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Routing Your Commute

When you live in a Subway city like NYC every morning is full of routing decisions.

Most lines have three areas in their AS:  Brooklyn, Manhattan and either Queens or The Bronx. Our four autonomous systems.
These four autonomous systems combine hundreds of miles (distance),  stops (hop count) and cars (packets). There are also millions of commuters (is it broadcast or many-to-many multicast?) that need to be transferred from one station (router) to another.

Like every good network, the MTA system have multiple backups and while some trains run on the low-cost 56K local lines, others have T3 segments on the express line.

Lucky me, my train uses the local track and make all stops. If it was a RIP system I would definitely have lost my way as I have more than the allowed 15 hops…

This morning, while riding to work and reading my (endless) OSPF notes, I had a blurry moment when my notes came to life. My F train stopped at Broadway-Lafayette station where two of its express mates have a stop. Whenever I get to this station I look across the platform and check if the express train is there. If I see it, I usually hop over and save myself 6-7 minutes – eternity in morning commute time and priceless in routing terms.

For a reason I can’t explain, maybe because I woke up on time and had enough time, a good sit and interesting OSPF reading, I’ve decided that the express will do without me. I stayed on my train to discover that it is waiting and waiting. Finally another express train stopped and this time I had no doubt  in my mind, I crossed the platform and waited for the doors to close. To my surprise the local train left and we didn’t move for few more minutes.

Eventually the train moved and used the local line (which explained the delays), I was late as usual and left with great admiration to those routing protocols – how are they doing it all day, every day and don’t get tired???

NYC Subway - LED panelAnd while at this subject,
am I the only one thinking the new LED screens on the latest trains is one big routing table?

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  1. February 25, 2010 at 9:54 am

    That’s a great analogy, Rofi. I had a similar thought on the inter-city train system in the US as well as with shipping companies like FedEx. There are certain larger cites that are the hubs, and each hub is connected to the next hub. Each hub also has satellite stations which themselves have connections to smaller cities. I picture that whole thing as either BGP or inter-area OSPF. 🙂

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