What original writing on the topic of networks is yet to be written when thousands of books devoted to the subject have been published? This challenge has been taken up by the authors of this book, who have chosen to highlight the many commonalities of the most significant types of networks in order to identify methods and tools for study. This new approach is thus a welcome addition to the literature.

The concept of network has been in common use for several decades. The word itself is quite old. Its etymology goes back to the Latin retiolus, the diminutive of retis, meaning “net”. The English term network is derived from this same “net”. First used in the domains of textile, medicine and military fortifications, as of the 19th century, the word was used to designate all paths, roads and then railways, which run through a particular region or a country. Information and communication technologies have since become the prominent modern-day meaning.

The structure of this book is broken down into three parts, with corresponding prerequisites set out in the introduction, which responds well to an educational pursuit and to the various expectations of readers: this book is not a novel, and as such does not require a linear reading.

Part 1 presents some of the more significant types of networks that provide services of increasing quality to users in their personal or professional activities. It also describes modeling discrete flow networks, that is, networks in which physical entities or separable and countable information circulate. Modeling is the basis for understanding the phenomena of delays and geographical displacement, which are not necessarily intuitive, and which everyone has been able to observe: why have we been stuck in a traffic jam when subsequently we have observed no accidents or narrowing of the lanes.

Part 2 concerns the methods of performance analysis and evaluation. I have used some of these extensively in my own research on time-constrained communication networks and in the teaching of these same networks. From my own experience, simulation always seems easier than analytical methods. However, while it is unavoidable in complex cases, it sometimes leads to false results if the model is not developed carefully enough – where not all interactions are simulated and where some parameters are poorly estimated.

Part 3 describes three studies on networks whose purposes and operating methods are very different. The case of the social network is particularly instructive. These studies clearly illustrate the gains in service quality provided by certain networks or what non-intuitive results simulations can lead to.

For some time now major issues have emerged, in particular those concerning security and environmental impact that specifically affect networks. While this book only touches upon these issues slightly, it nonetheless allows us to measure their importance by shedding light on the organization and functioning of networks.

I conclude here by congratulating Jean-Paul Bourrières for his idea and for his work in coordinating the writing of this book. I also congratulate all the authors who have contributed to this work through the contribution of their knowledge and the results of concrete studies which infer credibility to the methods and tools presented herein.

Enjoy the book.

Francis LEPAGE

Emeritus Professor

CRAN-UMR 7039 – CNRS

Université de Lorraine

February 2022