Khaldoun Al Agha

Integration of mobile-IP and OLSR for a universal mobility

Trends in fourth generation (4G) wireless networks are clearly identified by the full-IP concept where all traffic (data, control, voice and video services, etc.) will be transported in IP packets. Many proposals are being made to enhance IP with the functionalities necessary to manage the mobility of nodes, so that networks can provide global seamless roaming between heterogeneous wireless and wired networks. In this paper, we focus on the management of universal mobility, including both large scale macro-mobility and local scale micro-mobility. We propose a hierachical architecture (i) extending micro-mobility management of a wireless access network to an ad-hoc access network, (ii) connecting this ad-hoc network to the Internet and (iii) integrating Mobile IP and OLSR, a routing protocol for ad-hoc networks, to manage universal mobility. This architecture is validated by an implementation based on DynamicsMobile-IP and OLSR version 7. We show how the brodcast of Mobile-IP Agent Advertisement can be optimized using OLSR MPR-flooding.

A shared secret-based algorithm for securing the OLSR routing protocol

The strongest feature of ad hoc networks is its capability to be rapidly deployed anywhere and anytime without relying on a pre-existing infrastructure. From there, ad hoc networks offer the advantages to be auto-organized, ubiquitous, dynamic and completely autonomous. As a counter part, securing them becomes a more difficult task, especially because of the absence of centralized entities in the network. Inevitably, the security problem presents currently a hot topic raising more and more challenges within industrials and researchers, and many interesting securing solutions were meanwhile proposed, omitting however to suit to ad hoc networks characteristics and therefore disadvantaging them. In this paper, we propose a securing scheme for the OLSR routing protocol based on the secret sharing idea. We initially expose the general characteristics and the security problems related to ad hoc routing protocols. We then address the security requirements of ad hoc routing protocols and the security requirements we focus on. Finally, we define our completely and distributed securing algorithm based on threshold cryptography. A primary main conception objective being to suit as much as possible to ad hoc networks characteristics by avoiding as much as possible assumptions contradictory with the auto-organized and dynamic nature of ad hoc networks. Simulation results depict the additional delay due to security enhancements. Results show that this delay stills suitable to OLSR routing specifications.

On Optimality of Myopic Sensing Policy with Imperfect Sensing in Multi-Channel Opportunistic Access

We consider the channel access problem in a multi-channel opportunistic communication system with imperfect channel sensing, where the state of each channel evolves as an independent and identically distributed Markov process. The considered problem can be cast into a restless multi-armed bandit (RMAB) problem that is of fundamental importance in decision theory. It is well-known that the optimal policy of RMAB problem is intractable for its exponential computation complexity. A natural alternative is to consider the easily implementable myopic policy that maximizes the immediate reward but ignores the impact of the current strategy on the future reward. In this paper, we perform an analytical study on the optimality of the myopic policy under imperfect sensing for the considered RMAB problem. Specifically, for a family of generic and practically important utility functions, we establish the closed-form conditions to guarantee the optimality of the myopic policy even under imperfect sensing. Despite our focus on the opportunistic channel access, the obtained results are generic in nature and are widely applicable in a wide range of engineering domains.

Secure and fair auctions over ad hoc networks

The emergence of new mobile and wireless networks, with novel capabilities, offers opportunities to widen traditional internet-based applications. In this paper, we focus on a famous and widely used e-commerce application: auctions, and propose their deployment over ad hoc networks. Actually, we specify here this auction model while assuring identified crucial requirements: security and fairness. Security services are provided through threshold cryptography mechanisms whereas fairness is provided through rounds duration calculation. We prove that such a novel mobile commerce application presents advantages with regard to conventional economic models. Evaluations present optimistic results promising a realisable deployment of our auction model.

On Optimality of Myopic Policy in Opportunistic Spectrum Access: The Case of Sensing Multiple Channels and Accessing One Channel

Recent works have developed a simple and robust myopic sensing policy for multi-channel opportunistic communication systems where a secondary user (SU) can access one of N i.i.d. Markov channels. The optimality of the myopic sensing policy maximizing the SUs expected accumulative reward is established under certain conditions on channel parameters. This paper studies the scenario where the SU, equipped with one radio, can sense k channels but access only one channel each time slot. The objective of the SU is to maximize its throughput over the time horizon T. By characterizing the myopic sensing policy in this context, we establish analytically its optimality for a subset of specific system settings, notably the cases k=2, T=2 and k=N-1 with arbitrary T. In the more generic case, we construct counterexamples to show that the myopic sensing policy is not optimal.

IROCX: Interference-aware routing with opportunistically coded exchanges in wireless mesh networks

Network Coding is a new field that aims at, notably increasing the throughput in a network. ROCX [1] is an algorithm that makes routing with the awareness of network coding. However, its major limitation is that it does not take into account the bandwidth limitation and the interference impact. If the interference is not considered in a wireless network, a flow requiring a certain bandwidth might be accepted and see its throughput decreasing due to interference. In this case, the Quality of Service (QoS) is not respected. Therefore, we use the clique-based model of I2ILP [2] to introduce constraints that consider interference. We present in this paper IROCX, a routing algorithm for wireless mesh networks. It uses Linear Programming for routing while maximizing the benefits of Network Coding and considering interference. The simulation results show the effectiveness of our algorithm.

A Recursive Battery Model for Nodes Lifetime Estimation in Wireless Sensor Networks

Since sensor nodes use batteries as their source of energy, energy-based routing becomes an important requirement to extend network lifetime. This routing is done using the nodes remaining energy information. Nonetheless, this information cannot be estimated using built-in primitives in nodes powered by a lithium-ion battery. In this paper, we introduce an efficient battery model that estimates the remaining energy of a node independently of its battery chemistry. Our model is based on an existing battery model that uses the current consumption during a state and its duration to estimate the battery remaining energy. The original model is very accurate, however, it cannot be implemented in a sensor node as it requires complex computations and large lookup tables. Therefore, we present a recursive approximation of this model that requires low memory and simple computation, while maintaining the original model accuracy. Through extensive real battery discharge measurements, we demonstrate the accuracy of our model and in addition, we show that the ideal model widely used to estimate sensor nodes remaining energy is not accurate.

Admission Control Based on Dynamic Rate Constraints in Multi-Hop Networks

This paper presents an admission control algorithm based on dynamic constraints for multi-hop networks. Assuming each node knows the topology and flow reservations within its radio range, local constraints on flow rates can be computed. As long as these constraints are satisfied, flows are accepted. Since computing optimal constraints is not practical, existing approaches compute a system of either necessary or sufficient constraints. In practice, the approach based on necessary constraints tends to overload the network whereas in the latter approach, a significant part of the bandwidth remains unused. In addition, these works assume that the interference model and the sublayers are optimal. In this paper, we propose to take into account the channel state in the constraints computation and, thus, to adjust them according to model relevance. Therefore we give a probabilistic model to evaluate the time spent by the channel in the idle state. By comparing this estimation with the measure value, we evaluate the model accuracy and include the corresponding error rate in the constraints of the admission control. Simulations show that our admission control algorithm outperforms previous work.

QoS for real-time reliable multicasting in wireless multi-hop networks using a Generation-Based Network Coding

Most of the works on Generation-Based Network Coding (GBNC) consider a fixed generation size. A large generation size maximizes the Network Coding benefits but leads to a long delay while a small generation size reduces the delay but decreases the throughput. This paper presents the DYnamic GEneration Size (DYGES) approach. Our network-aware method adjusts the generation size according to the network variations (network size, congestion, losses) for multicast flows to keep the delay steady. Since Network Coding and redundancy cope with data packet loss, we propose an enhancement of DYGES with ACK recovery. This method, named RDYGES, uses the opportunistic listening feature of nodes to recover the lost ACK. Our goal is to guarantee a Quality of Service (QoS) in terms of delay. The simulation results show the accuracy of our approach.

How to avoid packet droppers with proactive routing protocols for ad hoc networks

Routing protocols for mobile ad hoc networks (MANETs) have been an active area of research for the last decade, with many very interesting potential as well as actual applications, in the military, rescue and commercial fields. Currently emerging standard routing protocols for MANETs do not perform well in the presence of nodes that intentionally drop data traffic but otherwise behave correctly with respect to control messages. In this paper, we address the problem of coping with the presence of such nodes in networks that use a proactive routing protocol. The solution, based on the principle of flow conservation, is purely protocolar and does not rely on any specific underlying OSI layer 1 or 2 technology. In addition, it is well suited for integration into existing proactive routing protocols for ad hoc networks, since it can use existing control messages and does not require any synchronization between the nodes. The method, once implemented in an actual routing protocol, proves to increase the ratio of successfully delivered data packets significantly.