3 - Observations in real-world networks: the Internet, epidemics, proteins and DNA

Summary

During the late 1990s, the advancement and popularity of computers (in particular PCs) changed our understanding of complex networks. The availability and power of computers made it possible to gather huge databases of network structures and to analyze them quickly and efficiently. This allowed, for the first time, the comparison of real network data with the existing models, and, in particular, the ER model. Another significant influence of the computing revolution was the creation of two huge and rapidly developing networks: the Internet and the World Wide Web (WWW).

Real-world complex networks

Below, we present a few examples of real-world networks, many of which are well approximated by a scale-free degree distribution. Many other examples that exist may be found in the recent literature (see e.g. [AB02, BBV08, BLM⁺06, DM03, New02b, PV03]).

Computer networks and the Internet

Computer networks are good candidates for studying the role they play in the Internet. The connections in this case are physical – a link exists between two nodes (computers) in the network if they are physically connected by a cable (usually copper or optical fiber, although some other connection types, such as satellites, exist). Various sizes of networks exist, ranging from a simple LAN (local area network) – where usually a small number of computers are all connected together – to wide area networks (WANs), which may consist of tens of thousands of computers.