-Today, the Internet has become a key standard. In about 2-3 decades, it has become a cornerstone in all the telecommunication networks. Thus, any system has an interest, at least economically speaking, in being integrated into Internet. Why so? First because more and more networks, almost all of them, can approach Internet, be integrated into it, and are so. So if you wish to interconnect with other networks, either you have to work on the interconnection with a given network, or you can interconnect with Internet and thus access every network interconnected with Internet. Secondly, since Internet is very successful because it is global and widely used, most applications and services are designed to work on the Internet network and not only on one given network technology. So if you want to use these applications, the easiest way to do so is to be integrated into Internet instead of redeveloping your application yourself. So there really is a challenge for satellites. I will mention the three positions satellites could have. I believe you saw this rather quickly during week 2. The first position for satellites is to be an access network. When satellites are an access network, they give a direct access to services for the end user. This is similar to the relay that allows your cell phone to access phone services. The network between this relay and you is the access network. Also, if you consider your box as the end user, the ADSL network, the optical fiber or the cable is the access network. Last example, if you consider your cell phone at home, the relay supplying it will be, for example, the box. The Wi-Fi network between your box and your cell phone becomes a kind of access network. Usually we rather talk about femtocell in this situation. Another option is the backhaul position. It is not directly linked to the user, it is about serving the access network of the user, backhaul or backhauling. For example, it can be a network of users onboard a plane or a boat. In that case, if you supply this network of users, you are backhauling. Another example. If you consider a small village with Wi-Fi spots everywhere, you can supply this large Wi-Fi network with a satellite system. The last position for satellites is to be a backbone. Those are symmetrical links that allow the transit of a lot of very high-speed broadband information in the network. These links are located at the core of the network. Usually we use large optical fiber cables. The satellite backbone is mostly a backup if the cables were to be cut or are undergoing maintenance. You can see here the picture of the first submarine cable between England and Canada. We have seen the three satellite positions. Since you well deserve it, we now need to define interoperability and interconnection. For a satellite system, or any other system, being interoperable means talking with devices from different manufacturers and brands as long as they comply with a certain interface. For example, how an iPhone can talk with a Galaxy. Interconnection is about how two technologies can communicate with each other. For example, if you are placing a 3G call, how can you make sure that this 3G connection works with your interlocutor connected in Wi-Fi. This is interconnection. Of course, all of this is a major challenge if one wishes to be integrated into the Internet or any technology. But we still lack an essential notion to understand this: the protocol.
