The breakup of monopoly telephone companies has left the industry with little solid data on optical network traffic, structure, and capacity. Carriers usually have a reasonable idea of the workings of their own systems, but in a competitive environment they often consider this information proprietary. With no single source of information on national and global optical networks, the industry has turned to market analysts, who rely on data from carriers and manufacturers to formulate an overall view. Unfortunately, analysts cannot get complete information, and the data they do obtain have sometimes been inaccurate. This chapter will analyze this problem and discuss in detail some of the optical networking technology that is out there to fix it [1].

The problem peaked during the bubble, when analysts claimed that Internet traffic was doubling every 3 months or 100 days. Carriers responded by rushing to build new long-haul transmission systems on land and at sea. Only after the bubble burst did it become clear that claims of runaway Internet growth were an Internet myth. The big question now is what is really out there? How far did the supply of bandwidth overshoot the no-longer-limitless demand? All that is clear is that there are no simple answers [1].

The problems start with defining traffic and capacity. If there is an optical fiber glut, why do some calls from New York fail to go through to Paris? One prime reason is that long-haul telephone traffic is separated from the Internet backbone. Longdistance voice traffic has been growing consistently at about 8–10% annually for many years. This enables carriers to predict accurately how much capacity they will need and provision services accordingly. Declining prices and increasing competition have made more capacity available, but the real excess of long-haul capacity is for Internet backbone transmission [1].

Voice calling volume varies widely during the day, with a peak between 10 and 11 a.m., which is about 100 times more than the volume in the wee hours of the morning. Internet traffic also varies during the day, although not nearly as much. It is not just that hackers and programmers tend to work late at night; Internet traffic is much more global than phone calls, and some traffic is generated automatically. It also varies over days or weeks, with peaks about three to four times higher than the norm [1].

Average Internet volume is not as gigantic as is often assumed. Industry analysts estimate the U.S. Internet backbone traffic averaged over a month in late 2004 at about 500 Gbps, less than half the capacity of a single optical fiber carrying 100 dense-wavelength-division multiplexed channels at 10 Gbps each. Most analysts believe the volume of telephone traffic is somewhat lower [1].

No single optical fiber can carry all that traffic because it is routed to different points on the map. Internet backbone systems link major urban centers across the United States. Looking carefully, one can see that the capacity of even the largest intercity routes on the busiest routes is limited to a few 10-Gbps channels, while many routes carry either 622 Mbps (megabits per second) or 2.5 Gbps. That is because some 60 enterprises have Internet backbones. All of them do not serve the same places, but there are many parallel links on major intercity routes [1].

Other factors also keep traffic well below theoretical maximum levels. Like highways, Internet transmission lines do not carry traffic well if they are packed solid. Transmission comes only at a series of fixed data rates, separated by factors of 4, so carriers wind up with extra capacity—like a hamlet that needs a two-lane road to carry a few dozen cars a day. Synchronous optical networks (SONETs) include spare optical fibers equipped as live spares, so that traffic can be switched to them almost instantaneously if service is knocked out on the primary optical fiber [1].

These factors partly explain the industry analysts’ estimated current traffic amounts to only 7–17% of fully provisioned Internet backbone capacity. Typically established carriers carry a larger fraction of traffic than newer ones. Today’s low usage reflects both the division of traffic among many competing carriers and the installation of excess capacity in anticipation of growth that never happened [1].

Carriers’ efforts to leave plenty of room for future growth contribute to horror stories like the one claiming that 97% of long-distance fiber in Oregon lies unused. It sounds bad when an analyst says that cables are full of dark optical fibers, and that only 12% of the available wavelengths are lit on fibers that are in use. But this reflects the fact that the fiber itself represents only a small fraction of system cost. Carriers spend much more money acquiring rights of way and digging holes. Given these economics, it makes sense to add cheap extra fibers to cables and leave spare empty ducts in freshly dug trenches. It is a pretty safe bet that as long as traffic continues to increase, carriers can save money by laying cables containing up to 432 optical fiber strands rather than digging expensive new holes when they need more capacity [1].

Terminal optics and electronics cost serious money, but they can be installed in stages. The first stage is the wavelength division multiplexing (WDM) optics and optical amplifiers needed to light the optical fiber to carry any traffic. The optics typically provides 8–40 channel slots in the erbium amplifier C-band. Transmitter line cards are added as needed to light channels, as little as one at a time. Although some optical fibers in older systems may carry nearly a full load, many carry little traffic. Industry analysts estimate that only 12% of channels are lit in the 12% of optical fibers that carry traffic. The glut of potential capacity is highest in long-haul systems at major urban nodes. According to industry analysts, the potential interconnection capacity into Chicago is 2000 Tbps (terabits per second—trillion bits per second), but only 1.5% of that capacity is lit. The picture is similar in Europe, where 2.0% of potential fiber capacity is lit. Capacity-expanding technologies heavily promoted during the bubble are finding few takers in the new, harsher climate. For example, Nippon Telegraph and Telephone (NTT) is essentially one of only a few customers for transmission in the long-wavelength erbium amplifier L-band, because it allows dense wavelength division multiplexing (DWDM) transmission in zero-dispersionshifted optical fibers installed in NTT’s network [1].

Transoceanic submarine cables have less potential capacity because the numbers of amplifiers that they can power is limited; so is the number of wavelengths per optical fiber. Nonetheless, some regions have far more capacity than they can use. According to industry analysts, the worst glut is on intra-Asian routes, where 1.3 Tbps of capacity is lit, but the total potential capacity with all optical fibers lit and channels used would be 30.8 Tbps. Three other key markets have smaller capacity gluts: transatlantic where 2.9 Tbps are in use and potential capacity is 12.5 Tbps, transpacific where 1.5 Tbps are lit and total potential capacity is 9.0 Tbps, and cables between North and South America, where 275.8 Gbps are lit today, and total potential capacity is 5.1 Tbps. With plenty of fiber available on most routes and some carriers insolvent, announcements of new cables have virtually stopped. Operators in 2002 quietly pulled the plug on the first transatlantic fiber cable, TAT-8, because its total capacity of 560 Mbps on two working pairs was dwarfed by the 10 Gbps carried by a single wavelength on the latest cables [1].

The numbers bear out analyst comments that the optical fiber glut is less serious in metropolitan and access networks. Overcapacity clearly exists in the largest cities, particularly those where competitive carriers laid new cables for their own networks. Yet intracity expansion did not keep up with the overgrowth of the long-haul network. Industry analysts claim that the six most competitive U.S. metropolitan markets had total intracity bandwidth of 88 Gbps—50% less than the total long-haul bandwidth passing through those cities [1].

The real network bottleneck today lies in the access network, but is poorly quantified. The origin of one widely quoted number—that only some 7% of enterprise buildings have optical fiber links—is as unclear as what it covers. Does it cover gas stations as well as large office buildings? Even the results of a recent metropolitan network survey raise questions. It claims that eight cities have enterprise Internet connections totaling less than 6 Gbps, with only 1.6 Gbps from all of Philadelphia—numbers that are credible only if they represent average Internet-only traffic, excluding massive backups of enterprise data to remote sites that do not go through the Internet [1].

Although understanding of the global network has improved since the manic days of the bubble, too many mysteries remain. Paradoxically, the competitive environment that is supposed to allocate resources efficiently also promotes enterprise secrecy that blocks the sharing of information needed to allocate those resources efficiently. Worse, it created an information vacuum eager to accept any purported market information without the skeptical look that would have showed WorldCom’s claims of 3-month doubling to be impossible. Those bogus numbers (together with massive market pumping by the less-savory side of Wall Street) fueled the irrational exuberance that drove the optical fiber industry through the bubble and the bust [1].

Internet traffic growth has not stopped, but its nature is changing. Industry analysts claim that U.S. traffic grew 88% in 2005, down from doubling in 2004. Slower growth rates are inevitable because the installed base itself is growing. An 88% growth rate in 2005 means that the traffic increased 1.7 times the 2004 increase; the volume of increase was larger, but the percentage was smaller because the base was larger [1].

The nature of the global optical fiber network also is changing. In 1995, industry analysts found that just under half the 34.4 million km of cable fiber sold around the world was installed in long-haul and submarine systems. By the end of 2004, the global total reached 804 million km of optical fiber, with 414 million in the United States, and only 27% of the U.S. total in long-haul systems. The long-haul fraction will continue to shrink [1].

Notwithstanding Wall Street pessimism, optical system sales continue today, although far below the levels of the bubble. Industry analysts expect terminal equipment sales to revive first, as the demand for bandwidth catches up with supply and carriers start lighting today’s dark optical fibers. The recovery will start in metro and access systems, with long-haul lagging because it was badly overbuilt. One may not get as rich as one dreamed of during the bubble, but the situation will grow better and healthier in the long-term [1].

So, with the above discussion in mind, let us now look at several optical networking technologies. First, let us start with an overview of the use of digital signal processing (DSP) in optical networking component control. Optical networking applications discussed in this part of the chapter include fiber-optic control loops for erbium-doped fiber amplifiers (EDFA) and microelectromechanical systems (MEMS)-based optical switches. A discussion on using DSP for thermoelectric cooler control is also included [2].