10 August 2016
The bandwidth bottleneck that is throttling the Internet
Researchers are scrambling to repair and
expand data pipes worldwide — and to keep the information revolution from
grinding to a halt.
On
19 June, several hundred thousand US fans of the television drama Game
of Thrones went online to watch an eagerly awaited episode — and
triggered a partial failure in the channel's streaming service. Some 15,000
customers were left to rage at blank screens for more than an hour.
The
channel, HBO, apologized and promised to avoid a repeat. But the incident was
just one particularly public example of an increasingly urgent problem: with
global Internet traffic growing by an estimated 22% per year, the demand for
bandwidth is fast outstripping providers' best efforts to supply it.
Although
huge progress has been made since the 1990s, when early web users had to use
dial-up modems and endure 'the world wide wait', the Internet is still a global
patchwork built on top of a century-old telephone system. The copper lines that
originally formed the system's core have been replaced by fibre-optic cables
carrying trillions of bits per second between massive data centres. But service
levels are much lower on local links, and at the user end it can seem like the
electronic equivalent of driving on dirt roads.
The
resulting digital traffic jams threaten to throttle the information-technology
revolution. Consumers can already feel those constraints when mobile-phone
calls become garbled at busy times, data connections slow to a crawl in crowded
convention centres and video streams stall during peak viewing hours. Internet
companies are painfully aware that today's network is far from ready for the
much-promised future of mobile high-definition video, autonomous vehicles, remote surgery,
telepresence and interactive 3D virtual-reality gaming.
That
is why they are spending billions of dollars to clear the traffic jams and
rebuild the Internet on the fly — an effort that is widely considered to be as
crucial for the digital revolution as the expansion of computer power. Google has
partnered with 5 Asian telecommunication companies to lay an 11,600-kilometre,
US$300-million fibre-optic cable between Oregon, Japan and Taiwan that started
service in June. Microsoft and Facebook are laying another cable across the
Atlantic, to start service next year. “Those companies are making that
fundamental investment to support their businesses,” says Erik Kreifeldt, a
submarine-cable expert at telecommunications market-research firm TeleGeography
in Washington DC. These firms can't afford bottlenecks.
Laying
new high-speed cable is just one improvement. Researchers and engineers are
also trying several other fixes, from speeding up mobile networks to
turbo-charging the servers that relay data around the world.
The fifth generation
For
the time being, at least, one part of the expansion problem is comparatively
easy to solve. Many areas in Europe and North America are already full of 'dark
fibre': networks of optical fibres that were laid down by over-optimistic
investors during the Internet bubble that finally burst in 2000, and never used.
Today, providers can often meet rising demand simply by starting to use some of
this dark fibre.
But
such hard-wired connections don't help with the host of mobile phones, fitness trackers, virtual-reality
headsets and other gadgets now coming online. Data traffic from
mobile devices is increasing by an estimated 53% per year — most of which will
end up going through mobile-phone towers, or 'base stations', whose coverage is
already spotty, and whose bandwidth has to be shared by thousands of users.
The
quality is spotty, as well. First-generation mobile-phone networks, introduced
in the 1980s, used analogue signals and are long gone. But second-generation
(2G) networks, which added digital services such as texting in the early 1990s,
still account for 75% of mobile subscriptions in Africa and the Middle East,
and are only now being phased out elsewhere. As of last year, the majority of
mobile-phone users in Western Europe were on 3G networks, which were launched
in the late 1990s to allow for more sophisticated digital services such as
Internet access.
The
most advanced commercial networks are now on 4G, which was introduced in the
late 2000s to provide smartphones with broadband speeds of up to 100 megabits
per second, and is now spreading fast. But to meet demand expected by the
2020s, say industry experts, wireless providers will have to start deploying
fifth-generation (5G) technology that is at least 100 times faster, with top
speeds measured in tens of billions of bits per second.
The
5G signals will also need to be shared much more widely than is currently
feasible, says Rahim Tafazolli, head of the Institute for Communication Systems
at the University of Surrey in Guildford, UK. “The target is how can we support
a million devices per square kilometre,” he says — enough to accommodate a
burgeoning 'Internet of Things' that will range from networked household
appliances to energy-control and medical-monitoring systems, and autonomous
vehicles (see'Bottleneck engineering').
The
transition to 5G, like those to 3G and 4G before it, is being coordinated by an
industry consortium that has retained the name Third Generation Partnership
Project (3GPP). Tafazolli is working with this consortium to test a technique
known as multiple-input, multiple-output (MIMO) — basically, a way to make each
radio frequency carry many streams of data at once without letting them mix
into gibberish. The idea is to put multiple antennas on both transmitter and
receiver, creating many ways for signals to leave one and arrive at the other.
Sophisticated signal processing can distinguish between the various paths, and
extract independent data streams from each.
MIMO
is already used in Wi-Fi and 4G networks. But the small size of smartphones
currently limits them to no more than four antennas each, and the same number
on base stations. So a key goal of 5G research is to squeeze more antennas onto
both.
Big
wireless companies have demonstrated MIMO with very high antenna counts in the
lab and at trade shows. At the Mobile World Congress in Barcelona, Spain, in
February, equipment-maker Ericsson ran live indoor demonstrations of a
multiuser massive MIMO system, using a 512-element antenna to transmit 25 gigabits
per second between a pair of terminals, one stationary and the other moving on
rails. The system is one-quarter of the way to the 100-gigabit 5G target, and
it transmits at 15 gigahertz, part of the high-frequency band planned for 5G.
Japanese wireless operator NTT DoCoMo is working with Ericsson to test the
equipment outdoors, and Korea Telecom is planning to demonstrate 5G services
when South Korea hosts the next Winter Olympics, in 2018.
Another
approach is to make the devices much more adaptive. Instead of operating on a
single, hard-wired set of frequencies, a mobile device could use what is
sometimes called cognitive radio: a device that uses software to switch its
wireless links to whatever radio channel happens to be open at that moment.
That would not only keep data automatically moving through the fastest
channels, says Tafazolli, but also improve network resilience by finding ways
to route around failure points. And, he says, it's much easier to upgrade performance
by replacing software than by replacing hardware.
Meanwhile,
a crucial policy challenge for the 5G transition is finding a radio spectrum that offers adequate bandwidth and
coverage. International agreements have already allocated almost
every accessible frequency to a specific use, such as television broadcasting,
maritime navigation or even radio astronomy. So final changes will have to wait
for the 2019 World Radiocommunication Conference. But the US Federal
Communications Commission (FCC) is trying to get a head start by auctioning off
frequencies below 1 gigahertz to telecommunications companies. Once reserved
for broadcast television because they are better than higher frequencies at
penetrating walls and other obstructions — but no longer needed after
television's shift to digital — these low frequencies are particularly
attractive for serving sparsely populated areas, says Tafazolli: only a few
base stations would be required to provide broadband service to households and
driving data to autonomous cars on motorways.
Other
bands in the 1–6-gigahertz range could be opened up for 5G use as 2G and 3G
technologies are phased out. But the best hope for dense urban areas is to
exploit frequencies above 6 gigahertz, which are currently little-used because
they have a very short range. That would require 5G base stations up to every
200 metres in dense urban areas, one-fifth the spacing typical of urban 4G
networks. But the FCC considers the idea promising enough that on 14 July, it
formally approved opening these frequencies for high-speed, fast-response
services. Ofcom, the UK regulatory body, is considering similar steps.
Companies
are particularly interested in these higher frequencies as a way to extend 5G
technology for other uses. In the United States, wireless carrier Verizon and a
consortium of equipment-makers including Ericsson, Cisco, Intel, Nokia and
Samsung have tested 28-gigahertz transmission at sites in New Jersey,
Massachusetts and Texas. The system uses 5G technology to deliver data at 1
gigabit per second, and Verizon is adapting it for use in fixed wireless
connections to homes, which it plans to test next year. The company has been
pushing fixed wireless as an alternative to wired connections, because
connection costs are much lower.
Bigger pipes
“When
I take out my cell phone, everyone thinks of it as a wireless communications
device,” says Neal Bergano, chief technology officer of TE SubCom, a
submarine-cable manufacturer based in Eatontown, New Jersey. Yet that is only
part of the story, he says: “Users are mobile, but the network isn't mobile.”
When someone uses their phone, its radio signal is converted at the nearest
base station to an optical signal that then has to travel to its destination
through fixed fibre optics.
These
flexible glass data channels have been the backbone of the global telecommunications network for
more than a quarter of a century. Nothing can match their bandwidth: today, a
single hair-thin fibre can transmit 10 terabits (trillion bits) per second
across the Atlantic. That is the equivalent of 25 double-layer Blu-ray Discs
per second, and is 30,000 times the capacity of the first transatlantic fibre
cable, laid in 1988. Much of that increase came when engineers learned how to
send 100 separate signals through a single fibre, each at its own wavelength.
But as traffic continues to increase over heavily used routes, such as New York
to London, that approach is coming up against some hard limits: distortion and
noise that inevitably build up as light passes along thousands of kilometres of
glass have made it effectively impossible to send more than 100 gigabits per
second on a single wavelength.
To
overcome that limit, manufacturers have developed a new type of fibre. Whereas
standard fibres send the light through a 9-micrometre-wide core of ultrapure
glass running down the middle, the newer design spreads the light over a larger
core area at lower intensity, reducing noise. The trade-off is that the new
fibres are more sensitive to bending and stretching, which can introduce
errors. But they work very well in submarine cables, because the deep sea provides
a benign, stable environment that puts little strain on the fibre.
Last
year, networking-systems firm Infinera in Sunnyvale, California, sent
single-wavelength signals at 150 gigabits per second through a large-area fibre
for 7,400 kilometres — more than 3 times the distance possible with a standard
fibre, and easily enough to cross the Atlantic. They also transmitted
200-gigabit-per-second signals a shorter distance.
“Digital traffic jams threaten to throttle the
information-technology revolution.”
The
highest-capacity commercial submarine cable now in service is the
60-terabit-per-second FASTER system that opened in June between Oregon and
Japan. It sends 100-gigabit-per-second signals on 100 wavelengths in each of 6
pairs of large-core fibres. But in late May, Microsoft and Facebook jointly
announced plans to beat it with MAREA: a large-area fibre cable spanning the
6,600 kilometres between Virginia and Spain. When completed in October 2017,
the cable will link the two companies' data centres on opposite sides of the
Atlantic at 160 terabits per second.
Another
approach to reducing performance-limiting noise was demonstrated last year by a
group at the University of California, San Diego. Fibre-optic systems normally
use separate lasers for each wavelength, but tiny, random variations can
generate noise. Instead, the group used a technique known as a frequency comb
to generate a series of uniformly spaced wavelengths from a single laser (E. Temprana et al. Science 348, 1445–1448; 2015). “It worked like a charm” to reduce
noise, says group member Nikola Alic, an electrical engineer. With further
development, he says, the approach could double the data rate of fibre-optic
systems.
Time of flight
Impressive
bandwidth is useful, but promptness also matters. Human speech is so sensitive
to interruption that a delay of one-quarter of a second can disturb a phone or
video conversation. Video requires a fixed frame rate, so streaming video
stalls when its input queue runs dry. To overcome such problems, FCC rules
allow special codes that give priority passage for packets of data carrying
voice calls or video frames, so that they flow quickly and uniformly through
the Internet.
New
and emerging services including telerobotics, remote surgery, cloud computing
and interactive gaming are also sensitive to network responsiveness. The time
it takes for a signal to make a round trip between two terminals, often called
latency, depends largely on distance — a reality that shapes the geography of
the Internet. Even though data travel through fibre-optic cable at 200,000
kilometres per second, two-thirds the velocity of light in the open air, a
person tapping a key in London would still need 86 milliseconds to get a
response from a data centre in San Francisco, 8,600 kilometres away — a delay
that would make cloud computing crawl.
Emerging
mobile applications require both broad bandwidth and low latency. Autonomous
cars, for example, need real-time data on their environment to warn them about
hazards, from potholes to accidents ahead. Conventional cars are becoming
wireless nerve centres, needing low latency for 'hands-free' voice-control
systems.
A
potentially huge challenge is the emergence of 3D virtual-reality systems.
Interactive 3D gaming requires data to travel at 1 gigabit per second — 20
times the speed of a typical video feed from a Blu-Ray Disc. But most
crucially, the image must be rewritten at least 90 times per second to keep up
with users turning their heads to watch the action, says computer scientist
David Whittinghill of Purdue University in West Lafayette, Indiana. If the data
stream slips behind, the user gets motion sickness. To keep that from
happening, Whittinghill has installed a special 10-gigabit-per-second fibre
line to his virtual-reality lab.
To
speed up responses, big Internet companies such as Google, Microsoft, Facebook
and Amazon store replicas of their data in multiple server farms around the
world, and route queries to the closest. Video cached at a local data centre is
what allows viewers to fast-forward as if the file was stored on a home device,
says Geoff Bennett, director of solutions and technology for Infinera. But the
proliferation of these data centres is also one of the biggest drivers of
bandwidth demand, he says: vendors' efforts to synchronize private data centres
around the world now consume more bandwidth than public Internet traffic. The
Microsoft–Facebook cable is being built expressly for this purpose (see 'The submarine web').
“Users are mobile, but the network isn't mobile.”
So
far, most data centres are where the customers and cables are: in North
America, Europe and east Asia. “Many parts of the world still rely on remote
access to content that is not stored locally,” says Kreifeldt. South America
has few data centres, he says, so much of the content comes from well-wired
Miami, Florida: traffic between Chile and Brazil might be routed through Miami
to save money, but at a cost in latency. The same problem plagues the Middle
East, where 85% of international traffic must travel to centres in Europe. That
is changing, says Kreifeldt, but progress is slow. Amazon Web Services launched
its first cloud data centre in India this year, in Mumbai; it has had a similar
centre in São Paulo, Brazil, since 2011.
Internal
communications
Bandwidth
is also crucial on the very smallest scale: on and between the chips in the
banks of servers in a data centre. Expanding the flow here can help information
to move more quickly within the data centres and get out to users faster. Chip
clock speeds — how fast the chip runs — flat-lined at a few gigahertz several
years ago, because of heating problems. The most practical way to speed up
processors significantly is to divide the operations that they perform between
multiple 'cores': separate microprocessors operating in parallel on the same
chip. That requires high-speed connections within the chip — and one way to
make them is with light, which can move data faster than electrons can.
The
biggest obstacle has been integrating microscale optics with silicon
electronics. After years of research on 'silicon photonics', engineers have yet
to find a way to efficiently generate light from silicon, a key step in optical
information processing. The best semiconductor light sources, such as indium
phosphide, can be bonded to silicon chips, but are very difficult to
grow directly on silicon, because their atoms are spaced differently. Optical
and electronic components have been integrated on indium phosphide, but so far
only on a small scale.
In
an effort to scale up photonic integration to a commercial level, the United
States last year launched the American Institute for Manufacturing Integrated
Photonics in Rochester, New York, which is supported by $110 million from
federal agencies and $502 million from industry and other sources. Its target
is to develop an efficient technology to make integrated photonics for
high-speed applications, including optical communications and computing.
Separately,
a Canadian-funded team earlier this year demonstrated a photonic integrated
circuit with 21 active components that could be programmed to perform 3
different logic functions (W. Liuet al. Nature
Photon. 10, 190–195; 2016).
That's an important step for photonic microprocessors, comparable in complexity
to the first programmable electronic chips that opened the door to
microcomputers. “Compared to current electronics, it's simple, but compared to
photonic integrated circuits it is quite complicated,” says study co-author
Jianping Yao, an electrical engineer at the University of Ottawa in Canada.
Further
development could lead to varied applications. For example, Yao says that after
the chip is optimized for manufacture, it could convert a 5G smartphone signal
received at a base station into an analogue optical signal, which could be
transmitted by fibre optics to a central facility, and then digitized.
The
quest for faster chips, like other parts of the Internet problem, is a daunting
challenge. But researchers such as Bergano see a lot of potential for
improvements. After 35 years of working on fibre optics, he says, “I remain a
complete optimist when I think about the future.
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