Intermittently connected mobile networks are wireless networks where most of the time there does not exist a complete path from the source to the destination. There are many real networks that follow this model, for example, wildlife tracking sensor networks, military networks, vehicular ad hoc networks, etc. In this context, conventional routing schemes fail, because they try to establish complete end-to-end paths, before any data is sent. To deal with such networks researchers have suggested to use flooding-based routing schemes. While flooding-based schemes have a high probability of delivery, they waste a lot of energy and suffer from severe contention which can significantly degrade their performance. Furthermore, proposed efforts to reduce the overhead of flooding-based schemes have often been plagued by large delays. With this in mind, we introduce a new family of routing schemes that “spray ” a few message copies into the network, and then route each copy independently towards the destination. We show that, if carefully designed, spray routing not only performs significantly fewer transmissions per message, but also has lower average delivery delays than existing schemes; furthermore, it is highly scalable and retains good performance under a large range of scenarios. Finally, we use our theoretical framework proposed in our 2004 paper to analyze the performance of spray routing. We also use this theory to show how to choose the number of copies to be sprayed and how to optimally distribute these copies to relays.

Traditionally, ad hoc networks have been viewed as a connected graph over which end-to-end routing paths had to be established. Mobility was considered a necessary evil thatinvalidatespathsandneedstobeovercomeinanintelligent way to allow for seamless communication between nodes. However, it has recently been recognized that mobility can be turned into a useful ally, by making nodes carry data around the network instead of transmitting them. This model of routing departs from the traditional paradigm and requires new theoretical tools to model its performance. A mobility-assisted protocol forwards data only when appropriate relays encounter each other, and thus the time between such encounters, called hitting or meeting time, is of high importance. In this paper, we derive accurate closed form expressions for the expected encounter time between different nodes, under commonly used mobility models. We also propose a mobility model that can successfully capture some important real-world mobility characteristics, often ignored in popular mobility models, and calculate hitting times for this model as well. Finally, we integrate this results with a general theoretical framework that can be used to analyze the performance of mobility-assisted routing schemes. We demonstrate that derivative results concerning the delay of various routing schemes are very accurate, under all the mobility models examined. Hence, this work helps in better understanding the performance of various approaches in different settings, and can facilitate the design of new, improved protocols.

VANETs (vehicular ad hoc networks) are emerging as a new network environment for intelligent transportation systems. Many of the applications built for VANETs will depend on the data push communication model, where information is disseminated to a group of cars. In this paper, we present a formal model of data dissemination in VANETs and study how VANET characteristics, specifically the bidirectional mobility on well defined paths, affects the performance of data dissemination. We study the data push model in the context of TrafficView, a system that we have implemented to disseminate information about the vehicles on the road. Traffic data could be disseminated using the cars moving on the same direction, cars moving in the opposite direction, or cars moving in both directions. Our analysis as well as simulation results show that dissemination using only the cars in the opposite direction increases the data dissemination performance significantly.

Mobile wireless ad hoc and sensor networks can be permanently partitioned in many interesting scenarios. This implies that instantaneous end-to-end routes do not exist. Nevertheless, when nodes are mobile, it is possible to forward messages to their destinations through mobility. In these many interesting settings we observe that spatial node distributions are very heterogeneous and possess concentration points of high node density. The locations of these concentration points and the flow of nodes between them tend to be stable over time. This motivated us to propose a novel mobility model, where nodes move randomly between stable islands of connectivity, where they are likely to encounter other nodes, while connectivity is very limited outside these islands. Our goal is to exploit such a stable topology of concentration points by developing algorithms that allow nodes to collaborate in order to discover this topology and to use it for efficient mobility forwarding. We achieve this without any external signals to nodes, such as geographic positions or fixed beacons; instead, we rely only on the evolution of the set of neighbors of each node. We propose an algorithm for this collaborative graph discovery problem and show that the inferred topology can greatly improve the efficiency of mobility forwarding. Using the proposed mobility model we show through simulations that our approach achieves end-to-end delays comparable to those of epidemic approaches and requires a significantly lower transmission overhead.

Abstract—Vehicular ad hoc networks (VANETs) have recently received considerable attention. To support VANET-based applications, it is important to disseminate data from an information source (data center) to many vehicles on the road. Although disseminating data from a server to a large number of clients has been studied in the database community and the network community, many unique characteristics of the VANET bring out new research challenges. In this paper, we propose a data pouring (DP) and buffering paradigm to address the data dissemination problem in a VANET. In DP, data are periodically broadcast to vehicles on the road. In DP with intersection buffering (DP-IB), data poured from the source are buffered and rebroadcast at the intersections. We provide analytical models to explore the dissemination capacity (DC) of the proposed schemes. The analytical models also provide guidelines on choosing the system parameters to maximize the DC under different delivery ratio requirements. Simulation results show that the proposed DP-IB scheme can significantly improve the data delivery ratio and reduce network traffic. Index Terms—Ad hoc networks, broadcasting, data dissemination, dissemination capacity, vehicular networks. I.

Abstract — In this paper we consider information dissemination in vehicular ad-hoc networks (VANETs) in city scenarios. Information dissemination is an important building block of many proposed VANET applications. These applications need a certain dissemination performance to work satisfactorily. This is critical during the rollout of VANETs, when only few cars participate. After analytical considerations, we focus on simulations using a detailed model of a whole city. We assess the dissemination performance depending on the amount of equipped vehicles on the road. For few equipped vehicles, we show that dissemination speed and coverage will not be sufficient. Therefore, we propose to use specialized, but simple and cheap infrastructure, Stationary Supporting Units (SSUs). If a small number of SSUs is installed in a city and connected via some backbone network, the dissemination performance improves dramatically, especially during the VANET rollout phase. Thus, SSUs allow for a faster and earlier rollout of working, dissemination-based VANET applications. I.

Abstract — In this paper, we present a QoS routing protocol called GVGrid for multi-hop mobile ad hoc networks constructed by vehicles, i.e., vehicular ad hoc networks (VANETs). GVGrid constructs a route on demand from a source (a fixed node or a base station) to vehicles that reside in or drive through a specified geographic region. The goal of GVGrid is to maintain a high quality route, i.e. a robust route for the vehicles ’ movement. Such a route can be used for high quality communication and data transmission between roadsides and vehicles, or between vehicles. The experimental results have shown that GVGrid could provide routes with longer lifetime, compared with an existing routing protocol for VANETs. I.

This article presents a class of routing protocols called RBVT, Road-Based using Vehicular Traffic information

Abstract–Vehicular ad-hoc networks (VANETs) promise to enable many novel applications in transportation systems including accident avoidance, congestion sensing, traffic metering, and general in-car information services. Yet implementing multi-hop vehicular communications is highly challenging due to the highly time-varying nature of vehicles. In addition to node mobility and the impediments of wireless communication, a network comprised of moving vehicles is a dynamic system that can be fragmented into many individual components of disparate connectivity. In this paper we describe and analyze a routing scheme that exploits this dynamic connectivity for the purpose of message propagation of attributed (or labelled) data in a fragmented VANET. Our analysis provides upper and lower bounds on message propagation rate as a function of the traffic density, vehicle speed, and radio range; and sheds light into the role played by each of these network parameters. An important insight from our analysis is that vehicle mobility in the opposite traffic direction can be used to achieve substantial gains in message propagation rates. Our analytical findings are supported by extensive simulations. The simulation results indicate that under certain traffic conditions an increase in vehicle mobility results in an order-of-magnitude increase in message propagation rate.

This paper proposes a Trajectory-Based Data Forwarding (TBD) scheme, tailored for the data forwarding in lighttraffic vehicular ad-hoc networks. State-of-the-art schemes have demonstrated the effectiveness of their data forwarding strategies by exploiting known vehicular traffic statistics (e.g., densities and speeds) in these vehicular networks. These results are encouraging, however, further improvements can be made by taking advantage of the growing popularity of GPSbased navigation systems. This paper presents the first attempt to investigate how to effectively utilize vehicles ’ trajectory information in a privacy-preserving manner. In our design, the trajectory information is combined with the traffic statistics to improve the performance of data forwarding in road networks. Through theoretical analysis and extensive simulation, it is shown that our design outperforms the existing scheme.