Here's how the Great Firewall of China works
Just to give a real-world example. (With update below.)
September 9, 2006, is the 30th anniversary of Chairman Mao's death. Just now CNN, on the TV in the other room, was beginning a report on the Legacy of Mao and so on. About twenty seconds into the report...
my wife called me in to see what had happened. The screen was all static, as if a cable had been disconnected. A few minutes later, the picture came back, in time for the international weather. That's how it's done.
Update: And here's how it doesn't work. Just now BBC-TV carried its own Mao retrospective. And, five minutes into the thing (now at panel-discussion phase) it's going on unmolested.
An illustration of random enforcement? Of some perceived difference -- in seriousness, in local audience, in whatever -- between CNN and BBC? I don't know.