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In transportation, packets beat circuits

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POSTED: August 25, 2007 5:03 a.m.

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 copper wires ran out to the street, where they were bundled with more pairs of copper wires, then finally to a telephone central office. At first manually, then automatically, and finally digitally, a connection was established between your pair of wires and the pair of wires terminating in someone 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 information, then routes each packet independently towards its destination. 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 anyone remembers ISDN, the circuit-switched architecture that sucked up billions of dollars in research and development 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 steamrollered by the Internet. 

Packet switching requires a lot more processing power than circuit switching, both at the edges of the network 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 free. And, with sufficient processing power, packet switching always beats circuit switching - for efficiency, for flexibility, for resiliency, for application diversity, for extendability. 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 transmission hierarchy where I spent 10 years of my life: SONET circuits are multiplexed out of T3 circuits which are multiplexed out of T1 circuits which are multiplexed out of individual 64 kb/s voice channels. With automobiles, on the other hand, every "packet" is dumped into the transportation network to be routed directly to its destination. This requires significant processing power. Luckily, most humans have more than sufficient processing power. (To those applying makeup/on a cell phone/munching breakfast while zooming down Georgia 400 at 80 mph: There are limits to multitasking 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-office and back. It’s home to day care to Starbucks to 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 is chief commercialization officer at Georgia Tech. Reprinted with permission of the author by the Georgia Public Policy Foundation, an independent think tank that proposes practical, market-oriented approaches to public policy to improve the lives of Georgians. Nothing written here is to be construed as necessarily reflecting the views of Georgia Tech or the Georgia Public Policy Foundation, or as an attempt to aid or hinder the passage of any bill before the U.S. Congress or the Georgia Legislature.

 

 

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