The Atlantic's James Fallows has turned in an excellent piece on China's Great Firewall, the censorship system that controls the flow of information into and within China. There's some meaty technical detail here, but the kicker is the social and political impact of the firewall: simply by making it inconvenient to read certain sites, the Chinese government can keep politically charged issues from surfacing in the national discourse:
Thus Chinese authorities can easily do something that would be harder in most developed countries: physically monitor all traffic into or out of the country. They do so by installing at each of these few “international gateways” a device called a “tapper” or “network sniffer,” which can mirror every packet of data going in or out. This involves mirroring in both a figurative and a literal sense. “Mirroring” is the term for normal copying or backup operations, and in this case real though extremely small mirrors are employed. Information travels along fiber-optic cables as little pulses of light, and as these travel through the Chinese gateway routers, numerous tiny mirrors bounce reflections of them to a separate set of “Golden Shield” computers.Here the term’s creepiness is appropriate. As the other routers and servers (short for file servers, which are essentially very large-capacity computers) that make up the Internet do their best to get the packet where it’s supposed to go, China’s own surveillance computers are looking over the same information to see whether it should be stopped...
[I]t would also be wrong to ignore the cumulative effect of topics people are not allowed to discuss. “Whether or not Americans supported George W. Bush, they could not avoid learning about Abu Ghraib,” Rebecca MacÂKinnon says. In China, “the controls mean that whole topics inconvenient for the regime simply don’t exist in public discussion.” Most Chinese people remain wholly unaware of internationally noticed issues like, for instance, the controversy over the Three Gorges Dam.