are now trying to solve problems such as signal restoration, and a pot of venture money exists to fund them. The field, which has taken on the same aura that genomics now holds and dot-coms once did, has become an exemplar of a new, hyperventilating model of research. Tiny development houses proceed until they can furnish some proof that they can make good on their promises, and then they are bought out by a Nortel, Cisco or Lucent.

"It's a crazy world," says Alastair M. Glass, director of photonics at Lucent. "Anyone can go out with the dumbest ideas and get funding for them, and maybe they'll be bought for big bucks. And they've never made a product. I mean this is new. This has never happened in the past. Part of it is because companies need people so they're buying the people. But other times they're buying the technology because they don't have it in the house, and sometimes they don't know what they're buying." From idea to development happens fast: a 1998 paper in Science on a "perfect mirror," a dielectric (insulating) material that reflects light at any angle with little loss of energy, inspired the founding of a company that wishes to create a hollow fiber whose circumference is lined with the reflector. The fibers may increase capacity 1,000-fold, one company official claims.

Will Anybody Come?

What can be done with all this bandwidth? Lucent estimates that if the growth of networks continues at its current pace, the world will have enough digital capacity by 2010 to give every man, woman and child, whether in San Jose or Sri Lanka, a 100-megabit-a-second connection. That's enough for dozens of video connections or several high-definition television programs. But does each !Kung tribesman in the Kalahari Desert really need to download multiple copies of The Gods Must Be Crazy?

Despite estimates of Internet traffic doubling every few months, some industry watchers are not so sure about infinite demand for infinite bandwidth. Adventis, a Boston-based consultancy, foresees only 15 to 20 percent of home Internet users obtaining broadband access--either cable modems or digital subscriber lines--by 2004. Moreover, storing Web pages on a server will reduce the burden on the network. In the U.S., according to the firm's estimate, nearly 40 percent of existing fiber capacity will go unused in 2004, whereas in Europe almost 65 percent will stay dormant. The notion of a capacity glut is by no means a consensus view, however.

In the end, terabit or petabit networking will probably emerge only once some as yet unforeseen use for the bandwidth reveals itself. Like the World Wide Web, originally a project to help particle physicists more easily share information, it may arrive on a tangent, not from a big media company's focused attempt to repackage networked virtual reality. Vinod Khosla, a venture capitalist with Kleiner Perkins Caufield & Byers, talks of the promise of projects that pool together computers that may be either side by side or distributed across the globe. Metacomputing can download Britney Spears and Fatboy Slim, or it can comb through radio telescope data in search of extraterrestrial life. Khosla sees immense benefit in using this model of networked computing for business, tying together machines to work on, say, the computational fluid dynamics of a 1,000-passenger jumbo jet.

So efforts to pick through the radio emissions from billions and billions of galaxies may yield useful clues about what on earth to do with a network pulsing a quadrillion bits a second.

Further Information:

See for a wealth of coverage on new technologies and on companies involved in optical networking.