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In today’s Internet, data travelling through optical fibers as beams of light have to be converted to electrical signals for processing. By dispensing with that conversion, a new network design could increase Internet speeds 100-fold.
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The heart of the Internet is a network
of high-capacity optical fibers that spans continents. But while optical
signals transmit information much more efficiently than electrical signals,
they’re harder to control. The routers that direct traffic on the Internet
typically convert optical signals to electrical ones for processing, then
convert them back for transmission, a process that consumes time and energy.
In recent years, however, a group of MIT
researchers led by Vincent Chan, the Joan and Irwin Jacobs Professor of
Electrical Engineering and Computer Science, has demonstrated a new way of
organizing optical networks that, in most cases, would eliminate this
inefficient conversion process. As a result, it could make the Internet 100 or
even 1,000 times faster while actually reducing the amount of energy it
consumes.
One of the reasons that optical data
transmission is so efficient is that different wavelengths of light loaded with
different information can travel over the same fiber. But problems arise when
optical signals coming from different directions reach a router at the same
time. Converting them to electrical signals allows the router to store them in
memory until it can get to them. The wait may be a matter of milliseconds, but
there’s no cost-effective way to hold an optical signal still for even that
short a time.
Chan’s approach, called “flow
switching,” solves this problem in a different way. Between locations that
exchange large volumes of data—say, Los Angeles
and New York City—flow
switching would establish a dedicated path across the network. For certain
wavelengths of light, routers along that path would accept signals coming in
from only one direction and send them off in only one direction. Since there’s
no possibility of signals arriving from multiple directions, there’s never a
need to store them in memory.
Reaction time
To some extent, something like this already happens in today’s Internet. A large
Web company like Facebook or Google, for instance, might maintain huge banks of
Web servers at a few different locations in the United States. The servers might
exchange so much data that the company will simply lease a particular
wavelength of light from one of the telecommunications companies that maintains
the country’s fiber-optic networks. Across a designated pathway, no other
Internet traffic can use that wavelength.
In this case, however, the allotment of
bandwidth between the two endpoints is fixed. If for some reason the company’s
servers aren’t exchanging much data, the bandwidth of the dedicated wavelength
is being wasted. If the servers are exchanging a lot of data, they might exceed
the capacity of the link.
In a flow-switching network, the
allotment of bandwidth would change constantly. As traffic between New York and Los
Angeles increased, new, dedicated wavelengths would be
recruited to handle it; as the traffic tailed off, the wavelengths would be
relinquished. Chan and his colleagues have developed network management
protocols that can perform these reallocations in a matter of seconds.
In a series of papers published over a
span of 20 years—the latest of which will be presented at the OptoElectronics
and Communications Conference in Japan next month—they’ve also performed
mathematical analyses of flow-switched networks’ capacity and reported the
results of extensive computer simulations. They’ve even tried out their ideas
on a small experimental optical network that runs along the Eastern Seaboard.
Their conclusion is that flow switching
can easily increase the data rates of optical networks 100-fold and possibly
1,000-fold, with further improvements of the network management scheme. Their
recent work has focused on the power savings that flow switching offers: In
most applications of information technology, power can be traded for speed and
vice versa, but the researchers are trying to quantify that relationship. Among
other things, they’ve shown that even with a 100-fold increase in data rates,
flow switching could still reduce the Internet’s power consumption.
Growing appetite
Ori Gerstel, a principal engineer at Cisco Systems, the largest manufacturer of
network routing equipment, says that several other techniques for increasing
the data rate of optical networks, with names like burst switching and optical
packet switching, have been proposed, but that flow switching is “much more
practical.” The chief obstacle to its adoption, he says, isn’t technical but
economic. Implementing Chan’s scheme would mean replacing existing Internet
routers with new ones that don’t have to convert optical signals to electrical
signals. But, Gerstel says, it’s not clear that there’s currently enough demand
for a faster Internet to warrant that expense. “Flow switching works fairly
well for fairly large demand—if you have users who need a lot of bandwidth and
want low delay through the network,” Gerstel says. “But most customers are not
in that niche today.”
But Chan points to the explosion of the
popularity of both Internet video and high-definition television in recent years.
If those two trends converge—if people begin hungering for high-definition
video feeds directly to their computers—flow switching may make financial
sense. Chan points at the 30-inch computer monitor atop his desk in MIT’s
Research Lab of Electronics. “High resolution at 120 frames per second,” he
says: “That’s a lot of data.”
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