Probabilistic route discovery for Wireless Mobile Ad Hoc Networks (MANETs)

Mobile wireless ad hoc networks (MANETs) have become of increasing interest in view of their promise to extend connectivity beyond traditional fixed infrastructure networks. In MANETs, the task of routing is distributed among network nodes which act as both end points and routers in a wireless multi-hop network environment. To discover a route to a specific destination node, existing on-demand routing protocols employ a broadcast scheme referred to as simple flooding whereby a route request packet (RREQ) originating from a source node is blindly disseminated to the rest of the network nodes. This can lead to excessive redundant retransmissions, causing high channel contention and packet collisions in the network, a phenomenon called a broadcast storm. To reduce the deleterious impact of flooding RREQ packets, a number of route discovery algorithms have been suggested over the past few years based on, for example, location, zoning or clustering. Most such approaches however involve considerably increased complexity requiring additional hardware or the maintenance of complex state information. This research argues that such requirements can be largely alleviated without sacrificing performance gains through the use of probabilistic broadcast methods, where an intermediate node rebroadcasts RREQ packets based on some suitable forwarding probability rather than in the traditional deterministic manner. Although several probabilistic broadcast algorithms have been suggested for MANETs in the past, most of these have focused on “pure” broadcast scenarios with relatively little investigation of the performance impact on specific applications such as route discovery. As a consequence, there has been so far very little study of the performance of probabilistic route discovery applied to the well-established MANET routing protocols. In an effort to fill this gap, the first part of this thesis evaluates the performance of the routing protocols Ad hoc On demand Distance Vector (AODV) and Dynamic Source Routing (DSR) augmented with probabilistic route discovery, taking into account parameters such as network density, traffic density and nodal mobility. The results reveal encouraging benefits in overall routing control overhead but also show that network operating conditions have a critical impact on the optimality of the forwarding probabilities. In most existing probabilistic broadcast algorithms, including the one used here for preliminary investigations, each forwarding node is allowed to rebroadcast a received packet with a fixed forwarding probability regardless of its relative location with respect to the locations of the source and destination pairs. However, in a route discovery operation, if the location of the destination node is known, the dissemination of the RREQ packets can be directed towards this location. Motivated by this, the second part of the research proposes a probabilistic route discovery approach that aims to reduce further the routing overhead by limiting the dissemination of the RREQ packets towards the anticipated location of the destination. This approach combines elements of the fixed probabilistic and flooding-based route discovery approaches. The results indicate that in a relatively dense network, these combined effects can reduce the routing overhead very significantly when compared with that of the fixed probabilistic route discovery. Typically in a MANET there are regions of varying node density. Under such conditions, fixed probabilistic route discovery can suffer from a degree of inflexibility, since every node is assigned the same forwarding probability regardless of local conditions. Ideally, the forwarding probability should be high for a node located in a sparse region of the network while relatively lower for a node located in a denser region of the network. As a result, it can be helpful to identify and categorise mobile nodes in the various regions of the network and appropriately adjust their forwarding probabilities. To this end the research examines probabilistic route discovery methods that dynamically adjust the forwarding probability at a node, based on local node density, which is estimated using number of neighbours as a parameter. Results from this study return significantly superior performance measures compared with fixed probabilistic variants. Although the probabilistic route discovery methods suggested above can significantly reduce the routing control overhead without degrading the overall network throughput, there remains the problem of how to select efficiently forwarding probabilities that will optimize the performance of a broadcast under any given conditions. In an attempt to address this issue, the final part of this thesis proposes and evaluates the feasibility of a node estimating its own forwarding probability dynamically based on locally collected information. The technique examined involves each node piggybacking a list of its 1-hop neighbours in its transmitted RREQ packets. Based on this list, relay nodes can determine the number of neighbours that have been already covered by a broadcast and thus compute the forwarding probabilities most suited to individual circumstances

A Randomized Error Recovery Algorithm for Reliable Multicast

An efficient error recovery algorithm is essential for reliable multicast in large groups. Tree-based protocols (RMTP, TMTP, LBRRM) group receivers into local regions and select a repair server for performing error recovery in each region. Hence a single server bears the entire responsibility of error recovery for a region. In addition, the deployment of repair servers requires topological information of the underlying multicast tree, which is generally not available at the transport layer. This paper presents RRMP, a randomized reliable multicast protocol which improves the robustness of tree-based protocols by diffusing the responsibility of error recovery among all members in a group. The protocol works well within the existing IP multicast framework and does not require additional support from routers. Both analysis and simulation results show that the performance penalty due to randomization is low and can be tuned according to application requirements

Design and implementation of a QoS-Supportive system for reliable multicast

As the Internet is increasingly being used by business companies to offer and procure services, providers of networked system services are expected to assure customers of specific Quality of Service (QoS) they could offer. This leads to scenarios where users prefer to negotiate required QoS guarantees prior to accepting a service, and service providers assess their ability to provide the customer with the requested QoS on the basis of existing resource availability. A system to be deployed in such scenarios should, in addition to providing the services, (i) monitor resource availability, (ii) be able to assess whether or not requested QoS can be met, and (iii) adapt to QoS perturbations (e.g., node failures) which undermine any assumptions made on continued resource availability. This thesis focuses on building such a QoS-Supportive system for reliably multicasting messages within a group of crash-prone nodes connected by loss-prone networks. System design involves developing a Reliable Multicast protocol and analytically estimating the multicast performance in terms of protocol parameters. It considers two cases regarding message size: small messages that fit into a single packet and large ones that need to be fragmented into multiple packets. Analytical estimations are obtained through stochastic modelling and approximation, and their accuracy is demonstrated using simulations. They allow the affordability of the requested QoS to be numerically assessed for a given set of performance metrics of the underlying network, and also indicate the values to be used for the protocol parameters if the affordable QoS is to be achieved. System implementation takes a modular approach and the major sub-systems built include: the QoS negotiation component, the network monitoring component and the reliable multicast protocol component. Two prototypes have been built. The first one is built as a middleware system in itself to the extent of testing our ideas over a group of geographically distant nodes using PlanetLab. The second prototype is developed as a part of the JGroups Reliable Communication Toolkit and provides, besides an example of scenario directly benefitting of such technology, an example integration of our subsystem into an already-existing system.EThOS - Electronic Theses Online ServiceTAPAS EU-IST-2001-34069 Project : EPSR (Engineering and Physical Sciences Research Council)GBUnited Kingdo

Transport multipoint fiable à très grande échelle : intégration de critères de coût en environnement Internet hybride satellite / terrestre

Le travail effectué aborde la problématique des services de communication multipoints fiables à grande échelle. Dans ce contexte, la possibilité de déployer un tel service au moyen d'un satellite géostationnaire émettant en bande Ka est étudiée. L'emploi de la bande Ka introduit cependant une grande variabilité de la qualité de réception au niveau des utilisateurs finals, rendant nécessaire l'utilisation d'un protocole de transport mettant en oeuvre des mécanismes spécifiques. Selon une fonction de coût définie, la comparaison des solutions basées sur IP Multicast classiquement utilisées montre que l'utilisation d'une approche hybride couplant l'utilisation des réseaux satellites et terrestres est avantageuse. Le principe de la proposition, nommée Hybrid Satellite Terrestrial Reliable Multicast, consiste ainsi à choisir, en fonction de la taille du groupe, le moyen de diffusion le plus rentable - au vu d'une fonction de coût définie. Une description détaillée de la proposition inclut le comportement de la source et des récepteurs, et le format des messages échangés. Bien que le principe de cette approche soit simple, plusieurs points durs sont liés à la conception des mécanismes adéquats. Ces problèmes concernent notamment la gestion de la fiabilité (utilisation de code correcteur d'erreur ou FEC), l'estimation de taille de très grands groupes, et la reprise des erreurs par voie terrestre (utilisation de réseaux de pair-à-pairs). Ces mécanismes sont étudiés de manière unitaire afin de déterminer des configurations satisfaisantes, et pour détecter des problèmes de performances. Ces mécanismes étant définis, la proposition de transport a été globalement modélisée, de manière à obtenir une vérification fonctionnelle du service proposé. Le protocole a été décrit au moyen du profil UML temps réel TURTLE. Les résultats de validation ont été obtenus grâce à la chaîne d'outils TTool-RTL, et à CADP. ABSTRACT : This thesis studies issues related to the proposition of large scale reliable multipoint communication services. In this context, the possibility to use a geostationary satellite, emitting in the Ka band, to deploy such a service is analysed. However, the use of the Ka band introduces a high variability of quality of reception. Thus, the use of a transport protocol, implementing specific mechanisms, is mandatory. According to a cost function, the comparison of classical solutions, based on IP Multicast, show that a hybrid approach which uses the terrestrial and the satellite networks is advantageous. Consequently, a protocol named Hybrid Satellite Terrestrial Reliable Multicast is proposed. Its principle consists of choosing, depending on the group size, the more profitable network (i.e. terrestrial or satellite network) to transmit information. This choice is made according to a predefined cost function. A sharp description of the proposition, including the hosts' behaviours and the message set-up, is depicted. In spite of the simplicity of the approach, several obstacles appear when one tries to design appropriate mechanisms. These issues include reliability (use of forward error correction), large group size estimation, and terrestrial error recovery (use of peer-topeer networks). Those mechanisms are studied separately to determine satisfactory configurations, and to detect performance issues. After the definition of those mechanisms, the proposition is globally modelized in order to start the formal validation of the proposed service. The model is realized using the real-time UML profile TURTLE, and the validation results are obtained thanks to the TTool-RTL toolkit, and to Aldebaran

A Randomized Error Recovery Algorithm for Reliable Multicast

An efficient error recovery algorithm is essential for reliable multicast in large groups. Tree-based protocols (RMTP, TMTP, LBRRM) group receivers into local regions and select a repair server for performing error recovery in each region. Hence a single server bears the entire responsibility of error recovery for a region. In addition, the deployment of repair servers requires topological information of the underlying multicast tree, which is generally not available at the transport layer. This paper presents RRMP, a randomized reliable multicast protocol which improves the robustness of tree-based protocols by diffusing the responsibility of error recovery among all members in a group. The protocol works well within the existing IP multicast framework and does not require additional support from routers. Both analysis and simulation results show that the performance penalty due to randomization is low and can be tuned according to application requirements