Autocratic governments often limit phone and Internet access in tense times. But the Internet has never faced anything like what happened in Egypt on Friday, when the government of a country with 80 million people and a modernizing economy cut off nearly all access to the network and shut down cellphone service.

The shutdown caused a 90 percent drop in data traffic to and from Egypt, crippling an important communications tool used by antigovernment protesters and their supporters to organize and to spread their message.

Vodafone, a cellphone provider based in London with 28 million subscribers in Egypt, said in a statement on its Web site that “all mobile operators in Egypt have been instructed to suspend services in selected areas.” The company said it was “obliged to comply” with the order.

Egypt, to an unprecedented extent, pulled itself off the grid.

“In a fundamental sense, it’s as if you rewrote the map and they are no longer a country,” said Jim Cowie, the chief technology officer of Renesys, a company based in New Hampshire that tracks Internet traffic.