Mobile Coordinated Substitution Network – RESCUE

Access and metropolitan networks are much more limited in capacity than core networks. While the latter operate in over-provisioning mode, access and metropolitan networks may experience high overload due to evolution of the traffic or failures. In wired networks, some failures (but not all) are handled by rerouting the traffic through a backup network already in place. In developed countries, backup networks are adopted wherever possible (note that this is generally not the case for the links between end users and their local DSLAM). Such a redundant strategy may not be possible in emerging countries because of cost issues. When dedicated backup networks are not available, some operators use their 3G infrastructure to recover some specific failures; although such an alternative helps avoid full network outage, it is a costly solution. Furthermore, availability of 3G coverage is still mainly concentrated in metropolitan zones.

When no backup networks are available, it would be interesting to deploy, for a limited time corresponding to the period of the problem (i.e., failure or traffic overload), a *substitution network* to help the base network keep providing services to users. In the RESCUE project, we will *investigate both the underlying mechanisms and the deployment of a substitution network composed of a fleet of dirigible wireless mobile routers*. Unlike many projects and other scientific works that consider mobility as a drawback, in RESCUE we use the controlled mobility of the substitution network to help the base network reduce contention or to create an alternative network in case of failure.

The advantages of an on-the-fly substitution network are manifold: 1) Reusability and cost reduction. Substitution resources are only used when needed compared to a permanent backup network which may be not used very often. Furthermore, substitution nodes can be redeployed at different parts on the network at different times. 2) Deployability. Substitution network may help some parts of the base network where there is no redundancy. It is important to underline that deploying substitution networks is not orthogonal to having traditional backup networks. Instead, it should be seen as complementary. 3) Adaptability. The topology of the substitution network may be adapted to the context, i.e. to the environment as to the on-going traffic so that an efficient delivery service may be provided.

Note that a fundamental aspect of the project is the *decision* strategy, as deploying a substitution network has some counterpart cost. By decision, we mean the judgment concerning the right time a substitution should be deployed (or undeployed when the system estimates that the substitution network is no further needed). To this end, the RESCUE project addresses both the *theoretical* and the *practical* aspects of the deployment of a substitution network. From a theoretical point of view, we will propose a two-tiered architecture including the base network and the substitution network. This architecture will describe the deployment procedures of the mobile routing devices, the communication stack, the protocols, and the services. The design of this architecture will take into account some constraints such as quality of service and energy consumption (since mobile devices are autonomous), as we want the substitution network to provide more than a best effort service. From a practical point of view, we will provide a proof of concept, the architecture linked to this concept, and the necessary tools (e.g., traffic monitoring, protocols) to validate the concept and mechanisms of on-the-fly substitution networks. At last but not least, we will validate the proposed system both in laboratory testbeds and in a real-usage scenario.