HINT - from opportunistic network characterization to application development

Delay Tolerant Networks are currently a promising alternative to infrastructure-based networks, but they have not seen a wide deployment so far. There are several ways to evaluate the performance of such networks: field trials, theoretical models, simulation, emulation or replaying contact datasets. Each one has its advantages and drawbacks in terms of material cost, realism, required time or ability to manage real nodes. However, none of them effectively addresses the needs of application developers. In this thesis, we will focus on emulation. In a first part, we will deal with possible inputs for such a system. We first propose an analytical model to predict the drop ratio in a network where nodes have a one-packet buffer. Then, taking inspiration from trace scaling approaches from the literature, we study the hypotheses and assumptions taken for real traces statistical analyses, showing their impact on the obtained probability distributions and observed network performance metrics. We then extend this study to the whole life cycle of real traces, by considering data collection, filtering and scaling. In a second part, we propose a possible architecture for a hybrid DTN emulator, using both real nodes as smartphones and virtual nodes. The main advantage here is to be able to evaluate real applications, including preexisting ones, in a DTN context, doing so as transparently as possible. We identify the limitations of existing approaches, which helps us build a list of specifications for our system. Then, we propose a system called HINT which matches these specifications. HINT is validated, and applied to the study of some examples

Following the Right Path: Using Traces for the Study of DTNs

Contact traces collected in real situations represent a popular material for the study of a Delay Tolerant Network. Three main use cases can be defined for traces: social analysis, performance evaluation and statistical analysis. In this paper, we perform a review on the technicalities of real trace collection and processing. First, we identify several factors which can influence traces during collection, filtering or scaling, and illustrate their impact on the conclusions, based on our experience with four datasets from the literature. We subsequently propose a list of criteria to be verified each time a trace is to be used, along with recommendations on which filters to apply depending on the envisioned use case. The rationale is to provide guidelines for researchers needing to perform trace analysis in their studies

Low Complexity Scalable Iterative Algorithms for IEEE 802.11p Receivers

In this paper, we investigate receivers for Vehicular to Vehicular (V2V) and Vehicular to Infrastructure (V2I) communications. Vehicular channels are characterized by multiple paths and time variations, which introduces challenges in the design of receivers. We propose an algorithm for IEEE 802.11p compliant receivers, based on Orthogonal Frequency Division Multiplexing (OFDM). We employ iterative structures in the receiver as a way to estimate the channel despite variations within a frame. The channel estimator is based on factor graphs, which allow the design of soft iterative receivers while keeping an acceptable computational complexity. Throughout this work, we focus on designing a receiver offering a good complexity performance trade-off. Moreover, we propose a scalable algorithm in order to be able to tune the trade-off depending on the channel conditions. Our algorithm allows reliable communications while offering a considerable decrease in computational complexity. In particular, numerical results show the trade-off between complexity and performance measured in computational time and BER as well as FER achieved by various interpolation lengths used by the estimator which both outperform by decades the standard least square solution. Furthermore our adaptive algorithm shows a considerable improvement in terms of computational time and complexity against state of the art and classical receptors whilst showing acceptable BER and FER performance

A Markov chain model for drop ratio on one-packet buffers DTNs

Most of the efforts to characterize DTN routing are focused on the trade-off between delivery ratio and delay. Buffer occupancy is usually not considered a problem and most of the related work assumes infinite buffers. In the present work, we focus on the drop ratio for message forwarding considering finite buffers. We model message drops with a continuous time Markov chain (CTMC). To the best of our knowledge, there is no previous work with such approach. We focus on the worst case with 1-packet buffers for message forwarding in homogeneous inter-contact times (ICT) and 2-class heterogeneous ICT. Our main contribution is to link the encounter rate(s) with the drop ratio. We show that the modeled drop ratio fits simulation results obtained with synthetic traces for both cases

Demo: Using the HINT Network Emulator to Develop Opportunistic Applications

In this work, we show how to use HINT, a real-time event-driven network emulator, to support the development process of opportunistic applications. In this demo, we use this emulator in conjunction with an example Android chat application to demonstrate its features

HINT: from Network Characterization to Opportunistic Applications

The increasing trend on wireless-connected devices makes opportunistic networking a promising alternative to existing infrastructure-based networks. However, these networks offer no guarantees about connection availability or network topology. The development of opportunistic applications, i.e., applications running over opportunistic networks, is still in early stages. One of the reasons is a lack of tools to support this process. Indeed, many tools have been introduced to study and characterize opportunistic networks but none of them is focused on helping developers to conceive opportunistic applications. In this paper, we argue that the gap between opportunistic applications development and network characterization can be filled with network emulation. As proof of concept, we propose and describe HINT, a realtime event-driven emulator that allows developers to early test their opportunistic applications prior to deployment. We introduce the architecture and corresponding implementation of our proposal, and conduct a preliminary validation by assessing its scalability

Complexity Efficient Decoder Design for Vehicular Communication

Vehicular communication is currently seen as a key technology for enabling safer and more comfortable driving. In the general effort to reduce the number of casualties and improve the traffic flow despite an increasing number of vehicles, this field has a promising future. IEEE 802.11p has been chosen as the standard for the Physical Layer (PHY) design for wireless vehicular communication. However, the channels encountered in such situations pose several challenges for reliable communications. Time and frequency selectivity caused by dispersive environments and high mobility lead to doubly-selective channels. The systems are expected to conduct proper operation, in spite of these disturbances. In this thesis, we focus on the design of receivers working on the PHY layer, with an emphasis on limited complexity. This poses high constraints on the algorithms, which already have to cope with the limited amount of information provided by the training sequences. The solutions considered all involve joint channel estimation and decoding, characterized by the use of an iterative structure. Such structures allow the channel estimation to benefit from the knowledge brought by the decoder, which ultimately decreases the error rate. Following a previous work, we use algorithms based on Minimum Mean Square Error (MMSE) or Maximum A Posteriori (MAP) estimation. These receivers were modified to operate on full frames instead of individual subcarriers, and various improvements were studied. We provide a detailed analysis of the complexity of the proposed designs, along with an evaluation of their decoding performance. The trade-offs between these two parameters are also discussed. A part of these analyses isused in [10]. Finally, we give an insight into some considerations which may arise when implementing the algorithms on testbeds

HINT - de la caractérisation de réseau opportuniste au développement d'applications

Les réseaux tolérants aux délais sont aujourd’hui une alternative prometteuse aux réseaux traditionnels basés sur une infrastructure, encore peu déployée. Il existe plusieurs manières d’évaluer les performances d’un tel réseau : expériences de déploiement grandeur nature, modèles théoriques, simulation, émulation, jeu de traces. Chacune a ses avantages et inconvénients, tant en termes de coûts matériels, de réalisme, de temps nécessaire ou de capacité à gérer des noeuds réels. Cependant, aucune ne répond réellement aux besoins des développeurs d’applications. Dans cette thèse, nous nous focaliserons sur l’émulation. Dans une première partie, nous nous intéresserons aux entrées possibles pour un tel système. Nous proposons tout d’abord un modèle analytique pour prévoir le taux de pertes dans un réseau où les noeuds possèdent une mémoire limitée à un seul paquet. Ensuite, inspirés par les approches de mise à l’échelle de traces de la littérature, nous étudions les hypothèses prises pour l’analyse statistique de traces réelles, et montrons leur influence sur les lois de probabilité obtenues ainsi que les performances réseau observées. Nous étendons ensuite cette étude à la totalité du cycle de vie des traces réelles, en considérant la collecte de données, le filtrage et la mise à l’échelle de celles-ci. Dans une seconde partie, nous proposons une architecture possible d’un émulateur DTN hybride, c’est-à-dire comportant à la fois des noeuds réels sous forme d’intelliphones, et des noeuds virtuels. Le principal avantage ici est de pouvoir évaluer des applications réelles, éventuellement déjà existantes, dans un contexte DTN, et ce de manière aussi transparente que possible. Nous identifions les limites des approches existantes, ce qui nous permet d’établir une liste de spécifications pour notre système. Nous proposons ensuite un système, nommé HINT, permettant de remplir ces spécifications. L’ensemble est ensuite validé, puis appliqué à l’étude de quelques exemples.Delay Tolerant Networks are currently a promising alternative to infrastructure-based networks, but they have not seen a wide deployment so far. There are several ways to evaluate the performance of such networks: field trials, theoretical models, simulation, emulation or replaying contact datasets. Each one has its advantages and drawbacks in terms of material cost, realism, required time or ability to manage real nodes. However, none of them effectively addresses the needs of application developers. In this thesis, we will focus on emulation. In a first part, we will deal with possible inputs for such a system. We first propose an analytical model to predict the drop ratio in a network where nodes have a one-packet buffer. Then, taking inspiration from trace scaling approaches from the literature, we study the hypotheses and assumptions taken for real traces statistical analyses, showing their impact on the obtained probability distributions and observed network performance metrics. We then extend this study to the whole life cycle of real traces, by considering data collection, filtering and scaling. In a second part, we propose a possible architecture for a hybrid DTN emulator, using both real nodes as smartphones and virtual nodes. The main advantage here is to be able to evaluate real applications, including preexisting ones, in a DTN context, doing so as transparently as possible. We identify the limitations of existing approaches, which helps us build a list of specifications for our system. Then, we propose a system called HINT which matches these specifications. HINT is validated, and applied to the study of some examples

Revisiting pitfalls of DTN datasets statistical analysis

International audienceContact traces collected in real situations represent a popular material to assess the performance of a Delay Tolerant Network. These traces usually require some preprocessing to be fully usable. Especially, several assumptions can be made prior to performing the statistical analysis of contact and inter-contact times. We first classify these assumptions, and analyze their impact on the statistical characterization of three well-known datasets. We also identify some pitfalls in dataset analysis that might strongly influence the conclusion made by the experimenter. Based on our own experience, we subsequently propose a preliminary checklist to help researchers avoid undesired ambiguities or misunderstandings in further studies