Section: Scientific Foundations
Quality of Service
Since it is difficult to develop as many communication solutions as possible applications, the scientific and technological communities aim towards providing general services allowing to give to each application or user a set of properties nowadays called ``Quality of Service'' (QoS), a terminology lacking a precise definition. This QoS concept takes different forms according to the type of communication service and the aspects which matter for a given application: for performance it comes through specific metrics (delays, jitter, throughput, ...), for dependability it also comes through appropriate metrics: reliability, availability; vulnerability for instance in the case of WAN (Wide Area Network) topologies, etc. Moreover, some aspects of QoS have subjective components: the quality of a video stream or an audio signal, as perceived by the user , is related to some of the previous mentioned parameters (packet loss, delays, ...) but in an extremely complex way, and with a strong subjective component.
QoS is at the heart of our research activities: we look for methods to obtain specific ``levels'' of QoS and for techniques to evaluate the associated metrics. Our ultimate goal is to provide tools (mathematical tools and/or algorithms, under appropriate software ``containers'' or not) allowing users and/or applications to attain some level of QoS, with an optimal use of the resources of the communications system considered. Obtaining a good QoS level is a very general objective. It leads to many different areas, depending on the systems, applications and specific goals being considered. Our team works on several of these areas. We can mention the wide family of routing problems, which in Armor go from graph algorithms to routing techniques specialized to operate in the last mile part of the network under extreme performance constraints, our protocol-oriented activities (header compression techniques, interaction between protocols, for instance between IPv4 and IPv6) or the research works around differentiated services. We are also concerned with specific software engineering techniques, namely with middleware technologies in order to hide as much as possible the problems related to resource sharing, scalability and heterogeneity (for instance, such software systems have been successfully used for stationary distributed systems built over fixed networks but they do not suit mobile settings). We also investigate the impact of network QoS on multimedia payloads to reduce the impact of congestion.
