Net more robust than we think
The internet can withstand attacks on its infrastructure better than people think, say researchers.
Australian researcher Dr Matthew Roughan, of the University of Adelaide, is part of an international team that reports its findings in today's issue of the Proceedings of the National Academy of Sciences.
"The key underlying principal is distribution," says Roughan.
"You don't put critical resources in one place, you distribute them across the network so if any one bit gets broken, the rest can still keep operating."
It might seem obvious that the internet works like this. But Roughan says some influential experts have suggested that the internet is more centralised than we think.
In recent years, such researchers have modelled what they called the "topology" of the network.
They found that most nodes (computers) are only connected to one other node and a few nodes are connected to almost everything.
"This model tends to look a bit like a hub and spoke network, where you have one node in the middle and it connects everything else together," says Roughan.
Central hubs are a classic target for attack and if the internet was structured this way it would be very vulnerable.
But, says Roughan, who has worked as an engineer with large US internet provider, AT&T, those who actually work with networks generally didn't think the hub and spoke model reflects a true picture of the internet.
And now he says he has data to prove this model is wrong.
An optimised HOTnet
Roughan and colleagues collected data from a high-capacity academic network in North America, called Abilene, to build a different model for the internet.
They found that although there are nodes that were highly interconnected these are not at the centre of the network, so if they are attacked this would not matter to the rest of the internet.
This is why, he says, despite numerous physical injuries including the 2001 terrorist attacks on the World Trade Center, the internet has so far never suffered large-scale collapse
"In fact, I was living something like 40 miles from Manhattan on September 11th and significant parts of the internet located on the island kept running despite this terrible disruption," says Roughan.
"The thing about the internet, and the thing that's been really successful, is that local problems don't get propagated."
Roughan says people who build networks spend a lot of time building features that make the internet infrastructure robust.
One example is the software known as routing protocols that, like big detour signs on highways, redirect computers to alternative routes if there is a problem at any one point on the internet.
Roughan says central hubs require large capacity so it's also cheaper to build a network that distributes the load through several routes.
This new model of the internet has been called a "highly optimised network" or HOTnet.
A child of the atomic age
Roughan says the HOTnet structure is consistent with the intention of those who originally designed the internet in the 1960s.
"The Department of Defence in particular in the US decided they wanted to work out how to build a network that could survive an atomic war," he says.
But the internet is less robust in the face of threats it was not designed to survive, in particular viruses, worms and spam that propagate throughout the network.
Luckily, says Roughan, it's harder to distribute a virus to every computer on the internet than it is to bomb a central node.
And this, he says, means the internet is still more robust than we once thought.