The Great Firewall
When you use the Internet, it often feels placeless and virtual, but it’s not. It runs on real wires that cut through real geographical boundaries. There are three main fiber-optic pipelines in China, giant underground cables that provide Internet access for the public and connect China to the rest of the Internet outside its borders. The Chinese government requires the private-sector companies that run these fiber-optic networks to specially configure "router" switches at the edge of the network, where signals cross into foreign countries. These routers — some of which are made by Cisco Systems, an American firm — serve as China’s new censors.
text quoted from CLIVE THOMPSON‘s Google’s China Problem (and China’s Google Problem)