of Congress Control Number: 2022931615
British Library Cataloguing-in-Publication Data
A CIP record for this book is available from the British Library
ISBN 978-1-78630-657-9
Foreword
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
Introduction
The omnipresence of networks in economic and social organization makes the very concept of networks a paradigm of the contemporary world. The needs for various services (transport, energy, consumption of manufactured goods, healthcare, information and communication, etc.) involve users in an interlinking of networks, which are themselves made up of so many interlinks of both tangible and intangible flows, within which the consumer-citizen is sometimes the recipient of goods and services from industries, and sometimes are themselves a component of the organization (social networks). In this work, the authors questioned the invariants which unify networks in their diversity, as well as the specificities which differentiate them. This book aims to produce, to a certain extent, a unifying vision of networks and the related analysis, modeling and optimization problems, by proposing a reading grid that distinguishes a generic level, where these systems find a common interpretation, and a specific level, where appropriate study methods are mobilized. The presentation of case studies, deliberately drawn from distant fields, aims to exemplify the rationale behind this book through concrete studies.
This book is written in three parts. Part 1, “Network Variety and Modeling”, offers a comparative analysis of the networks that surround us, and presents the general modeling aspects that prevail in an engineering context. The reader will find in Chapter 1 a review of the diversity of networks through a functional approach, that is, by the services provided to the user, with the overarching aim of characterizing and classifying the networks available to us today. We then explore the engineering contexts that arise in connection with networks, as well as the performance issues that accompany them in terms of quality of service, productivity and even environmental impact. Modern engineering is based on models. Before analysis and optimization, the modeling of a system, here a network, uses standardized representation formalisms (IDEF, SADT, GRAI, state machines, Petri networks, queueing networks, UML, etc.), as shared by a smaller number of experts, de facto making each formalism a technical language that facilitates exchanges within a community of specialists. However, this modeling exercise is by no means an objective in itself, nor a method for solving problems, but instead is a simplified representation of a real system, before the engineering logic pertaining to it. In this regard, let us quote the definition given, in the IT field, by OMG (Object Management Group): “A model represents some concrete or abstract thing of interest, with a specific purpose in mind”. Getting into the specifics, the emphasis of Chapter 2 is on the phenomena which govern the flows, whether material or not, that form within a network. We have focused the chapter on the case of discrete flows (of vehicles, material batches, computer data packets, etc.), the kinematics of which turn out to be considerably richer than that of continuous flows (fluid and energy distribution networks). In fact, the separable entities that constitute discrete flows can be the subject of individualized processing and routing within the network, in turn making modeling these flows more complex. We present the main phenomena (resource-flow synchronization, congestion) which determine the kinematics of discrete flows in a network, as well as the diffusion process, which applies more specifically to intangible discrete flows (information and communication networks, digital social networks). Unfortunately, a review of the main discrete flow modeling formalisms shows that none of these formalisms manages, on its own, to cover all of the modeling needs as they emerge from the above, which makes a heterogeneous and multi-scale modeling approach necessary.
