Doug: IP will result in Traffic GRIDLOCK: N. Y. TIMES:
Multimedia Transmissions Drive Net Toward Gridlock
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nytimes.com
August 23, 1999
Multimedia Transmissions Drive Net Toward Gridlock
By SARA ROBINSON
Like a nation's highway system, the Internet has
traffic rules that prevent chaos and gridlock. But an
increasingly popular type of multimedia traffic is
turning out to be a cyber road hog that flouts the rules
and creates traffic jams.
This scofflaw traffic, known as streaming media, is
widely hailed as the future of home entertainment,
capable of eventually delivering high-quality audio and
video programming over the Internet.
Unfortunately, network experts warn, it may drive
everyone else off the road.
Streaming media is analogous to broadcast media in
that the audio or video material is produced as soon as
a computer receives the data over the Internet. The
problem is that the streaming data does not respond to
network congestion in the way other Internet traffic
does.
When a computer sending conventional data encounters
congestion, it significantly slows its own transmission
rate, but a computer sending streaming data will reduce
the flow only slightly. So if streaming traffic competes
with conventional traffic for the same congested strip of
roadway, the streaming traffic, like some VIP
motorcade, assumes the right of way and lets all other
data traffic pile up.
The difference, said Van Jacobson, chief scientist for
Cisco Systems Inc., a leading maker of Internet traffic
routers, is that conventional traffic "is polite; this stuff
is impolite."
"People writing software for that traffic -- they don't
care," Jacobson said of streaming media. "In the long
term, it's a problem."
By its very nature, streaming media has to flow
continuously to the user's computer, so it cannot follow
the same traffic rules as conventional data. But even so,
it is possible for packets of streaming data to interact
civilly with other traffic on the Internet. The reason they
do not, Jacobson said, is that streaming media
providers have no incentive to comply with traffic
rules.
Today, he said, "if Real Networks is polite and
Microsoft isn't, then Real looks crummy."
Even elbowing all other data aside, today's streaming
media produces a very low quality of entertainment
most of the time.
Much of that lack of quality today is a result of slow
modems at the user's end. In three to five years, when
cable modems and souped-up digital telephone lines
are expected to be common, most Internet users may be
listening to live Webcasts or playing high-quality radio
on their computers. In 10 years, movies and
commercial television might very well be carried over
Internet channels.
This increasing demand will add vast amounts of
streaming traffic to the Internet and could lead to what
Jacobson calls "congestion collapse" -- the Internet
equivalent of gridlock.
Internet service providers are also concerned.
Tony Blake, vice president for marketing and business
development for AT&T Labs Research, calls the trend
disturbing, adding, "What people are saying is, 'If my
stuff gets through, that's all I care about."' He said
AT&T and other Internet service providers were
pressuring the producers of streaming media to head off
the problem before it grows out of control.
Streaming media traffic is also of growing concern to
the Internet Engineering Task Force, an industry group
that is the closest thing the Internet has to a governing
technical body. Jacobson, an active task force
participant, said the group has not yet formally
addressed the issue, because "it's not big enough to kill
the Net."
Not yet anyway. But a number of Internet service
providers are getting nervous.
Jacobson said he would like to see streaming media use
congestion controls that are compatible with those used
for conventional data-packet traffic.
Today, according to measurements by the National
Laboratory for Applied Network Research at the
University of California at San Diego, none of the
existing streaming media providers are using such
controls.
Real Networks, the largest streaming media provider,
declined to respond to the growing criticism, although a
spokesman, Jay Wampold, said the company was trying
to address congestion problems. Over the last year, he
said, Real Networks had installed a network of
computers for delivering the company's broadcasts that
bypasses the Internet's main traffic routes.
Kevin Unangst, lead product manager for Windows
Media, the streaming media division at Microsoft
Corp., said the company was working with network
companies to route its streaming data around the
Internet's main arteries.
"We know bandwidth and optimizing bandwidth is a
huge, huge issue," Unangst said, using an industry term
for transmission capacity, "and we're covering all the
bases."
But Jacobson said that while actions like those taken by
Real Networks and Microsoft might help, they would
not resolve the problem. The bottlenecks are not on the
main thoroughfares, he said, but on the side streets and
access roads.
"As you get out to the edge of network, closer to users,
that's where the bandwidth gets limited," he said.
While cable modems and digital subscriber lines will
increase bandwidth to the home, a truly significant
increase in Internet bandwidth would require ripping
out 300 million copper wires and replacing them with
fiber.
"That's not going to happen fast," Jacobson said.
The remedy, experts say, lies in providing incentives
for streaming media providers to comply with traffic
rules.
With the proper incentive structure in place, streaming
material from both Microsoft and Real Networks
would look slightly worse than it does now, Jacobson
said, but at least the competition for bandwidth would
be fairer.
As a standards-setting organization, the Internet
Engineering Task Force does not have legal authority to
force software developers to adopt congestion-control
measures.
But standards, which enable all the computers linked to
the Internet to talk to one another, can sometimes be
used to discourage disruptive behavior.
"It's the tragedy of the commons," said Sally Floyd, a
researcher at the AT&T Center for Internet Research at
the International Computer Science Institute in
Berkeley, Calif. "Only with the right incentive structure
do the right things happen."
The "tragedy of the commons" is an example from
economic game theory. If a group of farmers must graze
their cattle in the same small patch of grass, or
commons, it is in the farmers' collective interest not to
overgraze, lest all the grass die out and all the cows
starve. The problem is that it is in each individual
farmer's interest to act counter to the common good.
Ordinary Internet traffic -- e-mail and data
transmissions to and from Web sites, for example --
follows a basic set of traffic laws known as the
transmission control protocol, or TCP.
Since the late 1980s, when rising Net traffic led to
severe congestion problems, TCP has included a
congestion-control mechanism that instructs a
transmitting computer to slow the data flow by half as
soon as the data it is sending encounters congestion.
Only when the congestion clears does the data speed up
again.
"What's interesting is that congestion itself is
effectively the error signal that gives the sender the
feedback to speed up or slow down," said Robert J.
Berger, president of Internet Bandwidth Development,
a consulting firm in Saratoga, Calif. "It means that there
will almost always be at least a bit of congestion, but
that's OK."
But it is not OK when traffic that conforms to TCP runs
into traffic that does not follow those same rules. When
the point of congestion is reached, TCP traffic cuts its
sending rate in half. But streaming traffic just barrels
through the stoplights. This in turn creates more
congestion, which further slows the law-abiding traffic.
Streaming media traffic "needs to back off," said Scott
Shenker, head of the AT&T Center for Internet
Research in Berkeley. "I think most researchers feel it's
a flaw in the Internet architecture that there's no way to
deal with this."
Both Shenker and Jacobson believe the solution to the
streaming media problem is to build incentives into the
architecture to encourage good behavior. But they have
very different ideas of what form those incentives
should take.
Shenker prefers to plant a mechanism within Internet
routers that he calls "fair queuing," which would force
packets sent from different sources to wait their turn to
be sent.
Jacobson's proposal, developed with Ms. Floyd in
1989 and only now being tested in Cisco routers, uses a
kind of virtual penalty box. When the router
experiences congestion, it takes a random sample of its
traffic. If a certain host computer is overrepresented in
that sample, its packets are placed at the end of the line.
This creates the right incentive structure, he said,
because the Internet service providers do not have to
persuade Real Networks or any other company to obey
the rules. Rather, he says, "The customers do instead,
because the quality" of their audio and video "gets
really crummy."
Fair queuing and penalty boxes rely on software fixes
to change the incentives. Another approach, favored by
many service providers, is to create economic
incentives for fair sharing of the roadways. The basic
idea is that heavy users should be paying for the extra
bandwidth that they consume.
This model, known as differential service, is already
being deployed on the Internet. But there are many
questions about how it should be adapted to streaming
media -- especially about who should pay.
"The real puzzle about streaming media is who is going
to make the money -- if we knew this, then we could
answer a lot of the technical questions," said David
Clark, a senior research scientist at the Massachusetts
Institute of Technology's Laboratory for Computer
Science.
Whatever solution is eventually adopted, the streaming
media problem is certain to be resolved, these experts
say.
"An Internet that's growing and can handle streaming
media is in everyone's interests," said Blake of AT&T
Labs. "We poke each other with sharp sticks all the
time, but slowly we move forward."
Related Sites
These sites are not part of The New York Times on the Web, and The
Times has no control over their content or availability.
Cisco Systems Inc.
Real Networks
Microsoft
AT&T Labs Research
Internet Engineering Task Force
National Laboratory for Applied Network
Research
AT&T Center for Internet Research
Internet Bandwidth Development
Massachusetts Institute of Technology's
Laboratory for Computer Science
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essage #15738 from Doug at Dec 14 1999 8:15PM
Z.O: I appreciate your research. I have no doubts that outside the USA, ATM is alive and well.
In the USA , ATM was popular with Carriers and Enterprises that needed speed, reliability and data security. In the last few Quarters, IP has been gaining share
some claim at the expense of ATM(NN). It could be due to a number of factors. In brief in the USA the ATM picture is not quite clear. The question raised concerning
the U.S mkt are :
a: Existing Sales growth of ATM
b: Forecast growth of ATM switches vrs IP.
c: Forecast ATM switch capacity vrs existing demand.
d: Perceived long term trend for ATM vrs pure IP.
If NN is deciding to go it alone, I would like to know how NN can respond if ATM becomes less popular in the USA. |
