339Peer-to-peer (P2P) networks are a more recent innovation on the Internet. As
mentioned in Chapter 18, “Quality of Service for Real-Time Internet Commu-
nications,” P2P traffic dominates the Internet traffic at present. “Peer-to-peer
computing could usher in the next generation of the Internet, much as we saw
Mosaic usher in the last era” [1].
NOTEMosaic was the first popular browser that made the Web accessible to
millions of users.The history of P2P applications on the Internet started in 1999 with such
applications as Napster that used a central index server. Other innovations
that came later, such as Kazaa managed to function without any central
servers so as to avoid legal and technical problems. Finally, mixed architec-
tures were developed that combined the advantages of the fully distributed
and decentralized architecture with some server-like functions—so called
“supernodes” in a hybrid P2P mode.
P2P was also adopted for Internet communications. The most famous
hybrid P2P network is at present Skype. Skype is the clear leader on VoIP, IM,
and presence with, as of this writing, close to 80 million users and more than 5
million users online during busy hours.