This manuscript recollects some of my contributions since my PhD defense. These were achieved while I was a researcher at Inria Sophia Antipolis Méditerranée in the Project-Team Maestro. My research activities focus on the modeling and performance evaluation of networks. In fact, this term encompasses a wide variety of situations. One may consider a particular layer in the protocols stack like the access protocol to the communication channels, or focus on the application layer and study overlay networks or cache networks. As a researcher, I first became interested in controlling the access to the medium in wireless networks. Subsequently, I considered on one hand the power save mode of mobile devices and on the other hand the problem of evolutionary routing in networks with reduced connectivity. After studying the energy savings at mobile terminals, I turned my focus on the energy consumption of base stations in cellular networks and on the use of renewable energy sources for their electrical power supply. This line of research has led to the stochastic modeling of solar radiation in order to better take into account renewable energy sources in the performance evaluation of communications networks. Meanwhile, I developed a second line of research at the application level of communications systems. I was first interested in peer-to-peer storage systems. I then studied hierarchical networks of caches such as that of the Domain Name System (DNS). I have also done research work in the framework of partnership projects with private companies. I contributed to a study on the active management of flows at the core of the network (project with the former Alcatel-Lucent Bell Labs, now Nokia) and to the performance evaluation of urban train control based on wireless communications (project with Alstom Transport).