Every computer attached to the Internet (with the right software) can communicate with any other computer attached to the Internet. We saw in Chapter 1 that every computer sold for the last decade has the horsepower necessary to turn voice into digital data streams. Put those two facts together and you get a revolutionary jump in communications technology: any computer can send and receive voice streams to any other computer across the Internet.
Peer-to-peer just means that two devices connect directly to each other without a server managing the transaction (and that’s ignoring all the routers and other Internet servers handling data traffic). When you physically talk to a person in the same room, it’s peer-to-peer. When you mail that person a letter, the Post Office acts as a server in the middle, so it’s not peer-to-peer. When you call that person on the phone, the telephone company and central office switches get in the middle, so it’s not peer-to-peer.
The most used peer-to-peer connections today are web clients to web servers. When you user your browser to view a web site, the systems connect directly to each other without any server in the middle handling the transaction.
Some type of directory service must be available to help users connect to each other. Every device that can be seen publicly on the Internet has a unique sequence of numbers called an IP (Internet Protocol) address. Multiple types of directory services help decipher a long number (such ...