The web is groaning under its own the weight - now there's a
radical plan to rebuild it from the bottom up
ON 18 July 2001, a freight train derailed in the Howard Street tunnel
running beneath downtown Baltimore, spilling 20,000 litres of
hydrochloric acid. The resulting chemical fire destroyed
fibre-optic cables owned by eight major US internet carriers. Moments
later, Verizon Communications, which operates key portions of the
internet's physical infrastructure in the US, lost links to two
operations buildings and several other carriers' networks. For many
hours, internet traffic slowed to a crawl across the entire country.
"That tunnel is basically the I-95 [the main US East Coast highway]
for fibre," one repair contractor told reporters. "It was a
once-in-a-lifetime place for vulnerability."
Eight years on, and events have proved otherwise. A series of
catastrophic failures seems to suggest that the internet is rather
more vulnerable to accidents, earthquakes or misplaced ships' anchors
than people thought. At tens, perhaps hundreds, of places around the
world, the net seems to be hanging by a thread.
These days a major failure has the potential to cause far greater
disruption than in 2001. Yet much of the internet's physical
infrastructure is decades old. It badly needs upgrading, but clearly
we can't just tear up sections of the network and rebuild them from
scratch. Nor is it likely that governments and telecoms companies will
bear the enormous costs of laying extra connections simply to insure
against temporary problems. So how can we make the net more resilient?
Nick McKeown, a computer scientist at Stanford University in
California, thinks he has the answer. He believes the key to a better
net lies with a prosaic black box called a router.
Routers are the internet's traffic controllers. There are millions in
service, linking up the thousands of networks that make up the
internet. They can direct huge flows of traffic for internet service
providers, or just provide connectivity between a handful of
computers. They check the addresses on data packets, direct them to
the right destination and dictate which physical path they take to get
there. When a connection breaks, they play a crucial role in helping
divert data around it.
At the moment, though, routers are part of the problem, not the
solution. For one thing, they can be very slow to find a way around a
blockage, and in the many minutes it often takes, traffic backs up
into jams so huge that much of the data is simply discarded.
Though numerous potential solutions to these problems exist, the other
big sticking point is that there is nowhere to test them. Any update
of router software ought first to be thoroughly tested on a large
network - one that has all the complexity of the internet but which is
physically isolated from it. Yet nothing like that exists.
Even if you could test it, says McKeown, it is very difficult to
actually install new router software. Each router is pre-programmed
according to international standards set 10 or 15 years ago largely by
the manufacturers themselves. They contain proprietary circuits, and
the software controlling the way data packets are routed operates in
set ways, allowing little means for change.
Now McKeown, along with Stanford colleague Guru Parulkar, is
developing the means to solve all these problems at a stroke: a system
that can alter a router's control software on the fly as well as
providing the perfect place to test it safely.
Smoother surfing
Named OpenFlow, their system is already running on Stanford
University's network, and the first commercial products should reach
the market this year. OpenFlow won't solve the problem of cable
bottlenecks or prevent the odd accidental failure, but if the
technology is adopted as McKeown hopes, it will enable the internet to
adapt to changing loads, dynamically altering pathways to cope with
spikes in traffic and giving every surfer a smoother ride, regardless
of earthquakes, terrorists, ships' anchors and so on. "We are trying
to enable a network that continually evolves and improves," says
McKeown.
Anything that makes the internet more resilient should be good news,
and not just for the millions of ordinary people who use it to book
holidays or twitter to their friends. The financial impact of a net
outage can be huge: online commerce is now worth over $7 trillion
annually, representing about 12 per cent of global GDP. A 2005
study by researchers at the Swiss Federal Institute of Technology in
Zurich calculated that cutting off all links to the internet would
cost Switzerland over $3 billion per week - around 1 per cent of its
GDP. And with e-commerce expected to account for 18 per cent of global
GDP by 2010, the impact of failure is set to grow.
Aside from that, critical parts of our infrastructure, such as
power and water utilities, now rely on the internet for
information exchange and remote diagnostics. Banks and stock exchanges
around the world swap financial data via the internet, as well as
using their own networks. Transport systems, too, such as the German
railway system, rely on it to link ticketing and information networks.
In fact, it might seem miraculous, given the internet's growing
traffic density, that outages have not caused more problems. This is
mainly down to the fact that the internet is a scale-free network,
which is another way of saying that while it depends on a few highly
connected nodes, most have just a few connections. That means an
outage in one area has a limited impact elsewhere and it doesn't take
much to adjust traffic flow to keep things moving.
Routers play a key role in making this happen. Normally a router
checks the address on any data packet it receives and sends it on
according to predefined rules held in a set of tables. Two sets of
data going to the same address, say, are usually sent along the same
path. If this path becomes impassable for whatever reason, the router
checks in with its neighbours, finds out which still work, and
calculates the best way to redirect data.
To do this, routers run a complex algorithm, but it can take many
minutes to complete. Because of the problems with testing and updating
new software, technical improvements have come at a glacially slow
rate. Any change must be made very carefully, says Tom Anderson at the
University of Washington in Seattle. "You have to make sure that
you're not doing something that will create problems of its own."
That was highlighted in February, when a small error in a software
update for a router in the Czech Republic spread across the web,
causing traffic to slow to a crawl across the entire internet for over
an hour. This is by no means the first time such a mistake has caused
chaos (see map). Yet there is no large-scale testbed or "virtual
internet" on which to experiment.
In 2005, the US National Science Foundation (NSF) asked a team of
researchers to find a way around this problem. Their solution was
bold: construct a huge new national network, with much the same
complexity as the internet, on which to test and refine novel concepts
until they are ready to be transferred to the real thing. As if that
wasn't ambitious enough, they also wanted to slice up the traffic on
this network. The idea was that each slice could run on the same
infrastructure of routers, switches and cables, but remain isolated
from every other slice. That way thousands of researchers could
experiment with different approaches all at the same time.
The NSF liked the idea enough to stump up over $10 million in start-up
funds for what is now called the Global Environment for Network
Innovations (GENI) project. The new nationwide grid will take many
years, and over $100 million, to complete. Now, though, McKeown and
his colleagues have come up with a plan that will not only allow GENI
to be deployed much more quickly and cheaply, but the project will
largely be able to use existing routers, switches and cables.
The key is OpenFlow. With the cooperation of the manufacturer, a small
OpenFlow program can be added to almost any router, where it acts like
a remote control for the proprietary algorithms and hardware inside.
By creating an interface to the router's flow table - the thing that
specifies the rules for handling traffic - it allows someone to take
control of the way the router directs traffic, to make new routeing
decisions and implement them.
The upshot is that OpenFlow gives software engineers and developers
the ability to create their own routes for data packets, by writing
the algorithms on a regular computer and sending them via a secure
connection to the router. By controlling the flow table, it becomes
straightforward to partition a network into any number of slices, each
isolated from the rest, on which researchers can test or refine their
ideas. With a "multiverse" of virtual networks available for
experiment, it should at last be possible to kick-start the evolution
of the internet.
With a multiverse of virtual networks, it should be possible to
kick-start the evolution of the internet
To speed up the process, McKeown and his team decided to make their
system open source, meaning that the software is free for
redistribution. This should help stimulate new ideas and help get them
deployed more quickly, he says. "You get the benefit of sharing and
building on top, creating a rapid rate of innovation," McKeown says.
"That has never happened in networking."
OpenFlow is already providing internet testbeds on the Stanford
University network, and the team plans to install it on half a dozen
other university networks in the US in the near future. Their aim is
to allow students to experiment and try out new ideas on virtual
networks. With a number of manufacturers on board already, the team
hopes to see OpenFlow-compatible commercial routers, internet switches
or Wi-Fi access points reach the market this year.
The idea so impressed Chip Elliott, GENI's project director, that GENI
is now one of OpenFlow's chief funders. It is a really good way to
open up the network for experimentation and innovation, he says. The
alternatives would be a lot more expensive and take longer to
implement. "What I really like is that they based it all on fast,
cheap, commercial hardware."
Success, however, will depend on convincing the major manufacturers
that the long-term advantages of OpenFlow are worth the short-term
investment. To help persuade them, last year the team at Stanford put
OpenFlow through its paces by installing a "virtual server"
running a shoot-'em-up game on a computer on Stanford's network.
Thanks to router software written using OpenFlow, players equipped
with laptops found that even though they moved between wireless access
points all round the campus, the game play was seamless. "No one lost
connections," McKeown says. Then, while the game was still going on,
the researchers moved the virtual server from Stanford to a machine in
Japan. The game continued without any interruption. "You couldn't even
tell that it had moved. That's the kind of thing you can't do in the
current network."
Beyond this kind of smooth rerouting, OpenFlow should offer some
important benefits for network operators. It could let them alter
their router's rules so that particular kinds of data are sent along
particular routes - to give emails priority over music downloads, say,
or spread traffic over a large number of alternative connections when
one path is broken. "It allows you to add new capabilities, new
features to the network, without having to program inside that
proprietary box," says McKeown. "In essence it is software-defined
networking."
Another key problem that OpenFlow should help address is network
security. After the recent router error in the Czech Republic, a group
of experts took a close look at the software running on routers and
switches. They found that there are vulnerabilities in every version
of every router manufacturer's software, allowing hackers to hijack a
router, say. In other words, the very fabric of the internet itself is
at risk.
Initially, OpenFlow could actually make networks less secure since it
offers a route for attack, admits McKeown. But that should change
rapidly as engineers develop new, more secure versions of router code
that can be tested on existing systems without slowing or interrupting
traffic. Then, when an update is ready to be installed, the fix can be
accomplished simply by programming in the new instructions, rather
than taking the router off-line and reprogramming by hand.
One of the most important benefits of OpenFlow could arise from the
ability to alter the way that data packets travel across the network.
At the moment, emails between two particular computers always take the
same path. Problems arise when any one connection on that path fails.
So a number of research groups are exploring "multipath" routing,
including Gyu Myoung Lee at the Korean Advanced Institute of Science
and Technology in Daejeon. This involves splitting a message into
several packets and sending each one via a different route to its
destination, where they can be recombined. Lee and others are
convinced that by spreading traffic more evenly, this approach will
increase the internet's reliability and reduce congestion. There are
several competing multipath schemes, and with OpenFlow they could all
be tested on the same network to quantify the advantages they offer.
Such a test may not be too far off. This spring, two more
universities, Columbia University in New York city and Georgia
Institute of Technology in Atlanta, have started teaching students
OpenFlow. Meanwhile, electronics manufacturer NEC has announced it
will begin making OpenFlow-enabled routers. Within five years, McKeown
predicts, we could see a thriving community of developers creating
open-source software to redefine how the internet works. He expects
internet data centres to be the movement's advance guard because they
have vast arrays of routers and are used to creating their own
software. "If in those same five years the net itself becomes
software-defined," McKeown says, "well, that would be nice, too."
Bennett Daviss is a science writer based in New Hampshire
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