Generating Random Permutations in the Framework of Parallel Coarse Grained Models

We present three algorithms for generating random permutations in the coarse grained model CGM. For each of the proposed algorithms, we study the number of supersteps, the size of the local memory, the overall communicat- ion cost and we check if it gives a permutation with the uniform distribution or not. The proposed algorithms are intended to be simple and of practical relevance. The difficulty, in this paper, lies in proving that they are the desired properties

Towards a Practical and Fair Rate Allocation for Multihop Wireless Networks based on a Simple Node Model

IEEE 802.11 is often considered as the underlying wireless technology of multihop wireless networks. But the use of 802.11 in such networks raises issues, like efficiency and/or fairness issues. Different kinds of solutions have been proposed to overcome these problems. One approach is to design new MAC protocols that provide alternatives to the IEEE 802.11 MAC protocol. Although these solutions are of some interest, it should probably take some time before new wireless network interface cards based on one of these solutions are developed and released. Another approach is to consider that 802.11 will remain the underlying wireless technology and to design solutions above it. Several solutions based on rate allocation have been proposed so far. The main drawback of the proposed solutions is that they rely on a radio medium sharing model that is difficult to compute in a wireless, distributed and mobile environment. Indeed, very few of these solutions have been derived into a network protocol. In this article, we propose a distributed and dynamic rate allocation solution that is based on a simple sharing model. Due to its simplicity, we can derive a network protocol that can be practically used in multihop wireless networks. This protocol provides a fair bandwidth sharing between end-to-end flows while maintaining an efficient overall throughput in the network. This solution has been implemented in NS2 and evaluated by simulations

SBA : un algorithme simple de backoff pour les réseaux ad hoc

National audienceLes performances d'un réseau ad hoc utilisant 802.11 se dégradent quand la charge du réseau augmente. Cette surcharge du réseau peut provenir de sa densité ou du trafic généré. La perte de performance vient essentiellement du protocole MAC (Medium Access Control) mis en place dans le mode DCF du standard 802.11. On trouve dans la littérature plusieurs solutions au niveau MAC permettant de maintenir les performances telles que l'équité ou l'efficacité mais peu de ces solutions n'abordent le problème de l'équité et de l'efficacité conjointement. Dans cet article nous proposons un algorithme de backoff, SBA (Simple Backoff Algorithm), permettant d'obtenir un bon compromis équité-efficacité quand le réseau est surchargé. De plus, notre algorithme est simple car il ne s'appuie que sur des informations locales. L'analyse et les simulations montrent que SBA permet d'obtenir un meilleur compromis entre équité, efficacité et simplicité comparé à certains protocoles décrits dans la littérature

BRuIT : Bandwidth Reservation under Interferences Influence

This paper deals with the bandwidth reservation problem in ad hoc networks and with the influence that interferences between signals have on this problem. We show that interferences could decrease the applications rates. This can be a real problem for applications that need guarantees. We propose a distributed protocol (called BRuIT) for bandwidth reservation in ad hoc networks that takes into account the existence of interferences from far transmissions. The protocol is analyzed through simulations carried out under NS: we evaluate the signaling overhead required for maintaining the knowledge of existing interferences ; we show that this knowledge reduces delays in case of congestion ; we measure the time for rebuilding broken routes ; and finally we show that this protocol maintains the rate of accepted applications.Cet article traite du problème de réservation de bande passante dans les réseaux ad-hoc et de l’influence des interférences hertziennes sur ce problème. Nous montrons que le phénomène d’interférences peut être à l’origine de pertes de bande passante qui peuvent être problématique pour les applications nécessitant des garanties. nous proposons un protocole distribué de réservation de bande passante pour réseaux ad-hoc appelé BRuIT. Ce protocole prend en compte l’existence d’interférences entre transmissions lointaines. Les performances de BRuIT sont analysées au moyen de simulations sous NS

SBA: A Simple Backoff Algorithm for Wireless Ad Hoc Networks

International audienceThe performance of ad hoc networks based on IEEE 802.11 DCF degrade when congestion increases. The issues concern efficiency and fairness. Many solutions can be found at the MAC layer in the literature, but very few solutions improve fairness and efficiency at the same time. In this paper, we design a new backoff solution, called SBA. SBA uses only local information and two contention window sizes. By simulations, we compare SBA with IEEE 802.11 and several alternatives to 802.11 in ad hoc networks. We show that SBA achieves a good trade-off between fairness, simplicity and efficiency

Estimating Average End-to-End Delays in IEEE 802.11 Multihop Wireless Networks

In this paper, we present a new analytic model for evaluating average end-to-end delay in IEEE 802.11 multihop wireless networks. Our model gives closed expressions for the end-to-end delay in function of arrivals and service time patterns. Each node is modeled as a M/M/1/K queue from which we can derive expressions for service time via queueing theory. By combining this delay evaluation with different admission controls, we design a protocol called DEAN (Delay Estimation in Ad hoc Networks). DEAN is able to provide delay guarantees for QoS applications in function of the application level requirements. Through extensive simulations, we compare performance evaluation of DEAN with other approaches like, for instance, DDA

A Utility-based Framework for Assessing Fairness Schemes in Ad-Hoc Networks

Fairness in multihop ad hoc networks has received considerable attention in the literature. A plethora of protocols have been proposed, which compute the ``optimal'' bit rates of the transmitting mobile nodes over short time-scales so that a certain fairness criterion is met. However, there has been limited research on the impact of the varying short-term allocations of these protocols due to nodes mobility on the user-perceived QoS (and social welfare) for services of long duration. In this paper, we introduce a utility-based framework, based on {\em QoS-aware history-dependent} utility functions. These functions quantify the satisfaction that the users of the MANETs obtain from the way their long-lived service sessions are allocated bandwidth, due to the behavior of the fairness protocols proposed for ad hoc networks. Finally, we demonstrate the framework's usefulness, by performing a comparative assessment of the fairness protocol of our previous work with the standard IEEE 802.11

On The Recovery Performance of Single- and Multipath OLSR in Wireless Multi-Hop Networks

International audienceIn this paper, we study and improve the recovery properties of single and multipath routing strategies when facing network failure situations. In particular, we focus our study on two MANET routing protocols: OLSR and its multipath extension MP-OLSR. In various wireless multi-hop network environments, especially in multiple chain topologies, we define and seek to evaluate the latency introduced by these protocols to find a new path after a link failure. Theoretical estimations and simulation results show that, under dual chain-topologies, this latency can be too long and incompatible with the needs of loss and delay constrained applications. As the source nodes cannot detect link failures immediately because of the delay incurred by the well-known nature of link state protocols in general, and of OLSR Topology Control (TC) messages in particular, these nodes keep sending packets along broken paths. We thus study the inconsistencies between the actual network topology and the nodes' own representation. After analyzing the consequences of this long latency, we seek to alleviate these problems with the introduction of adapted mechanisms. We propose three new different schemes and accordingly extend the original OLSR and MP-OLSR protocols in order to decrease the expected latency and improve the protocol performance. Simulation results show a steep decrease of the latency when using these new schemes in dual chain-topologies. We also discuss these results in terms of packet loss, end-to-end delay and overhead

Dynamic Bandwidth Management in IEEE 802.11-Based Multihop Wireless Networks

International audienceIn this paper, we propose a new protocol named DRBT (Dynamic Regulation of Best Effort Traffic) which supports QoS throughput guarantees and provides a distributed regulation mechanism for Best Effort traffic in multihop wireless networks. By adapting dynamically the rate of Best Effort traffic at the link layer, DRBT increases the acceptance ratio of QoS flows and provides a good use of the remaining resources through the network. Our protocol also provides an accurate method to evaluate the available bandwidth in IEEE 802.11-based ad hoc networks which is able to differentiate QoS applications from Best Effort traffic. Through extensive simulations, we compare the performance of our proposal scheme with some others protocols like QPART for instance

Evaluation d'un protocole de régulation de débit dans les réseaux sans fil multisauts

International audienceLe standard IEEE 802.11 est très souvent considéré comme la technologie sans fil sous-jacente dans les réseaux radio multisauts. Il est maintenant bien connu que l'utilisation de ce standard pose des problèmes d'efficacité et d'équité dans de tels réseaux. Ces problèmes proviennent en partie du protocole MAC de 802.11. Une approche possible est de proposer une alternative à ce protocole MAC afin de limiter ou d'éliminer ces problèmes. Néanmoins, il faudra très probablement attendre un certain temps avant de voir apparaître, sur le marché, des cartes sans fil adaptées aux réseaux multisauts. Une autre approche est de considérer que la technologie sous-jacente restera 802.11 pour un certain temps et que les solutions doivent se situer au-dessus de 802.11. Dans [VAN 08], nous avons proposé un algorithme d'allocation de bande passante distribué et dynamique qui reposait sur un modèle simple de partage du médium radio. Dans cet article, nous transformons cet algorithme en un protocole de régulation de débit pour les réseaux sans fil multisauts. Ce protocole, appelé Profiterole, est distribué, asynchrone, dynamique et nécessite peu d'informations sur le réseau. Puis, nous proposons une évaluation détaillée de Profiterole menée sous le simulateur de réseaux NS2. Enfin, nous le comparons à DiffQ, un nouveau protocole de contrôle de congestion dans les réseaux sans fil multisauts