Conception d'un support de communication opportuniste pour les services pervasifs. (Pervasive Service Provisioning in Intermittently Connected Hybrid Networks)

The vision of pervasive computing of building interactive smart spaces in the physical environment is gradually heading from the research domain to reality. Computing capacity is moving beyond personal computers to many day-to-day devices, and these devices become, thanks to multiple interfaces, capable of communicating directly with one another or of connecting to the Internet. In this thesis, we are interested in a kind of pervasive computing environment that forms what we call an Intermittently Connected Hybrid Network (ICHN). An ICHN is a network composed of two parts: a fixed and a mobile part. The fixed part is formed of some fixed infostations (potentially connected together with some fixed infrastructure, typically the Internet). The mobile part, on the other hand, is formed of smartphones carried by nomadic people. While the fixed part is mainly stable, the mobile part is considered challenging and form what is called an Opportunistic Network. Indeed, relying on short-range communication means coupled with the free movements of people and radio interferences lead to frequent disconnections. To perform a network-wide communication, the "store, carry and forward" approach is usually applied. With this approach, a message can be stored temporarily on a device, in order to be forwarded later when circumstances permit. Any device can opportunistically be used as an intermediate relay to facilitate the propagation of a message from one part of the network to another. In this context, the provisioning of pervasive services is particularly challenging, and requires revisiting important components of the provisioning process, such as performing pervasive service discovery and invocation with the presence of connectivity disruptions and absence of both end-to-end paths and access continuity due to user mobility. This thesis addresses the problems of providing networkwide service provisioning in ICHNs and proposes solutions for pervasive service discovery, invocation and access continuity. Concerning service discovery challenge, we propose TAO-DIS, a service discovery protocol that performs an automatic and fast service discovery mechanism. TAO-DIS takes into account the hybrid nature of an ICHN and that the majority of services are provided by infostations. It permits mobile users to discover all the services in the surrounding environment in order to identify and choose the most convenient ones. To allow users to interact with the discovered services, we introduce TAO-INV. TAO-INV is a service invocation protocol specifically designed for ICHNs. It relies on a set of heuristics and mechanisms that ensures performing efficient routing of messages (both service requests and responses) between fixed infostations and mobile clients while preserving both low values of overhead and round trip delays. Since some infostations in the network might be connected, we propose a soft handover mechanism that modifies the invocation process in order to reduce service delivery delays. This handover mechanism takes into consideration the opportunistic nature of the mobile part of the ICHN. We have performed various experiments to evaluate our solutions and compare them with other protocols designed for ad hoc and opportunistic networks. The obtained results tend to prove that our solutions outperform these protocols, namely thanks to the optimizations we have developed for ICHNs. In our opinion, building specialized protocols that benefit from techniques specifically designed for ICHNs is an approach that should be pursued, in complement with research works on general-purpose communication protocols.