Packets beat Circuits

So I got in yet another variation of the Mass Transit Discussion over the weekend. I have this discussion often enough that I decided to write up my position here, so that I can just point to it.

First off, you have to know a little history of telecommunications. (I’m a telecom geek, okay?) The big story of the last twenty years has been the total and complete triumph of various packet-switching architectures over circuit-switching.

Very simplistically, 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. State of the art for over a century, from 1876 through the 1980s.

Packet switching divides a signal (could be your voice — VOIP, could be Internet data, could be video, whatever) into multiple standard “packets” of information, then routes each packet independently towards its destination. A lot 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.

Does anyone remember ISDN? I didn’t think so. That was a circuit-switched architecture that sucked up billions of dollars in R&D, aimed at deploying a Basic Rate 64kb/s channel to every home and desktop. Lucent and Nortel (among others) finally got it working just in time to be steamrollered by the Internet. (For a fabulous look at how things fell apart ten years ago, check out Netheads vs. Bellheads at Wired.com. Me? I’m a Bellhead who learned better.)

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 bps 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. For future-proofing. Basically, anything circuits can do, packets can do better. That’s the lesson of the last twenty years of telecommunications, and it’s why Google is worth twice as much as AT&T.

Back to the Mass Transit Discussion:

Mass transit systems are circuits. Automobiles are packets.

Packet switching always beats circuit switching.

Mass transit (heavy rail, light rail, trolleys, busses) means capital-intensive routes with minimal flexibility. The train stops at a station, not in front of your house. Maybe 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 ten 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. (The ones applying makeup while talking on their cellphone while zooming down Highway 400 at 80 mph… well, I wonder about them. 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 drycleaner, to Starbucks, to office, to a lunch date, to the bank, to the office, to Little League, to home, to dance practice, to Applebee’s, to the mall, to home again. I defy anyone to navigate an itinerary like that in American suburbia using mass transit.

Packet switching always beats circuit switching.

“But they do it in New York City,” I hear you cry. Yes, because New York City grew up around mass transit. It’s physically different from Atlanta (or pretty much any other town in America outside the Northeast, except maybe Chicago and San Francisco). The circuits are dense enough to have connection points within walking distance, and the automobile infrastructure is expensive enough to discourage private cars. ($225,000 for a parking space? Bozhe moi!)

Atlanta grew up around cars. It’s fundamentally a packet-switched infrastructure.

Ask any telecom engineer. You cannot replace a packet-switched infrastructure with circuit switching for any reasonable amount of money. Can’t be done.

Look at the cities with successful public transit systems. With the partial exception of the Washington Metro (which violated the “any reasonable amount of money” proviso above), they grew up around rail systems; rail systems were not overlaid after the growth had occurred. (And I’ll note that even the Washington Metro does a lousy job of serving the high-growth suburbs to the west of the city.)

So, as much as I love the plans for the BeltLine, and as much as I enjoy taking the Tube in London, spending public resources on mass transit in Atlanta is a waste of time and money.

But we have real transportation problems in Atlanta. Companies and entrepreneurs are reluctant to move here because of our legendary traffic. Millions of hours are wasted every year by Atlantans sitting in traffic. Cars are spewing megatons of pollution into the air we breathe. We’re the asthma capital of the USA. And all of the money we spend on petroleum is funding both sides of a war where people want to kill us.

Instead of trying to get people out of their cars, why don’t we try solving the real problems caused by cars?

• Time-of-day pricing on toll roads — lots of toll roads! — would help even out the traffic jams. If you really have to be on Highway 400 between 7:30 and 8:30 am, it will cost you two bucks. Between 8:30 and 10:00, it’s a dollar. If you can wait until after 10:00 am, it’s fifty cents.

• Add some lanes to freeways and major arterial routes. Charge for them. Convert HOV lanes to toll lanes. I don’t care if you call them “Lexus Lanes“… they’ll reduce congestion and reduce pollution. (HOV lanes make things worse.)

• Higher gas taxes (and I’m talking an additional dollar or two per gallon) would encourage people to buy smaller more fuel-efficient cars. Not force them… if I really want to drive my 8 mpg sports car, I can do so, I’ll just have to pay more.
• Put more timing lights on the entrance ramps. Build more roundabouts.
• Getting serious about telecommuting a day a week would reduce traffic by 20% right off the bat.
• Zoning changes would encourage more live/work/play complexes like Atlantic Station (hopefully with better security) and Glenwood Park.
• Relaxing the rules against jitneys would allow more people to use the existing mass transit facilities. (Quick, ride MARTA to Cox Communications headquarters! Whoops, the Dunwoody MARTA station is a mile away. Don’t want to walk a mile in Atlanta heat? Sorry, jitneys are illegal here. Pull the car out of the driveway and add another vehicle to the I-285 traffic jam.)
• Charge lots of money ($1000/year or so) for student parking at high schools. They can pay up, or carpool, or take the bus. (Yes, it’s a circuit-switch, but a circuit that’s intentionally routed in front of each student’s door. It’s horribly inefficient, but a high-schooler’s time isn’t worth much.)
• FlexCar and ZipCar are great. If city planners really want to “Do Something,” subsidize more of those.
• Subsidize recharging stations for plug-in hybrids.
• Subsidize cellulosic ethanol refineries.

But for crying out loud, don’t spend billions of dollars on circuit-switched infrastructure that doesn’t address the needs of a packet-switched environment. You could probably do everything on my list above for the cost of a mile of MARTA heavy rail, and it would make a far greater difference in Atlanta’s quality of life.

Packet switching always beats circuit switching.

Those of us in Atlanta (and cities like Atlanta) are going to live in an automobile-dominated world for the rest of our lives. Deal with it, or move back to New York. Let’s make our city work better, rather than wishing for mass transit to do something that is fundamentally impossible.

Tweet