June 2001

Breaking the Metro Bottleneck

Continued from page 3

By Jeff Hecht

High-Fiber Diet

Merely weaving more fiber into the metro network won't solve all the problems that crop up in urban areas. Today's systems rely on a sometimes awkward mix of electronic and optical technology. Tiny lasers launch data-bearing light beams into optical fibers. At the other end, the light strikes a photosensor, which converts the on and off flashes into an electrical signal that electronic switches direct to its proper destination. Such electronic switching works fine at the modest speeds of 2.5 gigabits per second that are now in common metro use.

But start cranking up the data rate, and electronic circuitry has a tough time keeping up with the potential of optical networking. The solution: all-optical switches that redirect light signals without converting them to electrons. The higher the bit rate, the greater the all-optical advantage. Indeed, when you get to 40 gigabits per second, "there's no alternative to all-optical" switching, says Lawrence Gasman, president of Communications Industry Researchers.

Getting to an all-optical metro system isn't going to be simple, though, because it will require the construction of new networks. For established phone companies, the burden may not be crushing, since most existing underground urban cables are threaded through buried ducts, and phone companies can often pull out old cables and pull in new ones-as they did when replacing copper with fiber cables in the 1980s. New companies, on the other hand, have to build complete new networks. One such company, Metromedia Fiber Network, plans to expand beyond its New York City base and install almost six million kilometers of fiber in 67 cities in North America and Europe by 2004.

But whether they are laying entirely new networks or trying to modify existing systems to upgrade their performance, the builders and operators of the metro loops that knit together the most concentrated populations of homes are performing a crucial task. The backbone and the corporate networks that flank the metro loop get faster every year. If the metro bottleneck is not broken, broadband will remain little more than a clever idea that some techies once had.