Mobile Ad Hoc Networks: Modelling, Simulation and Broadcast-based Applications. (Réseaux Mobile Ad hoc : modélisation, simulation et applications de diffusion)

Over the last few years, personal communication devices have invaded most developed countries and today, the majority of the population owns a mobile phone and most people use personal digital assistants, mobile computers, etc. This tendency is reinforced and occurs at the same time with a new trend: most of these devices get equipped with one or several wireless networking interfaces. Practically, Wi-Fi or/and Bluetooth-enabled devices become of frequent use. More than allowing the connection to some access point (which can be found in airports, train stations, city-centers, restaurants, etc), these interfaces also permit to interconnect directly with one another in a decentralized way and hence to self-organize into “ad hoc networks”. A mobile ad hoc network is a set of mobile nodes able to communicate with other nodes in their surroundings. These wireless communications happen in a peer-to-peer manner, without relying on any predefined infrastructure. Today, mobile ad hoc networks are mainly used for sensing, gaming and military purposes. But the steadily wider adoption of wireless technologies in daily life let one foresee the next generation of mobile ad hoc network applications: environmental and medical monitoring, groupware, customer-to- customer applications, risk management, entertainment, advertising, etc. In this document we will consider a subclass of mobile ad hoc network called “delay tolerant networks”. In such network, the mobility is hardly predictable and the disruption of connection is a common and normal phenomenon. In order to enable the development and spreading of these applications, a number of issues have to be solved. First, in such networks, end-to-end connectivity cannot be guaranteed. Indeed mobile ad hoc networks may be partitioned and nodes may be spo- radically present in the network. As such, mobile ad hoc networks can be considered as Delay Tolerant Networks (DTN). Second, the topology of the network changes over time because of the mobility of the stations. Then, the way the communication primitives were implemented in the context of wired networks is no longer applicable. It is hence necessary to propose new algorithms to take those primitives into account, like broadcasting that serves as a basic pattern for the design of many mobile ad hoc network applications. The design and implementation of such communication schemes, and more generally of mobile ad hoc network applications, can be achieved using two different ways: either by building a real network, or by resorting to modelling and simulation. Theoretical approaches failed at modeling the inherent complexity of mobile ad hoc networks in a comprehensive manner. Indeed, ad hoc networks are decentralised systems which are ruled by a variety of elements including radio signal, network traffic, mobility, collaborative behavior, etc. If theoretical approaches certainly are useful for represent one or the other elements, they do not suit the modelling of a system as a whole. In the context of this work, where city-scale environment were considered, simulation was hence unavoidable. The development of such simulators took place at the crossroad of some projects in relation to complex system modelling, optimization and middleware design for mobile ad hoc networks, and conducted in several European countries. This diversity led to the design of a custom simulator called Madhoc. Indeed the mobile ad hoc simulators which are already available on the market most often are designed in such a way they allow the simulation of specific applications. They also generally suffer from a complex architecture (often poorly documented) that make them hardly adaptable to other applications. Consequently, none of them apparently turn out to be flexible enough so as it would have met our diverse needs. Madhoc captures the major characteristics of DTNs, by providing an extendable set of mobility models as well as a framework for the definition of new applications. By looking at the State of Art protocols for mobile ad hoc networks and delay tolerant networks, it appeared that the broadcast issue had not yet been solved in a satisfactory manner. Indeed none of the protocols proposed so far proceed nicely in specific conditions of delay tolerant networking. Madhoc was then primarily used for the investigation of the broadcasting issue. In this specific context, networks composed of thousands devices using a variety of wireless technologies were considered. These networks are partitioned and ex- hibit heterogeneous densities. This led to the design of a bandwidth-efficient broadcasting protocol called DFCN.