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suppose it o ers a separate service---like phone or television---that
competes with Internet services. If it can treat some packets better
than others, it has the means to an unfair advantage over its own
rivals, or its partners', or its subsidiaries'.
The idea that the Internet should be fair---that it shouldn't pick
favorites among users, service providers, applications, and types of
content---is generally known as net neutrality. And it's a principle
that has been much in the news lately, after its apparent violation
by Comcast, the second-largest ISP in the United States.
Last summer, it became clear that Comcast was intentionally
slowing down peer-to-peer tra c sent over its network by programs
using the popular file-sharing protocol BitTorrent. The Federal
Communications Commission agreed to investigate, in a set of
hearings held at Harvard and Stanford Universities in early 2008.
It wasn't BitTorrent Inc. that had complained to the FCC, but
rather a company called Vuze, based in Palo Alto, CA, which uses
the BitTorrent protocol---perfectly legally---to distribute high-
definition video over the Internet. As a video distributor, Vuze is
in competition, however lopsided, with Comcast. By specifically
degrading the performance of BitTorrent tra c, Vuze argued, Com-
cast was giving itself an unfair advantage over a smaller rival.
At the Harvard hearing, Comcast executive vice president
David Cohen argued that his company had acted only during
periods of severe congestion, and that it had interfered only with
tra c being uploaded to its network by computers that weren't
simultaneously performing downloads. That was a good indica-
tion, Cohen said, that the computers were unattended. By slowing
the uploads, he said, Comcast wasn't hurting the absent users, and
it was dramatically improving the performance of other applica-
tions running over the network.
Whatever Comcast's motivations may have been, its run-in with
Vuze graphically illustrates the conflict between congestion man-
agement and the principle of net neutrality. "An operator that is just
would exceed network capacity by 2010. Andrew Odlyzko, who
runs the Minnesota Internet Tra c Studies program at the Uni-
versity of Minnesota, believes that the growth rate is closer to 50
percent. At that rate, he says, expected improvements in standard
network equipment should keep pace with tra c increases.
But if the real rate of traffic growth is somewhere between
Nemertes's and Odlyzko's estimates, or if high-definition video
takes o online, then tra c congestion on the Internet could
become much more common. And the way that congestion is
relieved will have implications for the principles of openness and
freedom that have come to characterize the Internet.
WHOSE BITS WIN?
The Internet is a lot like a highway, but not, contrary to popular
belief, a superhighway. It's more like a four-lane state highway with
tra c lights every five miles or so. A packet of data can blaze down
an optical fiber at the speed of light, but every once in a while it
reaches an intersection where it has the option of branching o
down another fiber. There it encounters a box called an Internet
router, which tells it which way to go. If tra c is light, the packet
can negotiate the intersection with hardly any loss of speed. But if
too many packets reach the intersection at the same time, they have
to queue up and wait for the router to usher them through. When
the wait gets too long, you've got congestion.
The transmission control protocol, or TCP---one of the Internet's
two fundamental protocols---includes an algorithm for handling
congestion. Basically, if a given data link gets congested, TCP tells
all the computers sending packets over it to halve their transmis-
sion rates. The senders then slowly ratchet their rates back up---until
things get congested again. But if your computer's transmission
rate is constantly being cut in half, you can end up with much less
bandwidth than your broadband provider's ads promised you.
Sometimes that's not a problem. If you're downloading a video
to watch later, you might leave your computer for a few hours and
not notice 10 minutes of congestion. But if you're using streaming
audio to listen to a live World Series game, every little audio pop or
skip can be infuriating. If a router could just tell which kind of tra c
was which, it could wave the delay-sensitive packets through and
temporarily hold back the others, and everybody would be happy.
But the idea that an Internet service provider (ISP) would make
value judgments about the packets traveling over its network makes
many people uneasy. The Internet, as its name was meant to imply,
is not a single network. It's a network of networks, most of which the
average user has never heard of. A packet traveling long distances
often has to traverse several networks. Once ISPs get in the business
of discriminating between packets, what's to prevent them from
giving their own customers' packets priority, to the detriment of
their competitors'? Suppose an ISP has partnered with---or owns---a
Web service, such as a search engine or a social-networking site. Or
GLOBAL INTERNET TRAFFIC
Petabytes per month
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