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Effective and robust routing protocol, as well as security and privacy are critical issue for the deployment of vehicular ad hoc networks. Efficient and easy-to-manage routing protocol and their security and privacy-enhancing mechanisms are essential for the wide-spread adoption of the VANET technology. In this paper, we are trying to overcome with this problem, and in particular, how to accomplish efficient and robust routing protocol. We examine the possible attacks and security issues in routing protocol and their security solutions. Our proposal enables vehicle on-board units to generate their own pseudonyms, without affecting the system security. We design mechanisms that reduce the security overhead for safety beaconing, and preserve robustness for transportation safety, even in adverse network settings. Furthermore, we show how to enhance the security in VANET through securing the routing protocol.
Security, vehicular ad hoc networks, routing protocol
Vehicular networks are sets of surface transportation systems that have the ability to communicate with each other. Vehicular ad hoc networks (VANETs) are the networks which are formed according to the appearance and movement of vehicles and its consist of a set of moving objects witch communicate with each other using wireless networks like IEEE 802.11 and Ultra Wide Band (UWB) . Vehicular ad hoc networks (VANET) enable vehicles to communicate among them (V2V communications) and with roadside infrastructure (V2I communications). Such networks present diverse functionalities in terms of vehicular safety, location based service (LBS) , and traffic congestion reduction applications. Identify the potential of VANET, there have been concentrated efforts to network vehicles. However, many challenges including the security and privacy in routing protocol issues remain to be addressed. The design of routing protocols in VANETs is an important and necessary issue to support the smart ITS (Intelligent transportation system). In this paper, we have mainly analysis different routing protocol results in VANET. We introduce different routing protocol (unicast protocol, multicast protocol, geocast protocol, Mobicast protocol, and broadcast protocol) in VANET network . Position-based routing (PBR) provides scalable and efficient (unicast) forwarding in large-scale and highly volatile ad hoc networks, in contrast to topology-based ad hoc routing. Position-based routing is currently considering and evaluated by the Car2Car Communication Consortium. Position-based routing, described basically comprises a location service that maps a given node ID to its current position, geographic (unicast)
communication, and distribution of data packets in geographic areas. These services, in addition to single-hop broadcast, enable road safety applications that disseminate safety information either as 'event-driven messages' hazard warning) or 'periodically-sent beacons' (e.g. Extended electronic brake-light, forward collision warning). It is observed that carry-and-forward data is the new and key consideration for designing all routing protocols in VANETs. With the contemplation of multi-hop forwarding and carry-and-forward data techniques, min-delay and delay-bounded routing protocols for VANETs are discussed in this paper. Besides, the impermanent network fragmentation problem and the broadcast storm problem are further measured for designing routing protocols in VANETs. The provisional network fragmentation problem caused by quickly changeable topology influence on the performance of data transmissions. The broadcast storm problem critically affects the successful rate of message delivery in VANETs. It is important to secure communication in VANETs, otherwise the benefit of VANET networks can turn into a terrifying: an attacker could send false information to other nodes (vehicle), or block others from receiving safety messages. Since periodic safety messages are single-hop broadcasts, the focus has been mostly on securing the application layer. For example, the IEEE P1609.2 draft standard  does not consider the protection of multi-hop routing. However, when the network operation is not secured, an attacker could easily partition the network and make delivery of event-driven safety messages impossible. For example, the attacker could advertise a lot of false identity/position pairs to its neighbors, thus forcing them to believe there are many neighbors. It is highly probable packets are lost when forwarded to non-existent nodes. The major challenge is to conquer these problems to provide routing protocols with lower communication overhead, the low communication delay, and the low time complexity with secure data transitions.
2. VEHICULAR NETWORK : ROUTING IN VANET NETWORK
A routing protocol governs the way that two communication entities exchange information with each other, by establishing a route, making decision for forwarding the data packets and maintaining the route or recovering from routing failure . Routing in VANET has been studied and investigated widely in the past few years [22-25]. Since VANETs are a speciï¬c class of ad hoc networks, the commonly used ad hoc routing protocols initially implemented for MANETs have been tested and evaluated for use in a VANET environment. Use of these addresses-based and topology-based routing protocols requires that each of the participating nodes be assigned a unique address. This implies that we need a mechanism that can be used to assign unique addresses to vehicles but these protocols do not guarantee the avoidance of allocation of duplicate addresses in the network . Thus, existing distributed addressing algorithms used in mobile ad-hoc networks are much less suitable in a VANET environment. Speciï¬c VANET-related issues such as network topology, mobility patterns, demographics, density of vehicles at different times of the day, rapid changes in vehicles arriving and leaving the VANET and the fact that the width of the road is often smaller than the transmission range all make the use of these conventional ad hoc routing protocols inadequate.
In general, a personal vehicle exhibits the following properties:
a. As we have just seen, a vehicle may have high communication capabilities, depending on the interface cards installed in the OBU.
b. Vehicles are equipped with long-lived batteries, so the energy consumption due to communications is almost negligible.
c. Memory and computational resources are high enough to develop complex algorithms. Here, memory and CPU savings are not a critical concern.
d. Position information may be acquired via geographic positioning systems like GPS.
e. Vehicles can have digital maps of the geographic zone they are travelling around. Moreover, they might be aware of the route that is to be followed.
3. Different Routing Protocols for Vehicular Ad-hoc Networks:
Routing protocols in VANETs, are mainly classified in source routing or geographic routing.
3.1 Source. Routing. Based. Protocols.
3.1.1 Geographic Source Routing (GSR)
The principal idea of GSR protocol is to use the knowledge of the street map of the area where the nodes are moved using a static street map and location information about each node. This information is found in the navigator device on the vehicle. When the topology is known, the protocol can apply Dijkstra's algorithm to discover the shortest path to the destination. Then the message is sent to the closer one hop neighbor. The message can be lost if there are very few nodes, and so the connection is low. This protocol has another problem, as it uses a global initial flooding to determine the location of the destination, thus, the scalability is not guaranteed.
3.1.2 Spatial Aware Routing (SAR)
In SAR, a node determines its location on the spatial model and uses the street information to calculate a shortest path to a packet's destination. When this path is determined, the set of geographic locations to be traveled is embedded into the header of the packet. This protocol introduces a way to avoid losing packets and uses GSR as the basis, but this protocol finds an alternative route to that previously found Dijkstra in the source node. First, it finds the shortest path; then it uses the Dijkstra algorithm again after eliminating the edge representing the current street. Thus, another optional path can be found. SAR has a good packet reception radio.
3.1.3 Anchor based Street and Traffic Aware Routing (AZSTAR)
The A-STAR algorithm uses anchor-based unicast routing, which involves inserting a sequence of geographic forwarding points into a packet, through which the packet must travel on its route to the destination. This protocol uses a static street map to route messages around potential radio obstacles. All this information is used to compute an anchor path using Dijkstra's least weight path algorithm.
Packets are routed through alternative paths when routing has problems. Streets with problems are marked as out of service. The packet contains information about the recently discarded street, and uses this information to choose a new route. This information is valid only during some time, since they can be outdated.
3.1.4 Connectivity Aware Routing (CAR)
This protocol has the ability to maintain a cache of successful routes between various sources and destination pairs. Also it predicts positions of destination vehicles, repairs routes as those positions change, and employs geographic marker messages. It uses a preliminary flooding based phase to localize the destination node. So, a new adaptive beaconing mechanism is introduced to maintain the overhead of control messages independently of the density of the network. Establishing the notion of a guard, a geographic marker message that is buffered and passed from one vehicle to another to proliferate forwarding about a node that has moved to a new location. There are two forms of guards: standing guard, which is tied to specific geographic coordinates and travelling guard which has initial coordinates, initial time and velocity vector.
3.2 Geographic Routing Based Protocols (GRBP)
Geographic routing protocols are most used in vanet network .these protocols are only used to transmit messages between vehicles in the same street,or on the same road . These protocols do not use source routing, and the main idea is to use geographic routing directly over the map streets, that helps to take decisions about new directions.
3.2.1 Greedy Perimeter Coordinator Routing (GPCR)
GPCR eliminates the precondition that assumes that each node knows the complete street map, and does not use flooding. This protocol improves upon GSR by eliminating the requirements of an external static street map. Seeking to minimize potential radio obstacles, this protocol modify the typical destination based greedy forwarding strategy such that there are only route messages along streets. In this way, routing decisions are only made at street intersections.
3.2.2 Vehicular Assisted Data Delivery (VADD)
VADD is based on the idea of carrying and forwarding. The most important issue is to select a forwarding path with the smallest packet delivery delay. This protocol requires each vehicle to know its own position and also requires an external static street map that includes traffic statistics.
Thus, VADD follows the following basic principles:
• Transmit through wireless channels as much as possible.
• If the packet has to be carried through certain roads, the road with higher speed should be chosen.
3.3. Trajectory. Based. Protocol
Currently, most of the vehicles are equipped with GPS technology to determine its position. Also, with Internet connection, these devices support periodical updates of information such as traffic, street closed, weather, location of restaurants, etc. This information can be useful for a routing protocol.
3.. 3.1 Trajectory Based Forwarding (TBF)
Trajectory Based Forwarding (TBF) is a novel method to forward packets in a dense ad-hoc network that makes it possible to route a packet along a predefined curve. The routing process consists of selecting as next relay the neighbor which is closer to a point in the curve.
There are some aspects to carefully consider. First, there are several different
The characteristics used to define the best neighbors at each step:
• The neighbor closest to the curve on a straight line.
• The neighbor whose closest point of the curve provides the greatest advance along the curve.
• The node closest to the centroid of candidate neighbors.
• A neighbor randomly chosen among the best three.
3.3.2 Opportunistic Geographical Routing (GeOpps)
The GeOpps protocol assumes that the source node already knows the position of the destination of some kind of location database or similar approach. Also it assumes that cars can interchange their expected routes using beacon messages. Nodes in this protocol follow a predefined trajectory; they use the expected trajectory of the neighbors to take routing decisions. The general idea is that if a node finds a
Neighbors whose trajectory go closer to the destination's position that its own, it sends the packet to that node.
When a message is being sent from a source node to a destination using GeOpps, intermediate nodes use the following method to select the next hop. Each neighbor vehicle that is following a navigation suggested route calculates its future nearest point to the message destination. It also uses a utility function built into its navigation system to calculate the amount of time required to reach that point. The vehicle that can deliver the packet fastest or closest to the destination will be chosen as the next hop for the message. By choosing nodes whose trajectory go closer and closer to the destination coordinates, it is expected that data packets will eventually make it to the destination.
3.3.3 QoS (Quality of Service)
Currently, routing protocols in VANETs cannot provide a complete QoS. In the strictest sense, a QoS protocol should provide guarantees about the level of performance provided. This is often achieved through resource reservation and sufficient infrastructure. However, in an ad-hoc wireless network, this is a difficult task. With the exception of the potential for roadside units, there is no infrastructure to be relied upon for guaranteed bandwidth.