Farid Benbadis

The Accordion Phenomenon: Analysis, Characterization, and Impact on DTN Routing

We analyze the dynamics of a mobility dataset collected in a pipelined disruption-tolerant network (DTN), a particular class of intermittently-connected wireless networks characterized by a one-dimensional topology. First, we collected and investigated traces of contact times among a thousand participants of a rollerblading tour in Paris. The dataset shows extreme dynamics in the mobility pattern of a large number of nodes. Most strikingly, fluctuations in the motion of the rollerbladers cause a typical accordion phenomenon - the topology expands and shrinks with time, thus influencing connection times and opportunities between participants. Second, we show through an analytical model that the accordion phenomenon, through the variation of the average node degree, has a major impact on the performance of epidemic dissemination. Finally, we test epidemic dissemination and other existing forwarding schemes on our traces, and argue that routing should adapt to the varying, though predictable, nature of the network. To this end, we propose DA-SW (density-aware spray-and-wait), a measurement-oriented variant of the spray-and-wait algorithm that tunes, in a dynamic fashion, the number of a message copies disseminated in the network. We show that DA-SW leads to performance results that are close to the best case (obtained with an oracle).

Density-Aware Routing in Highly Dynamic DTNs: The RollerNet Case

We analyze the dynamics of a mobility data set collected in a pipelined disruption-tolerant network (DTN), a particular class of intermittently-connected wireless networks characterized by a 1-D topology. First, we collected and investigated traces of contact times among thousands of participants of a rollerblading tour in Paris. The data set shows extreme dynamics in the mobility pattern of a large number of nodes. Most strikingly, fluctuations in the motion of the rollerbladers cause a typical accordion phenomenon - the topology expands and shrinks with time, thus influencing connection times and opportunities between participants. Second, we show through an analytical model that the accordion phenomenon, through the variation of the average node degree, has a major impact on the performance of epidemic dissemination. Finally, we test epidemic dissemination and other existing forwarding schemes on our traces, and conclude that routing should adapt to the varying, though predictable, nature of the network. To this end, we propose DA-SW (Density-Aware Spray-and-Wait), a measurement-oriented variant of the spray-and-wait algorithm that tunes, in a dynamic fashion, the number of a message copies to be disseminated in the network. The particularity of DA-SW is that it relies on a set of abaci that represents the three phases of the accordion phenomenon: aggregation, expansion, and stabilization. We show that DA-SW leads to performance results that are close to the best case (obtained with an oracle).

GPS-free-free positioning system for wireless sensor networks

Positioning systems are important components of many communication architectures. The traditional global positioning system (GPS) is impractical in many situations, which makes the need for relative measurement-based approaches. Existing relative solutions lead to good results but generally require that nodes are embedded with specific capabilities. in this paper, we propose GPS-free-free, a simple positioning system based on distances in number of hops between nodes. GPS-free-free make very loose assumptions (only neighborhood discovery) and does not require the computation of complex algorithms. We show through simulations that GPS-free-free leads to good placement results at very low signaling over-head.

Dissecting the routing architecture of self-organizing networks

The proper operation of self-organizing networks (SONs) relies on the autonomous behavior of their individual nodes. Routing in such networks has been a challenging task since their conception, due to their nontraditional characteristics and design requirements. Although a large amount of routing architectures and protocols for SONs has been proposed, very little work has been done on the fundamental characteristics that make a routing strategy efficient for a particular network and/or design requirement. Contrary to traditional techniques where the routing architecture is structured as a single unit, we suggest in this article that routing be thought of as a combination of four main architectural components, namely, addressing, dissemination, discovery, and forwarding. This logical decomposition offers significant advantages from both the analysis and the design perspectives. We conclude from our observations that routing architectures should be scenario-driven, in the sense that the configuration parameters are not necessarily universally good for all application scenarios

Overview and optimization of flooding techniques in OLSR

During this last decade, mesh networks have experienced strong growth due to their ability to provide an additional and complementary support for existing infrastructure communication systems. In such a network, routers are supposed to be fixed for short (e.g. public safety deployment) or long (e.g. network operator extension) period. This relative stability of infrastructure makes proactive routing protocols appropriate. One of the well known proactive routing protocols is OLSR (Optimized Link State Routing), which routing decisions are based on exchanges of topology information using all-to-all flooding of local information in order for each router to build a global knowledge of the topology. This study first goal is to improve the performance of topology information flooding in OLSR by introducing network coding techniques, which leads to a decrease of signaling overhead.

Mobile Data Network Analysis Platform

In this paper we present a platform installed inside a French mobile operators network. This platform is able to capture around 20Gb/s per network probe in the operators Points Of Presence (POPs), capable of extracting useful information at wire speed, and storing it for offline analysis. We detail how efficient network probes can be built using off-the-shelf hardware and software. We describe preliminary experiments which demonstrate that our system can easily extract and process the signaling traffic generated by the connections of a large number of mobile devices (on the order of 50 million signaling messages per hour). This platform is designed to exploit the user traffic as well as the signaling flows and thus to produce performance indicators of Quality of Service (QoS), detecting suspicious traffic or even studying mobility. Moreover, since mobile operators are gradually switching their networks toward full IP, the data mobile network will become the place where everything transits, voice and data.

Tendoc: A Network Coding Video Transmission for Public Safety

This work relies on previous studies that aims at emphasizing the benefit to use Network Coding when one considers a multiple source-destination traffic pattern. This is the case of video transmission between rescue teams on an incident area. The goal of this study is to reduce bandwidth requirements, limited in the case of wireless networks but highly required for the proper functioning of the whole system. In this document, we present the architecture of TenDoc, a software that has been first designed to support any application and that has been adapted especially, here, for the video diffusion case. We also describe a use case scenario to be demonstrated. Keywords-Network coding; Public Safety

Public Safety Situation Aware Services over Cognitive Radio Networks

One of the challenging features of the TVWS for public safety operation is its variation across space and time. More specifically the available channels are not contiguous and vary from one location to another. In addition the white space available in a given location can vary with time if one or more of the TV band primary users start/stop operation. Public Safety Situation Aware services are a main concern when one strives to provide a standard overview of an incident. This standard overview aims at providing intervention information as refreshed as possible to facilitate Incident Commander/Unified Command (e.g. in the case of an European cooperative intervention that involves different Operations Center). Within this study, we propose to investigate how this service can be supported in a Cognitive Radio Network context by considering the unpredictable availability of spectrum resources. We present a Random Network Coding based technique and evaluate the performance assessment of this technique under Cognitive Radio Network assumptions. We show that even for a very restrictive radio resource access, Public Safety Situation Aware services can be fully supported without interfering with a existing primary user activity. Keywords-Common Operational Picture, Public Safety Network, Network Coding

VAPS: Positioning with spatial constraints

The proliferation of mobile computing devices and local wireless networks has promoted a growing interest in location-aware systems. The problem with existing positioning techniques is that they are designed to position dimensionless objects. Such an assumption may lead to practical inconsistencies, as objects might overlap in the resulting coordinate system. Moreover, it is usual to neglect the effects of an object volume and its physical characteristics on signal propagation. In the scenario considered throughout this paper (positioning containers in a harbor), such characteristics can be finely estimated. We propose VAPS, a volume-aware positioning system that takes advantage of the waveguide effect generated by containers. Although VAPS is specific to the harbor scenario, its principles can be extended and adapted to other situations. VAPS maps discrete RSSI levels into hop-counts and relies on realistic propagation models to obtain near-perfect positioning at a very low control overhead. Our results demonstrate that, in scenarios where the assumptions made by traditional approaches fail, the new considerations of VAPS do make a difference.

Demo: opportunistic communications to alleviate cellular infrastructures: the FP7-moto approach

Over the latest few years, we have witnessed the widespread diffusion of smartphones, tablets, and other mobile devices with diverse networking and multimedia capabilities. Major operators in the US and Europe are experiencing severe problems in coping with the mobile data traffic generated by their users. The main reason is that the trend of traffic demand is exponentially increasing, while the improvements at the physical layer are bounded by the famous Shannon theorem and by the fact that the licensed spectrum is a limited and scarce resource. The FP7 MOTO project proposes to design, implement, and evaluate an architecture that takes full advantage of the latest advances in opportunistic networking to achieve effi- cient traffic offloading.