-Hello. We have now reached the last week of this lecture. Together, we will talk about satellite systems, their interconnection and interoperability with other networks, in particular terrestrial networks. But let us first put all this aside. Many notions need to be defined, interoperability, interconnection, where should it be implemented, with which entity. Let us first get back to the satellite communication notion, and more generally, to the communication notion. It might be slightly philosophical, but communication is essential for humanity. Its evolution is linked to communication from the beginning with speech, then writing, the alphabet, and then books, the printing press, etc., until today with the Internet that I am using for this lesson. Human beings have the will to communicate very remotely with as many people as possible, from anywhere to anywhere. For this kind of communication, we always encounter stars as an essential communication medium. Of course, at first we only used stars to receive some information that was not sent by human beings. It could be divinatory interpretations but above all as navigation to find one's bearings. Then, thanks to electromagnetic waves, we managed to send waves towards stars and more precisely towards the Earth's natural satellite, the Moon. This is called Earth-Moon-Earth, EME. Then came along artificial satellites that have strong assets. This is what Laurent called "the strengths of satellites", such as the satellite's coverage, broadcasting, sturdiness, throughput. This is what I illustrated here on several slides so that you can recall these major facts. First, satellites have an important coverage. Geostationary satellites can cover a quarter to a third of the Earth's surface if we do not consider the poles. They can also cover very isolated zones, a small island lost in the middle of the Pacific Ocean, or a plane, a boat in the middle of the ocean, a desert area, anything. No actual terrestrial infrastructure is required. Only energy is required. Finally, they broadcast over this whole coverage. It can be interesting to broadcast to many people simultaneously.