Extensive research on real-world networks from many different domains like communication networks, social networks, protein-protein interaction networks, neural networks, etc. has revealed that many of these networks are similar in the sense that they share basic properties.
A typical example having all basic properties is the depicted snapshot of the AS-level graph of the Internet. Every node is an autonomous system and links exist if the corresponding ASs have a peering agreement for routing data between their respective sub-networks. The data was obtained from the Stanford Large Network Data Collection.
The depicted network has the so-called small-world property, i.e. it has a small diameter and small average distances. The degree distribution of the nodes follows a power-law, i.e. nodes' degrees are heterogeneous and there are many nodes with small degree and a few nodes with very high degree. (The size of the nodes in the network is depicted proportional to their degree.) Moreover, the network has high clustering, i.e. it has an abundance of small cliques and triangles.
