James Fallows, national correspondent for US publication The Atlantic Monthly, has experienced "The Great Firewall of China" firsthand, an experience people from around the world will share this summer when the Olympics comes to that country. Based in Beijing, Fallows has researched the underlying technology that the Chinese use for Internet censorship, and he explained it in a recent article titled "The Connection Has Been Reset." We e-mailed Fallows questions about how the Chinese government controls Internet content available to its citizens, and here's what he had to say.

You describe four blocking mechanisms that the Chinese government uses to prevent Internet users from viewing content considered harmful. How common is it for Chinese Internet users to experience these sorts of redirections, resets and time-out mechanisms? Can you describe your own Internet surfing experience in China?

If you work from a Chinese Internet cafe - which is still where the vast majority of Chinese Internet activity happens, since so few people have connected computers in their own homes - you experience all of these blocking mechanisms as a matter of course. In some places, like schools, the blocking can be much cruder and indiscriminate. For instance, I have been in several public schools where the "connected" Internet computers were prevented from using any search engine whatsoever. It can be surprisingly hard to get around the 'Net if you can't run any searches! In cafes and in most home connections, all the mechanisms I describe would prevail.

In some hotels and other buildings that cater to Western visitors, the controls may be somewhat relaxed. The authorities don't really care that much about what non-Chinese citizens are able to find. But from my apartments in first Shanghai and now Beijing, I was not able to reach a wide variety of sites - including, often, my own blog at the Atlantic - unless I connected through a VPN. As a matter of course I fire up my VPN at the start of any online session, not just for security but because otherwise I'll be blocked the first time I try a Wikipedia or Technorati link.

Your article says the Chinese Internet control system is constantly changing and that citizens don't know what is off-limits on any given day. Does that make the control system more or less effective in your opinion?

My friend Eamonn Fingleton, says in a new book about China (In the Jaws of the Dragon) that many kinds of government control in China are surprisingly effective precisely because they are so variable and unpredictable in the way they're enforced. Fingleton uses the term "selective enforcement" to describe this process; some Chinese people refer to it by a Chinese saying that boils down to, "One eye open, one eye shut." The idea is that if you're never quite sure when, why and how hard the boom might be lowered on you, you start controlling yourself, rather than being limited strictly by what the government is able to control directly.

When it comes to the Internet, this haziness about just what is and is not permissible has two implications. At a purely technical level, it makes it harder to reverse-engineer the firewall's filters. One day, you can reach all pages at the BBC. The next day they're blocked. If you're trying to game out the system, you're stymied. And at a social level, it makes it hard for people to be sure that they're ever operating in a truly safe zone, since the rules of enforcement might shift tomorrow.

Which is worse: the Chinese government's Internet control system or the censorship systems used by the United Arab Emirates (UAE) or Singapore? Why?

Well, I don't like to use terms like "worse" in this situation. I will say that China's approach is less transparent. According to Andrew Lih, whom I quote in the story, when filters in the UAE or Singapore block a transmission, they tell you that, right in your face. When you can't reach a site from a computer in China, you're never quite sure what's happened. Is the problem with your ISP? With the site itself? Or is the firewall? You never know for sure.