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Routing Redundancy: How Much Is Enough?

Internet connectivity is a good thing. Many of us depend on it for everything from our livelihoods to our entertainment. However, the Internet is very fragile and even the The New York Times is worried about it. But they’re primarily concerned with overloads that can occur when everyone on the planet does the same thing at roughly the same time, such as surfing for news about Michael Jackson. Unfortunately, we will never avoid all such scenarios. Physical systems are designed around average and typical peak loads, not around extremely high loads associated with very unlikely events. Who would pay for that?

And this applies to other complex systems besides the Internet. I was in India during 9/11 and, for two days, I could not make a traditional phone call to the US. Why? Everyone in India knows someone in NYC, and they all picked up the phone at the same time to check in on them. The circuits were so overloaded, I couldn’t even get the friendly “Your call cannot be completed as dialed” message.

No system is ever going to be engineered for insanely high loads. If everyone in your town decides to take a shortcut through your neighborhood to avoid an accident on the highway, you are going to have trouble getting out of your driveway. But rather than give up and wait it out, there is something you can do in advance and at reasonable cost: build a second driveway to a different street on the other side of your house, one that isn’t fed by the same access roads from the highway. My latest blog is about building such redundancy into your Internet connectivity, so you aren’t disconnected by a single failure. And while it’s good that the New York Times and various governments are watching the problem, if your business depends on the Internet, you’re largely on your own to audit and verify that you are buying a sufficient level of redundancy for your budget. A lot of fragility problems could be solved by more informed consumers performing the necessary due diligence.

By Earl Zmijewski, VP and General Manager, Internet Data Services

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problem there is.. Dave Howe  –  Aug 16, 2009 10:42 AM

even if you can buy physically diverse and logically diverse service for your hosting center (and multihoming is common practice for hosting centers) there is still no guarantee that you will get more redundancy. Upstreams often buy transit where it is cheapest, so your two “redundant” providers may well be feeding though the same router at some point, to the same transatlantic or far east provider. and once you leave america, there are very few links to india or china, or europe for that matter (unless you care to tolerate satellite bounce time, which is viable for email or even IM, but not really browsing or voip)

And those points are unfortunately not understood Dan Campbell  –  Aug 16, 2009 1:57 PM

And those points are unfortunately not understood but those that have never designed a network or system before, including pro-network neutrality folks who think bandwidth is infinite and free and that you don’t need to manage the system.  Oversubscriptions applies everywhere, not just technical systems.  Checkout lines in a supermarket, tables in a restaurant, lanes on a highway, seats on an airplane.

The recent MJ surge was not unlike a decade ago when the Starr / Clinton/Lewinsky report was released and websites like CNN crashed.

But on 9/11, as I left my office building in DC and walked home, knowing there was still a plane in the air (that would crash in Pennsylvania), wondering if I should leave the city, I too tried my cell phone to make some calls around and of course I got fast busies.  But back in 2001, mobile phone networks were still, well, pretty BAD (let’s be honest).  We often experienced fast busies, calls not going through, dropped calls, interference, no coverage.  9/11 just made it worse for the day.  But that day I was able to use instant messaging and even email to commuicate while the phones were out of commision for a bit.  The Internet was actually more resilient than TDM networks.

Contention ratio guarantees bandwidth wolfkeeper  –  Aug 19, 2009 2:28 AM

If the network is set up correctly the internet gives you guaranteed bandwidth up to the contention ratio you’ve paid for. That’s often enough for a voice connection.

There’s no guarantee that the thing you’re trying to connect to at the far end can handle your traffic of course, but you can negotiate with it before connecting.

There’s also the point that the web caching and particularly the P2P web caches are your friend, particularly in emergencies; those kinds of systems even out the bandwidth usage.

Basically, the internet should still work in emergencies, but the bandwidth you’ll often get will be less than you’re used to. Unless your ISP has lied when they sold you your service anyway.

All bets are off for unforeseen hardware failures though; if all the fibres get cut, you’re on your own, but that’s rare.

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