I finally had a chance to watch some of the Royal Institution Christmas Lectures by by Microsoft Research Chief Research Scientist Chris Bishop that Steve recommended. Wonderful examples of demonstration and illustration of some quite complex and abstract notions (the best illustration, or should I say ‘portrayal’ of shared secret key encryption that I have ever seen).
One notion popped up in the description of Internet routing was Braess Paradox which showed how the failure in the system can make the system stronger overall. With both a colourful illustration of some road traffic as well as a striking demonstration with a weight suspended by linked bungee chords (minute 25:30 of the webcast which requires ‘buying’ the zero cost webcast, registering, checking out and then watching). In short, Braess Paradox states that in a given network (like a road system or the Internet), the route to take is affected not only by distance but also by congestion.
It is quite understandable that if every driver on the road follows the ‘most favourable’ path for them (without consideration of the impact of their decision on the overall traffic in the area), then there will likely be traffic jams around bottleneck in the most advantageous route. The paradox comes in as traffic can actually be reduced by eliminating roads. One would think that the more road capacity the better, but actually sometimes a road failure can actually increase traffic flow overall and reduce everyone’s journey.
Bishop actually cites a real life example where a tunnel was closed down and traffic actually improved:
“This strange effect can actually happen in real life. In Seoul, in Korea, they closed one of the three tunnels through the city and they actually found traffic flow improved.”
A colourful and curious example of a failure of a rope, road or link making the overall network stronger.