The Internet, a global system of interconnected networks, has already become a de-facto utility serving billions of people worldwide. Individuals, companies, educational institutions and government agencies use the Internet for communication, entertainment, marketing, administration, collaboration and citizen participation. On the other hand, the Internet is a highly engineered, globally scaled, complex system formed by tens of thousands of autonomous networks operating independently. In this study, we first present a taxonomy of autonomous systems (ASes) which is definite and compatible with the current AS-level structure of the Internet. Then, we analyze different classes of ASes to shed light on the complex structure of the Internet. We believe that our approach and findings will help telecom practitioners gain more insight into the structural and operational characteristics of the Internet and enhance their network infrastructures.