During the past decades, the Internet as one of the most important networked systems is growing rapidly. In this paper, the evolution of Internet at the autonomous system (AS) level during the past fourteen years is studied. It is shown that the size of Internet grows linearly and the number of ASes increases by around 238.6 per month, also, the Internet is becoming denser over time. Moreover, following the growth of Internet, the degree distribution of the AS-level Internet changes slightly, whereas the Internet becomes more and more heterogeneous. Compared with the randomized network, the AS-level Internet has higher clustering coefficient and more disassortative mixing-pattern by degree. Through the k-core decomposition method, we observe that the central nodes of the Internet interconnect tightly.
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