-But that was before the Internet and the revolution it created throughout all communication forms over the last 10-20 years. Before talking about satellites and their interconnection with the Internet, this part aims at understanding what the Internet is and the important notion that lies behind, the network notion. If you ask anyone in the street what the Internet is in their opinion, if they think about it for a moment, and if this person is not in a technical field, they might answer that Internet is Google, Facebook, YouTube, all the little applications we use on a daily basis, search engines, etc., a lot of services in fact. The very first thing we see, is what the Internet brings us. It is not really the Internet but rather what it gives us access to. It is quite different from the very principle of the Internet. Even if today, these kinds of applications allowed the Internet to become so important in communications. We must start with the network notion. To technically define Internet, we need to see what a network is. Networks do not only exist in the "telecommunications and networks" field. It also exists in water-, power- or fuel-distribution networks. These are also kinds of networks. So what is a network in fact? It is a set of cables, or pipes, and devices interconnected by these cables. In the telecommunication field, these media are cables or wireless and devices can be, for example, your box, phone, routers, switches, but also televisions, etc. The most common thing among all this, the thing that you most commonly see at home, is your own network. On one side there is your box, on the other your television which might operate over Ethernet, and your cell phone which operates over Wi-Fi. This is called a private or local network. It is a type of network. But starting from there, what is the Internet? In fact, the Internet is a set of networks. It is a network made of all the networks in the world that allows us to access anyone connected. At the beginning, it was rather small, 250 users in the 1970s. Over time it got much bigger. Since there were more and more services, all the networks wanted to join the Internet. On this illustration, you can see your own local network connected to a lot of other networks. Today, in 2015, there are just over 3 billion Internet users. In 2009, there were only 1.5 billion users. Today, about half of the world population can access the Internet.