ternet Protocol. For the interested reader, at the end of the chapter there are additional reading materials for more information about the fascinating history of the Internet. Internet Principles Today the Internet is used for file transfer, email, voice, video, gaming, and many, many other applications. We have become dependent on the Internet starting from, the world economy, via businesses big and small, to the normal people who trust the Internet either to keep them connected to the artery of the economic world, or to keep up relationships with their loved ones. It is surprising how big and important the Internet has become in such a short time. However, the versatility of the Internet is not accidental. The reasons lie in the design of the Internet. In the heart of the design of the Internet and the technology that powers it has certain principles. These principles have ensured that the Internet and the Internet technologies enable the current usage of the Internet, which is way beyond the usage and expectations envisioned by anybody at the dawn of the Internet. Let's look at the main principles: packet switched networking; the end-to-end principle; layered architecture; Postel's robustness principle; and creative anarchy. Packet Switched Networking This first principle is very widely used in modern communication networks. However, traditionally, the voice centric networks, such as the Public Switched Telephony Network Introduction (PSTN), were based on a different technological principle - circuit switched networking. In circuit switched networking connections or calls are switched through the network by reserving a circuit from the caller to the callee. Each connection has its own circuit, and the same resource is reserved for the call regardless how much traffic is transferred through that circuit. For instance, a voice call uses exactly the same resources within the network whether the participants speak or are silent. In contrast, the modern data networks are built based on Packet Switched (PS) network