In 1989 the Chinese government had enough of the protesters occupying a huge square in the middle of its national capital, so they kicked out the foreign press, shut down communications and rolled in the tanks.
Well, they almost shut down communications…
In 2009 the Iranian government tried the same thing. It didn’t work any better.
Arbor Networks provides a good view on Iran’s connection to the Internet via the Internet Observatory. The fat healthy traffic to the left of the dropoff is what Iranian Internet traffic looks like at normal times, the cliff denotes the election and to the right of that you see traffic increasingly “leaking” past the imposed restrictions.