An overlay maintenance protocol for overlay routing on top of ad hoc networks

peer reviewedThe protocol described in this paper builds and maintains an overlay topology on top of an ad hoc network. The overlay is intended to be used by a routing application. As flooding is a key component of many route discovery mechanisms in MANETs, we evaluate the delivery percentage, bandwidth consumption and time duration of flooding a message on the overlay. We also consider the overlay path stretch as an indicator for the data transfer transmission time. The protocol does not require any information from the underlay routing protocol, nor cooperation from the nodes that do not belong to the overlay. Each overlay node maintains a set of nearest overlay nodes and exchanges its neighbourhood information with them in order to select useful overlay links. Resilience is afforded by setting a minimum number of overlay neighbours. The performance observed over OLSR are good, for all overlay densities and mobility level studied.EU FP6 AN

The Critical Neighbourhood Range for Asymptotic Overlay Connectivity in Dense Ad Hoc Networks

peer reviewedWe define, for an overlay built on top of an ad hoc network, a simple criterion for neighbourhood: two overlay nodes are neighbours if and only if there exists a path between them of at most R hops, and R is called the (overlay) neighbourhood range. A small R may result in a disconnected overlay, while an unnecessarily large R would generate extra control traffic. We are interested in the minimum R ensuring overlay connectivity, the so-called critical R. We derive a necessary and sufficient condition on R to achieve asymptotic connectivity of the overlay almost surely, i.e. connectivity with probability 1 when the number of overlay nodes tends to infinity, under the hypothesis that the underlying ad hoc network is itself asymptotically almost surely connected. This condition, though asymptotic, sheds some light on the relation linking the critical R to the number of nodes n, the normalized radio transmission range r and the overlay density D (i.e., the proportion of overlay nodes). This condition can be considered as an approximation when the number of nodes is large enough. Since r is considered as a function of n, we are able to study the impact of topology control mechanisms, by showing how the shape of this function impacts the critical R.PAI MOTIO

The Critical Neighbourhood Range for Asymptotic Overlay Connectivity in Ad Hoc Networks

We first motivate the use of ad hoc overlays. In particular, we argue that overlay routing could play a role in the spreading of ad hoc networks. We then define a simple criterion for neighbourhood: two overlay nodes are neighbours if and only if there exists a path between them of at most R hops, and R is called the (overlay) neighbourhood range. A small R may result in a disconnected overlay, while an unnecessarily large R would generate extra control traffic. We are interested in the minimum R ensuring overlay connectivity, the so-called critical R. We study conditions on R to achieve asymptotic connectivity of the overlay almost surely, i.e. connectivity with probability 1 when the number of nodes in the underlying ad hoc network tends to infinity (so-called dense networks) or when the size of the field tends to infinity (socalled sparse networks), under the hypothesis that the underlying ad hoc network is itself asymptotically almost surely connected. For dense networks, we derive a necessary and sufficient condition on R, and for sparse networks we derive distinct necessary and sufficient conditions that are however asymptotically tight. These conditions, though asymptotic, shed some light on the relation linking the critical R to the number of nodes n, the field size the radio transmission range r and the overlay density D (i.e., the proportion of overlay nodes). These conditions can be considered as approximations when the number of nodes (resp. the field) is large enough. Since r is considered as a function of n or l , we are able to study the impact of topology control mechanisms, by showing how the shape of this function impacts the critical R.PAI MOTIO

Performance Study of an Overlay Approach to Active Routing in Ad Hoc Networks

peer reviewedWe motivate the use of the active technology for routing in ad hoc networks. We present an active architecture where passive and active nodes can operate together, avoiding any change in the legacy muti-hop routing protocol they use. We detail a basic reactive protocol which can be used to build any overlay on top of an ad hoc network. We model it as an active application called Re-Active Routing (RAR). RAR provides dynamic routing in dense and sparse active overlays. We investigate its performance in static and dynamic environments and show that it depends substantially on the active range, i.e. on the allowed maximal number of hops between two active nodes. For a well-chosen active range, RAR achieves good performance even if the mobility level is high and the overlay density is as low as 12.5 %.PAI MOTIO

Conception d'un protocole de contrôle de topologie pour les overlays construits sur des réseaux ad hoc

peer reviewedNous présentons un algorithme de création d'une structure overlay efficace pour l'inondation de messages entre un sous-ensemble donné de nœuds ad hoc. Nous exposons les similarités que ce problème présente avec celui du contrôle de topologie et soulignons ses particularités. NBO (Neighbour-Based Overlay topology control protocol), emploie uniquement des informations faciles à obtenir : la distance, exprimée en hops, entre chaque paire de nœuds et leur identifiant. Nous avons estimé la qualité de la structure obtenue sur base de la bande passante consommée par inondation, de la charge des nœuds overlay lors d'une inondation, et du temps nécessaire à la réception d'un message par tous les membres de l'overlay. NBO est plus performant que le meilleur protocole de contrôle de topologie overlay homogène possible.PAI MOTIO

Efficient and Resilient Overlay Topologies over Ad Hoc Networks

peer reviewedWe discuss what kind of overlay topology should be pro-actively built before an overlay routing protocol enters a route search process on top of it. The basic overlay structures we study are the K-Nearest Neighbours overlay topologies, connecting every overlay node to its K nearest peers. We introduce a family of optimizations, based on a pruning rule. As flooding is a key component of many route discovery mechanisms in MANETs, our performance study focusses on the delivery percentage, bandwidth consumption and time duration of flooding on the overlay. We also consider the overlay path stretch and the overlay nodes degree as respective indicators for the data transfer transmission time and overlay resilience. We finally recommend to optimize the K-Nearest Neighbours overlay topologies with the most selective pruning rule and, if necessary, to set a minimal bound on the overlay node degree for improving resilience.EU FP6 AN

Neighbour-Based Overlay Topology Control in Ad Hoc Networks

PAI MOTIO