A Survey of Abnormal Traffic Information Detection and Transmission Mechanisms in VSNs <s> Routing-Based Multihop Transmission. <s> The intelligent transportation systems ITS cause a significant passion since the appearance of new inter-vehicles communication mechanisms based on mobile networks. The wireless ad hoc networks, completely distributed and not depending on infrastructures, allow the fast and cheap development of such mechanisms. This article concerns multicast in wireless ad-hoc networks applied to ITS. We propose a new protocol called IVG inter-vehicles geocast which consists in informing all the vehicles of a highway about any danger such as an accident or any other obstacle. In this case, risk areas are determined according to the driving direction and the positioning of the vehicles. These vehicles define a restricted broadcast group, so-called, multicast group. Multicast group, contrary to the classical methods, which use node identities, is defined temporally and dynamically by the location, speed and driving direction of vehicles. Some simulations thanks to Glomosim tool, for which we have defined a model for the road transport, and studies of the complexity are given. The results show that IVG is an efficient broadcast method for secure highway transportation and reduces the number of useful messages. <s> BIB001 </s> A Survey of Abnormal Traffic Information Detection and Transmission Mechanisms in VSNs <s> Routing-Based Multihop Transmission. <s> Geocast in vehicular ad hoc networks allows to realize applications like virtual warning signs for improved road safety, which address a geographical area rather than an individual vehicle. In this paper we propose to include caching in the geocast forwarding scheme and improved neighborhood selection to address in particular the high velocities of vehicles. High velocities of vehicular networks are a major difference to usual mobile ad hoc networks which assume only moderate node movement. We show that a cache for presently unforwardable messages caused by network partitioning or unfavorable neighbors can significantly improve the geocast delivery success ratio. The improved neighborhood selection taking frequent neighborhood changes into account significantly decreases network load and decreased end-to-end delivery delay. <s> BIB002 </s> A Survey of Abnormal Traffic Information Detection and Transmission Mechanisms in VSNs <s> Routing-Based Multihop Transmission. <s> In this paper, we study the effect of dense vehicular networks on data dissemination. When using intelligent broadcast- ing techniques, such as Inter-Vehicle Geocast, we have discovered the spatial broadcast storm problem in which multiple vehicles will be chosen to re-broadcast frames at nearly the same time, resulting in channel contention and collisions. We present a probabilistic version of IVG (p-IVG) to address this problem. In p-IVG, which vehicles re-broadcast frames is probabilistic depending upon the traffic density surrounding the vehicles. We show that p-IVG solves the spatial broadcast storm problem and that using p-IVG results in improved reception rates, lower channel contention, and most importantly, faster dissemination of data to distant vehicles than IVG. I. INTRODUCTION <s> BIB003 </s> A Survey of Abnormal Traffic Information Detection and Transmission Mechanisms in VSNs <s> Routing-Based Multihop Transmission. <s> In order to achieve cooperative driving in vehicular ad hoc networks (VANET), broadcast transmission is usually used for disseminating safety-related information among vehicles. Nevertheless, broadcast over multihop wireless networks poses many challenges due to link unreliability, hidden terminal, message redundancy, and broadcast storm, etc., which greatly degrade the network performance. In this paper, we propose a cross layer broadcast protocol (CLBP) for multihop emergency message dissemination in inter-vehicle communication systems. We first design a novel composite relaying metric for relaying node selection, by jointly considering the geographical locations, physical layer channel conditions, moving velocities of vehicles. Based on the designed metric, we then propose a distributed relay selection scheme to guarantee that a unique relay is selected to reliably forward the emergency message in the desired propagation direction. We further apply IEEE802.11e EDCA MAC to guarantee QoS performance of safety related services. Finally, NS-2 simulation results are given to demonstrate that CLBP cannot only minimize the broadcast message redundancy, but also quickly and reliably disseminate emergency messages in a VANET. <s> BIB004 </s> A Survey of Abnormal Traffic Information Detection and Transmission Mechanisms in VSNs <s> Routing-Based Multihop Transmission. <s> As the rapid progress in vehicular communication technology, academic and industry pay more and more attention to vehicular ad hoc networks (VANETs). In VANETs, the dissemination delay and reliability are important criteria for many applications, especially emergency message dissemination. Existing approaches are hard to satisfy both requirements simultaneously due to the conflict between dissemination delay and reliability. In this paper, we propose a novel mechanism, named Fast and Reliable Emergency message Dissemination Mechanism (FR-EDM) to disseminate emergency message in VANETs. FR-EDM resolves the broadcast storm problem, achieves low dissemination delay, and provides the high reliability in freeway scenario. FR-EDM deliveries the emergency messages as soon as possible to the specific area (e.g., the area before the gateway) and guarantees all relevant vehicles receive the emergency messages in this area such that people can change their routes to destination in time. Consequently, people can avoid getting into a traffic jam. We use ns-2 simulations to evaluate our mathematical model for optimal block size and compare FR-EDM with other protocols. The simulation results show that FR-EDM achieves both lower dissemination delay and higher reliability than existing approaches. <s> BIB005 </s> A Survey of Abnormal Traffic Information Detection and Transmission Mechanisms in VSNs <s> Routing-Based Multihop Transmission. <s> With the extension of wireless technology, vehicular ad hoc networks (VANETs) provide general data transmission services and emergency warning services. To rescue more drivers from being involved in an emergency event on the road, fast emergency message propagation is an important issue in VANET studies. There are two types of multi-hop broadcasting forwarder selection schemes for emergency broadcasting, known as sender-oriented schemes and receiver-oriented schemes. The sender-oriented schemes periodically maintain neighbor information in order to choose the best forwarder before broadcasting the message, while the receiver-oriented schemes distributed elect the forwarders. In this paper, we propose a vehicle-density-based emergency broadcast (VDEB) scheme to solve the problem of high overhead in sender-oriented schemes, and long delay in receiver-oriented schemes. The simulation results show that our VDEB scheme can achieve better performance with low delay and little overhead. <s> BIB006 </s> A Survey of Abnormal Traffic Information Detection and Transmission Mechanisms in VSNs <s> Routing-Based Multihop Transmission. <s> A key design issue in routing for wireless ad hoc networks is scalability. By scalability we mean the ability of the network to support increases in node numbers without significantly degrading network performance. In this work we introduce a new hybrid wireless routing protocol specifically designed to address this issue. Our new protocol combines features of reactive routing with location-based geographic routing, in such a manner so as to efficiently use all the location information available. The protocol is designed to gracefully exit to reactive routing as the location information degrades. Another aspect of our protocol is that it can be spatially dependent - meaning different physical areas of the network can be using quite different routing procedures at the same epoch. That our protocol can dramatically increase scalability can be measured via the routing control overhead which we show, through analysis and simulation, to be significantly reduced relative to current protocols. This is particularly so when a large fraction of nodes possess up-todate accurate location information. Our new protocol operates even though nodes can be mobile, and it provides an enhanced, yet pragmatic, location-enabled solution that can be deployed in all emerging wireless ad hoc networks. <s> BIB007 </s> A Survey of Abnormal Traffic Information Detection and Transmission Mechanisms in VSNs <s> Routing-Based Multihop Transmission. <s> Solutions for Vehicular Ad-Hoc Network (VANET) are challenging due to the intrinsic nature of the network which involves, by definition, node mobility, scarce or null fixed nodes and, at the current state of art, lack of solutions for the real-time tracking of positions. Moreover VANETs are meant to provide primarily a solution for the improvement of road safety, by the proper forwarding of messages: this makes the overall service scenario even more critical due to the delay-constraints and the scalability issues. <s> BIB008 </s> A Survey of Abnormal Traffic Information Detection and Transmission Mechanisms in VSNs <s> Routing-Based Multihop Transmission. <s> This paper focuses on intelligent transportation systems and, more precisely, on intervehicle ad hoc networks. A vehicular ad hoc network (VANET) is a highly dynamic network as the vehicles communicate using short-range wireless communications and can move very quickly. Thus, for example, we can only rely on short interactions between vehicles to exchange information about relevant events. In this paper, we describe in detail a dissemination protocol that vehicles can use to share information by using vehicle-to-vehicle communications. The dissemination approach considers the relevance of the data, represented by what we call encounter probability, to decide when a rediffusion is needed. The protocol is able to disseminate data about any type of event in the network (e.g., available parking spaces, accidents or obstacles in the road, information about moving objects such as emergency vehicles that should get the right of way, etc.) by setting appropriate weights for the different factors that affect the computation of the encounter probability. An extensive experimental evaluation with different types of events shows the interest of the proposal: The vehicles receive the relevant messages in time, and the network overload is limited. <s> BIB009 </s> A Survey of Abnormal Traffic Information Detection and Transmission Mechanisms in VSNs <s> Routing-Based Multihop Transmission. <s> Vehicular sensor networks are an emerging network paradigm, suitable for various applications in vehicular environment making use of vehicles' sensors as data sources and Inter-Vehicle Communication systems for the transmissions. We present a solution, based on vehicular sensor networks, for gathering data from a certain geographic area while satisfying with a specific delay bound. The method leverages the time interval during which the query is active in order to make the gathering process efficient, properly alternating data muling and multi-hop forwarding strategies like in delay-bounded routing protocols. Simulations show that our proposed solution succeeds in performing efficient data gathering outperforming other solutions. <s> BIB010 </s> A Survey of Abnormal Traffic Information Detection and Transmission Mechanisms in VSNs <s> Routing-Based Multihop Transmission. <s> Many applications in vehicular networks are context-aware in that the observations of sensing nodes, potentially vehicles, at a target location should be made available to the requesting node possibly at a different location. In order to provision such applications, two phases of packet routing between the requesting node and the target location and packet dissemination within the target location need to be implemented. In this paper, we focus on the second phase and propose an efficient reliable packet dissemination mechanism, Request-adaptive Packet Dissemination Mechanism (RPDM), in target location. RPDM allows for different applications to generate request packets based on their exclusive observation needs and delay requirements and adapts the dissemination mechanism in target location to specific needs of the request packet received. Besides, RPDM also takes the intrinsic characteristics of vehicular environments into account to make sure roadmap and connectivity constraints are considered and broadcast storm is prevented. Finally, RPDM is compared with a best-known state-of-the-art data dissemination mechanism, COR, and the results show that RPDM outperforms COR in terms of both resolution time and packet overhead traffic. <s> BIB011
According to the transmission strategy, the existing multihop routing technologies in VSNs can be classified into broadcast, multicast, and unicast. From the perspective of routing information, all the multihop routing protocols can be divided into topologybased routing, location-based routing, DTN-based routing, and hybrid-style routing. The detailed classification results have been shown in Figure 6 . (a) Transmission Strategy (i) Broadcast. "Broadcast" aims at delivering information to all vehicle nodes. The traditional flooding-based broadcast methods easily cause broadcast storm problems. To address this issue, most broadcast protocols in VSNs focus on reducing message redundancy and optimizing the selection of rebroadcast nodes. For example, a content-based dissemination protocol for VANETs is proposed in BIB009 , which defines an eventrelated degree parameter to indicate the encounter probability between vehicle node and event. The last broadcast vehicle node selects the neighbor node that has the highest event-related degree value to be the next rebroadcast node. In this way, the event information can only be transmitted to potential users, so the total number of rebroadcast nodes decreases. In BIB004 , a cross layer broadcast protocol for multihop emergency message dissemination is proposed based on the handshaking mechanism. In order to restrict the total number of rebroadcast nodes in the whole network, it optimizes the selection of next rebroadcast node by comparing some information like distance, speed, channel condition, and so forth. Moreover, the handshaking mechanism can prevent much unnecessary information rebroadcasting operations. In BIB005 , the authors propose a fast and reliable emergency message dissemination mechanism. It divides the road into multiple small segments of equal areas according to the vehicle density. The minimal waiting time slot is assigned to the vehicle node located in the farthest road segment. This idea is repeatedly used to handle the broadcast storms, but it still may produce the spatial broadcast storm problem BIB003 . To this, the idea of ring-based road division is first raised in BIB006 , where the width of each ring is computed based on the density of neighbor vehicles. The vehicle nodes in the farthest ring will be assigned the shortest waiting time. (ii) Multicast. "Multicast" aims at delivering information to multiple vehicle nodes. It includes cluster-based routing and geographic broadcast (geocast) routing. In cluster-based routing, the objects of multicast are all the nodes in each cluster structure. And the formation of cluster structure is based on the vehicle ID, the relative mobility between vehicles, or the composite information of vehicles. For example, the COIN BIB007 protocol utilizes the mobility, position, and behaviors of vehicle nodes to build the cluster structure. In geocast routing, the objects of multicast are all nodes in the targeted geographic area, which is also called the zone of relevance (ZOR). To reduce the communication overhead and avoid the network congestion, the zone of forwarding (ZOF) is designed to limit the flooding range. At first, the message is transmitted to the ZOF by the unicast routing. When the message has arrived in ZOR, it will be delivered to all the other vehicle nodes by the flooding method. The most classic geocast routing protocols include IVG BIB001 , cached geocast BIB002 , and abiding geocast  . In BIB008 , the Mapcast protocol is proposed based on the mutual positions of nodes and the CSMA/CA MAC mechanisms. It extends the intuitive concepts of Geo-Broadcast towards a more precise idea of Map-Driven forwarding, where the real life road topology leads the forwarding policies. (iii) Unicast. "Unicast" aims at delivering information to the specified vehicle node. It is widely applied in the data gathering and publish/subscribe systems. Actually, data gathering International Journal of Distributed Sensor Networks 7 can be thought of as a special publish/subscribe system initiated by the sink node. For instance, Palazzi et al. exploit the base station (BS) to create request packets and continuously broadcast them in BS coverage area BIB010 . Then, those vehicle nodes driven into BS coverage area and received request packets will become specified target vehicle nodes. They are responsible for gathering and replying interest information for BS. In BIB011 , Shafiee et al. propose a request-adaptive packet dissemination mechanism (RPDM). Firstly, it asks the subscribe node to disseminate the request packets until finding the target nodes conforming to the return condition (RC). Then, the reply mechanism is triggered by target nodes. To expand the environment sensing area, RPDM designs more flexible RC structure, which can be adaptive to different RC types and delay conditions.