The shape of the online universe. This image shows the hierarchical structure of the Internet, based on the connections between individual nodes (such as service providers). Three distinct regions are apparent: an inner core of highly connected nodes, an outer periphery of isolated networks, and a mantle-like mass of peer-connected nodes. The bigger the node, the more connections it has. Those nodes that are closest to the center are connected to more well-connected nodes than are those on the periphery.
The core: At the center of the Internet are about 80 core nodes through which most traffic flows. Remove the core, and 70 percent of the other nodes are still able to function through peer-to-peer connections.
The periphery: At the very edge of the Internet are 5,000 or so isolated nodes that are the most dependent upon the core and become cut off if the core is removed or shut down. Yet those nodes within this periphery are able to stay connected because of their peer-to-peer connections.
