A Framework for Modeling Spatial Node Density in Waypoint-Based Mobility

International audienceUser mobility is of critical importance when designing mobile networks. In particular, "waypoint" mobility has been widely used as a simple way to describe how humans move. This paper introduces the first modeling framework to model waypoint-based mobility. The proposed framework is simple, yet general enough to model any waypoint-based mobility regimes. It employs first order ordinary differential equations to model the spatial density of participating nodes as a function of (1) the probability of moving between two locations within the geographic region under consideration, and (2) the rate at which nodes leave their current location. We validate our models against real user mobility recorded in GPS traces collected in three different scenarios. Moreover, we show that our modeling framework can be used to analyze the steady-state behavior of spatial node density resulting from a number of synthetic waypoint-based mobility regimes, including the widely used Random Waypoint (RWP) model. Another contribution of the proposed framework is to show that using the well-known preferential attachment principle to model human mobility exhibits behavior similar to random mobility, where the original spatial node density distribution is not preserved. Finally, as an example application of our framework, we discuss using it to generate steady-state node density distributions to prime mobile network simulations

Snapshot of MAC, PHY and Propagation Models for IEEE 802.11 in Open-Source Network Simulators

Simulation is an essential component of the validation chain in the design of network protocols. Indeed, while simulation is not the only tool used for data networking research, it is extremely useful because it often allows research questions and prototypes to be explored at many orders-of-magnitude less cost and time than that required to experiment with real implementations and networks. In this report, we focus on the simulation of IEEE 802.11 Physical (PHY) and Medium Access Control (MAC) layers and provide a survey of current IEEE 802.11 network simulators. We believe that such survey will help network researchers to select the best simulator according to the requirements of their simulations. Furthermore, we present a detailed description of the YANS prototype network simulator, and especially its physical layer imple-mentation, which will be partly ported in the upcoming NS-3 network simulator

Utility-based Message Replication for Intermittently Connected Heterogeneous Networks

Communication networks (wired or wireless) have traditionally been assumed to be connected at least most of the time. However, emerging applications such as emergency response, special operations, smart environments, VANETs, etc. coupled with node heterogeneity and volatile links (e.g. due to wireless propagation phenomena and node mobility) will likely change the typical conditions under which networks operate. In fact, in such scenarios, networks may be mostly disconnected, i.e., most of the time, end-to-end paths connecting every node pair do not exist. To cope with frequent, long-lived disconnections, {\em opportunistic routing} techniques have been proposed in which, at every hop, a node decides whether it should either forward and/or store-and-carry a message. As a result, a number of message replicas may be created and routed independently (``spraying''). Most opportunistic routing schemes to-date perform {\em greedy} replication handing over a copy of a message to the first nodes encountered. Yet, in a network with heterogeneous nodes, where some nodes may be much ``better'' relays than others, such greedy schemes waste a lot of message replicas (and thus energy, storage space, etc.) on ``useless'' relays. For this reason, we propose the idea of \emph{utility-based replication}, where some \emph{fitness} or \emph{utility} function is maintained for all nodes in a distributed fashion, and a small budget of message replicas is allocated according to this utility only to the fittest nodes. We describe a number of variations using different utility functions, and show that an improvement of up to 5-6 times in delay can be achieved over greedy algorithms

Adaptive Deployment for Pervasive Data Gathering in Connectivity-Challenged Environments

International audienceSome current and future pervasive data driven applications must operate in "extreme" environments where end-to-end connectivity cannot be guaranteed at all times. In fact, it is likely that in these environments partitions are, rather than exceptions, part of the normal network operation. In this paper, we introduce cover, a suite of adaptive strategies to control the trajectory of "infrastructure" nodes, which are deployed to bridge network partitions and thus play a critical role in data delivery. In particular, we focus on applications where end (or target) nodes are mobile and their mobility is unknown. Our goal is then to deploy and manage infrastructure nodes so that application-level requirements such as reliable data delivery and latency are met while still limiting deployment cost and balancing the load among infrastructure nodes. Cover achieves these goals using a localized and adaptive approach to infrastructure management based on the observed mobility of target nodes. To this end, Cover takes advantage of contact opportunities between infrastructure nodes to exchange information about their covered zones, and thus, help monitor targets in a more efficient fashion. Through extensive simulations, we show how Cover's adaptive features yield a fair distribution of targets per infrastructure node based only on limited network knowledge

MeDeHa - Efficient Message Delivery in Heterogeneous Networks with Intermittent Connectivity

In this report, we present an efficient message delivery mechanism that enables distribution/dissemination of messages in an internet connecting heterogeneous networks and prone to disruptions in connectivity. We call our protocol MeDeHa (pronounced ``medea'') for Message Delivery in Heterogeneous, Disruption-prone Networks. MeDeHa is complementary to the IRTF's Bundle Architecture: while the Bundle Architecture provides storage above the transport layer in order to enable interoperability among networks that support different types of transport protocols, MeDeHa is able to store data at any layer of the network stack, addressing heterogeneity even at lower layers (e.g., when intermediate nodes do not support higher-layer protocols). MeDeHa also takes advantage of network heterogeneity (e.g., nodes supporting more than one network and nodes having diverse resources) to improve message delivery. For example, in the case of IEEE 802.11 networks, participating nodes may use both infrastructure- and ad hoc modes to deliver data to otherwise unavailable destinations. Another important feature of MeDeHa is that it does not rely on special-purpose nodes such as message ferries, data mules, or throwboxes in order to relay data to intended destinations, and/or to connect to the backbone network wherever infrastructure is available. The network is able to store data destined to temporarily unavailable nodes for some time depending upon current storage availability as well as quality-of-service needs (e.g., delivery delay bounds) imposed by the application. We showcase MeDeHa's ability to operate in environments consisting of a diverse set of interconnected networks and evaluate its performance via extensive simulations using a variety of synthetic-- as well as more realistic scenarios. Our results show significant improvement in average delivery ratio and significant decrease in average delivery delay in the face of episodic connectivity. We also demonstrate MeDeHa's support for different levels of quality-of-service through traffic differentiation and message prioritization

Coping with Episodic Connectivity in Heterogeneous Networks

International audienceIn this paper, we present an efficient message delivery mechanism that enables distribution/dissemination of messages in an internet connecting heterogeneous networks and prone to disruptions in connectivity. We call our protocol MeDeHa (pronounced “medea”) for Message Delivery in Heterogeneous, Disruptionprone Networks. MeDeHa is complementary to the IRTF's Bundle Architecture: while the Bundle Architecture provides storage above the transport layer in order to enable interoperability among networks that support different types of transport layers, MeDeHa stores data at the link layer addressing heterogeneity at lower layers (e.g., when intermediate nodes do not support higher-layer protocols). MeDeHa also takes advantage of network heterogeneity (e.g., nodes supporting more than one network) to improve message delivery. For example, in the case of IEEE 802.11 networks, participating nodes may use both infrastructure- and ad hoc modes to deliver data to otherwise unavailable destinations. Another important feature of MeDeHa is that there is no need to deploy special-purpose nodes such as message ferries, data mules, or throwboxes in order to relay data to intended destinations, or to connect to the backbone network wherever infrastructure is available. The network is able to store data destined to temporarily unavailable nodes for some time depending upon existing storage as well as quality-of-service issues such as delivery delay bounds imposed by the application. We evaluate MeDeHa via simulations using indoor scenarios (e.g. convention centers, exposition halls, museums etc.) and show significant improvement in delivery ratio in the face of episodic connectivity. We also showcase MeDeHa's support for different levels of quality-of-service through traffic differentiation and message prioritization

Dynamically Distributed Network Control for Message Dissemination in ITS

International audienceWe propose D2-ITS, a flexible and extensible framework to dynamically distribute network control to enable message dissemination in Intelligent Transport Systems (ITS). By decoupling the control- from the data plane, D2-ITS leverages network programmability to address ITS scalability, delay intolerance and decentralization. It uses a distributed control plane based on a hierarchy of controllers that can dynamically adjust to environment and network conditions in order to satisfy ITS application requirements. We demonstrate the benefits of D2-ITS through a proof-of-concept prototype using the ns-3 simulation platform. Results indicate lower message delivery latency with minimal additional overhead