Austin, Texas
IT鈥橲 NOT just boy racers on tarmac roads who yearn for more speed. On the
information superhighway more speed means more words, more pictures, more
sound鈥攁nd more entertainment all round. Yet everyone who has been there
knows that there are bottlenecks galore. You can avoid the worst congestion by
navigating the Net at a time when most users鈥攁nd that means
Americans鈥攁re asleep. But there is another bottleneck closer to home: it
runs from the back of your computer to the local telephone exchange. On this
鈥渋nformation driveway鈥�, speed is limited by the trusty modem.
True, these devices have been getting faster over the years, as competition
between modem makers has hotted up. Last September, Rockwell Semiconductor
Systems announced that it would launch a set of modem chips late this year that
would squirt 56 kilobits per second (kbps) down a telephone line. That鈥檚 65 per
cent more data than many people thought possible with analogue technology. Not
to be outdone, one of its biggest rival, US Robotics, announced that its version
would be ready first鈥攁nd it is starting to appear now. Other
manufacturers, notably Lucent Technologies and Motorola, have also joined the
field. But with data-hungry video and sound growing more popular on the Net,
even 56 kbps is unlikely to keep Internauts happy for long. 鈥淧eople looking for
Internet access . . . are desperately looking for higher-speed solutions,鈥� says
Mike Henderson of Rockwell.
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So the battle for supremacy will not end at 56 kbps. And predicting what will
happen next is made all the harder by the fact that simple copper telephone
wires are no longer the only route by which data can reach many homes. As new
cable TV networks are built and old ones upgraded, more people have the option
of connecting their computers direct to high-capacity coaxial cable. So the data
race has not just engulfed modem makers, its has also pitched phone companies
against cable companies. The result of this competition will have profound
implications for anyone who uses the Net.
In the short term, the modem as we know it is expected to stay ahead of the
game. It will take time for competitors to improve on it for simplicity,
flexibility and cost. And the jump to 56 kbps can only help to consolidate its
position.
Simply put, modems change the digital signals from a computer into a form
that can be sent down an analogue phone line or TV cable鈥攁nd vice versa.
Until now, they have done this by using the digital signal to modulate the
amplitude and phase of a pure sine wave. The receiving modem demodulates the
wave to retrieve the original data.
Using this system, the maximum data rate for an analogue phone line is
irrevocably limited to about 35 kbps. This figure emerges from a theory set out
in the 1940s, which says that the maximum rate is dictated by signal strength,
noise level and bandwidth, which for a phone is just over 3 kilohertz. Only one
of these values is not set in stone鈥攖he noise level. And reducing this has
proved the key to reaching 56 kbps.
Two developments have made this possible, says Martin Rauchwerk of Lucent.
First, most people now tend to use their modems to connect to just one
destination鈥攖heir Internet service provider. Secondly, many of these
service providers now have private digital links to their local telephone
exchanges. Since most telecoms networks these days are almost entirely digital,
these developments mean the only place that data need to be analogue is on the
Net user鈥檚 own information driveway.
Cutting out the toing and froing between analogue and digital on the service
provider鈥檚 side of the telephone network can reduce noise significantly. The
biggest cuts come from doing away with analogue-to-digital converters, which
introduce noise simply because it is impossible to create an exact digital
replica of a continuous, modulated wave. The new systems exploit this
lower-noise regime. Data coming from the Net are encoded by the service provider
into a digital form that passes through the telephone network without generating
extra noise. The Net user鈥檚 local exchange changes the digital pulses into a
stream of discrete analogue voltages, which the user鈥檚 modem converts back into
the original data (see Diagram on p 35). Without the low noise level, the fine
distinction between these voltages would be lost and the modem would be unable
to tell them apart. But so long as noise stays low, data rates of 56 kbps are
possible.
The disadvantage with the new modems is that their upload speeds will be
confined to 33.6 kbps, because there is still an analogue to digital converter
at the phone company鈥檚 end of the information driveway. But for Net surfers this
will not be a problem since most of time they are downloading Web pages. The
signals they send upstream are usually no more than a few keystrokes.
A potentially more serious problem is that the modems do not work to one
standard, and a fierce battle to set a new standard is in full swing. Rockwell,
Lucent and Motorola have reached an agreement, so that modems made with their
chips should be compatible. This has left US Robotics modems out on its own, but
by getting its modem out first the company hopes that its system will become the
standard by default.
The International Telecommunication Union, which sets data transmission
standards, is not expected to rule on this issue before the middle of this year
at the earliest. But at least when the battle is resolved, nobody will be left
with obsolete equipment. The new modems are controlled by software, so they can
be reprogrammed to work to whatever standard the ITU eventually decides on.
The speed of the new modems brings them perilously close to the 64 kbps that
phone companies use for their internal digital networks. So it seems once again
that modems are reaching their absolute limit. Yet Lucent already claims that
its chips can send data digitally to the Net at 40 kbps, and there are hints
that the technology wizards haven鈥檛 given up yet. 鈥淲ill the 56 kbps speeds
become bidirectional? Probably,鈥� says Nicholas Sargologos of Motorola. 鈥淲ill 56
kbps be the very top speed achievable with an analogue type modem? Probably
苍辞迟.鈥�
The new modems will also come close to the long-standing digital option for
telephone subscribers, known as the integrated services digital network. ISDN
channels work at 64 kbps, but they come in pairs that can be hitched together to
give a pipe that can handle 128 kbps. Though ISDN has been around for more than
a decade, it has failed to catch on with domestic users and is only now starting
to become popular among business users. Its chief disadvantages are that it
requires special equipment for both phones and data, and costs more than an
ordinary phone line.
So will the new generation of modems further dent ISDN鈥檚 prospects? Mark
McMillan, senior product manager with US Robotics, is confident that they won鈥檛.
鈥淚n fact, ISDN sales are going to increase because of it.鈥� The reason, he says,
is that many small service providers without a digital link to the phone network
will rush to install ISDN as a cheap way to offer their customers a 56 kbps
service.
Beyond the new modems and ISDN lie the 鈥渂roadband鈥� systems, where data rates
are measured in millions of bits per second (Mbps). This is where cable TV
companies are mounting their challenge to phone companies. They can slip a data
channel into the place normally occupied by a TV channel without disturbing
anyone鈥檚 favourite show. In the US, each TV channel occupies around 6 megahertz
of bandwidth, and in Europe it鈥檚 8 megahertz. Using all this bandwidth would
translate to 30 Mbps in the US and 41 Mbps in Europe, so the potential exists
for astronomical data rates. The reality is less spectacular but still
impressive: existing 鈥渃able modems鈥� work at speeds up to 10 Mbps.
In the customer鈥檚 house, a black box splits the signal between the television
and a cable modem. Just as the television can be tuned into any channel, so the
cable modem is tuned to the data channel. In many cases, the data are sent using
modulation techniques similar to those used in conventional modems. To manage
the data, cable companies often treat their cable systems like local area
networks (LANs), in which a central computer acts as a 鈥渟erver鈥� to the
customers鈥� computers. This allows them to buy standard LAN software and
hardware.
Although at first sight cable networks may look better than phone lines for
sending data, they do not have things all their own way. Especially with older
networks, many customers must share the channel set aside for data, so data
speeds can slow down as more people use the network. Experience with office LANs
suggests that the actual data rate is about one-fifth of the available rate. In
practice, however, sharing should not cause too much of a problem. Computer
traffic is 鈥渂ursty鈥�, observes David Samuel, president of Rogers Wave, a division
of the major Canadian cable company Rogers Cablesystems. 鈥淚f you鈥檙e downloading
a file, you digest it for a couple of minutes,鈥� he says. 鈥淎nd then you download
something else.鈥� This pattern makes sharing bandwidth much less of problem, he
says.
Another potential problem is that when older cable networks were built,
nobody imagined that people using them would be sending signals back to the
operator, so there are no channels in the upstream direction. In fact these
signals are liable to be regarded by the network as noise and cut out by
filters. On these networks, cable modems may be forced to transmit upstream at
low frequencies, below those normally used for television, where the network鈥檚
noise protection system is not active. And unless the cable network is
relatively free of noise, data may have to be sent back in the traditional
way鈥攙ia a modem attached to an ordinary phone line.
Speed wars
These problems are worse in the US and some European countries than in
Britain, where most cable networks have only been laid in the past decade. Most
British systems were designed with a channel for sending data back to the cable
company; they include more optical fibre, which gives very wide bandwidth, and
fewer homes share each part of the bandwidth.
Cable modems are now being installed increasingly in the US. Britain is just
behind says Alan Mitchell, technical director of the London-based Cable
Communications Authority. 鈥淭hey鈥檙e in trials now,鈥� he says. 鈥淚n general, you
can鈥檛 phone up and say `I鈥檇 like a cable modem鈥�.鈥� But the cable network
operators reckon that the modems will become available this year, Mitchell
says.
In the face of this threat the telephone companies have been hard at work on
their own brand of broadband technology, called digital subscriber line or DSL.
Phone companies like it because it can be installed line-by-line as subscribers
request it without having to dig up the road. Better still, it can deliver data
at blazing speeds.
Talk and surf
Copper telephone wires can carry signals with frequencies up to 1.1 megahertz
over several kilometres, yet the plain old telephone service uses only about the
first 4 kilohertz. The remaining bandwidth is empty and available, allowing DSL
to exploit the frequency space above 26 kilohertz. And because the modems used
for DSL tune into just this segment of bandwidth, it is possible to talk on the
phone while transmitting data.
DSL relies on modulation techniques similar to those used in conventional
modems. The bandwidth they exploit can be changed to avoid segments of the
frequency spectrum that are prone to interference. This flexibility can also be
turned to other uses. If a high download capacity is needed, for example, most
of the bandwidth can be earmarked for downstream data, leaving only a narrow
channel for upstream traffic. This is asymmetric DSL or ADSL, which itself
exists in various flavours. Some provide more than 6 Mbps downstream and up to
640 kbps upstream. The actual data rate depends on how far down a line the data
destination is. Longer lines mean lower speeds. In fact if you live much more
than 5 kilometres from the local exchange, you are out of luck because the
signal will not reach that far.
With another variant, rate adaptive DSL, the situation is better. A series of
RADSL modems made by Westell of Aurora, Illinois, vary downstream speeds from
600 kbps to nearly 7 Mbps and upstream speeds from 264 kbps to 1 Mbps. The
speeds change second by second depending on line conditions, which pushes the
maximum distance for sending data close to 7 kilometres.
The disadvantage with ADSL is that it is not a 鈥渄ial up anybody anywhere鈥�
type of service. Connections can only be switched by special arrangement with
the phone company, or with special software and hardware. 鈥淵ou nail up your link
all the way to . . . the service provider,鈥� says Joseph Elchakieh,
vice-president of Westell.
Despite this restriction, ADSL is growing in popularity in the US as a means
to access the Net. In Britain, where BT pioneered ADSL as a way to deliver TV
pictures over phone lines, the technique has yet to catch on as a means for
delivering data. 鈥淲e鈥檙e looking at that now,鈥� says Alec Livingstone of BT. 鈥淲e
see it as a very viable piece of technology.鈥�
So who will win the data race? The answer may depend on when and where you
set the finishing line. According to a study by Jupiter Communications of New
York, in the year 2000 analogue modems will still have 65 per cent of the total
online market. The broadband technology with the most penetration will be cable
modems, with an estimated 8 per cent of American households cruising on cable.
ADSL will trail with only 3 per cent of the total market.
After that, ADSL will take off and overtake cable. One reason for this is the
inability of many older cable networks to handle upstream data, and the expense
of upgrading them. To make matters worse for the cable firms, they are typically
much smaller than telephone companies, with smaller resources. Nor are their
networks as widespread as telephone lines. In the US, 97 per cent of homes are
touched by cable, but elsewhere figures vary widely. In Belgium and the
Netherlands, for example, it is about 90 per cent, in Britain and Germany the
number is between 30 and 40 per cent, while in France it is close to zero.
As in all good races there is an outsider that could confound the market
analysts. For the past 18 months in the US and for just a few months in Europe,
a service run by the giant Hughes corporation has allowed people to download
data from the Net via satellite. With DirecPC, the user sends a request over the
telephone line and receives data back at 400 kbps via a satellite dish.
At present, this service costs more than 拢1000 a connection, making it
too costly for most Net surfers. But DirecPC is just the beginning. The British
broadcaster BSkyB is expected to launch a data link to go alongside its
satellite digital TV service later this year. 鈥淪atellite communications are
going to be a significant part of the global IT network,鈥� says Brian Milnes of
Satellite Digital Systems, which markets DirecPC in Britain. So if you fancy a
bet on who will win the data race, remember to keep one eye on the sky.
