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PLACE YOUR TAILGATE ORDER EARLY!
ON TRANSPORTATION AND TECHNOLOGY
Why are so many mass transit policies doomed
to failure? Because packets beat circuits. Let's
explore an analogy.
In the telecommunications world, the big
story of the last 20 years has been the total and
complete triumph of various packet-switching
architectures over circuit-switching. Put simply,
circuit switching started with Alexander Graham
Bell. Your voice was converted to electrical
signals in your telephone, then a pair of cop
per wires ran out to the street, where they were
bundled with more pairs of copper wires, then fi
nally to a telephone central office. At first manu
ally, then automatically, and finally digitally, a
connection was established between your pair of
wires and the pair of wires terminating in some
one else's telephone, and you could talk to each
other. That was state-
of-the-art for over a
century, from 1876
through the 1980s.
Packet switching
divides a signal (your
voice, Internet data
or video, for example)
into multiple standard
"packets" of informa
tion, then routes each
packet independently
towards its destina
tion. Much of the
technology behind this
was sponsored by the
military, so that signals
could "route around"
damage in a wartime
environment. Every
bit of the Internet is
fundamentally packet-
oriented. Hardly any
one remembers ISDN,
the circuit-switched ar
chitecture that sucked
up billions of dollars in
research and develop
ment and was aimed at
deploying a basic rate
64-kilobits-per-second
circuit to every home
and desktop. Lucent
and Nortel (among
others) finally got it
working—just in time
to be steamrolled by
the Internet.
Packet switching
requires a lot more pro
cessing power than cir
cuit switching, both at
the edges of the net
work and in the core
of the network. That's why Alexander Graham
Bell didn't invent it, and that's why the Arpanet/
Internet was limited to 300-bits-per-second text
for much of its early life.
But, courtesy of Moore's Law, processing
power is now so cheap, it might as well be free.
And, with sufficient processing power, packet
switching always beats circuit switching—for
efficiency, for flexibility, for resiliency, for ap
plication diversity, for extendibility. And for
future-proofing.
Basically, anything circuits can do, packets
can do better. That's the lesson of the last 20
years of telecommunications, and it's why Cisco
is now worth 20 times as much as Nortel, when it
used to be the other way around.
The analogy is obvious: Mass transit systems
are circuits. Automobiles are packets. Packet
switching always beats circuit switching.
Mass transit—heavy rail, light rail, trolleys
and buses—means capital-intensive routes with
minimal flexibility. The train stops at a station,
not in front of your house. Perhaps you switch
to a narrower-bandwidth circuit (in Atlanta, a
MARTA bus) to get closer to your house. Then
you switch to a yet-narrower-bandwidth circuit
(your feet) to get all the way to your house. This
is directly analogous to the digital transmis
sion hierarchy where I spent 10 years of my life:
SONET circuits are multiplexed out of T3 circuits
which are multiplexed out of T1 circiits which
are multiplexed out of individual 64 kilobits-per-
second voice channels.
With automobiles, on the other hand, every
"packet" is dumped into the transportation net
work to be routed directly to its destination. This
requires significant processing power. Luckily,
most humans have more than sufficient process
ing power. (To those applying makeup/ on a cell
phone/ munching breakfast while zooming down
GA 400 at 80 mph: there are limits to multitask
ing for any CPU.) So automobiles take you door
to door. More importantly, they take you door-
to-door-to-door-to-door. Most people's schedules
aren't just home to the office and back. It's home
to day care to Starbucks to the office to a lunch
date to the bank to the office to the dry cleaner
to Little League to home to dance practice to
Applebee's to the mall and home again.
I defy anyone to navigate an itinerary like
that in American suburbia using mass transit.
Packet switching always beats circuit switching.
Stephen Fleming
To be continued...
Stephen Fleming is Chief Commercialization Officer at
Georgia Tech. Reprinted with permission of the author
and the Georgia Public Policy Foundation, an indepen
dent think tank that proposes practical, market-oriented
approaches to public policy to improve the lives of
Georgians. Not to be construed as necessarily reflecting
the views of Georgia Tech or the Georgia Public Policy
Foundation.
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