An Introduction of VANET
VANET is a type of MANET, which is a group of mobile, wireless nodes which cooperatively and spontaneously form an IP-based network. This network is independent of any ﬁxedinfrastructure or centralized administration. A node communicates directly with nodes within its wireless communication range. Nodes that are part of the MANET, but beyond each other’s wireless range communicate using a multi-hop route through other nodes in the network. These multi-hop routes change with the network topology and are determined using a routing protocol such as DSDV, DSR, AODV, TORA, ZRP, etc.
Vehicular Ad Hoc Networks (VANETs) have been proposed as a technology that will enable connectivity of users on-the-move and also implement Intelligent Transportation Systems(ITS). In VANETs, nodes can not freely move around an area or surface; their movements are restricted within the roads formed around obstacles such as buildings.
VANET is used to provide communication among nearby vehicles and between vehicles and nearby fixed equipment, usually described as roadside equipment, usually described as roadside equipment. VANET technologies aim at enhancing traffic safety for drivers, providing comfort for passengers, or reducing transportation time and fuel consumption with many potential applications. VANET is a technology that uses moving cars as nodes in a network to create a mobile network. VANET turns every participating car into a wireless router or node, allowing cars approximately 100 to 300 meters of each other to connect and, in turn, create a network with a wide range. One of the greatest challenges of VANETs is to establish cost-effective connections between vehicles and vehicles or between vehicles and roadside units (RSUs).
A new VANET-based Smart PARKing (SPARK) scheme to provide drivers with convenient parking services in large parking lots. The SPARK scheme is characterized by employing parking lot RSUs to surveil and manage the whole parking lot usingVANET communication technology.SPARK scheme provides VANET-based intelligent anti-theft protection service, provides real-time parking navigation service to drivers in large parking lots, and provides friendly parking information dissemination service to the moving vehicles.
VANET is an emerging technology to achieve intelligent inter-vehicle communications, seamless internet connectivity resulting in improved road safety, essential alerts, and accessing comforts and entertainments. The technology integrates WLAN/cellular and Ad Hoc networks to achieve continuous connectivity.
Broadcasting in vehicular ad hoc networks (VANET) is emerging as a critical area of research. One of the challenges posed by this problem is the conﬁnement of the routing problem to vehicle-to-vehicle (V2V) scenarios as opposed to also utilizing the wireless infrastructure (such as cellular networks). At a fundamental level, safety and transport efﬁciency is a mandate for current car manufacturers and this has to be provided by the cars on the road as opposed to also using the existing wireless communications infrastructure.
VANET suggests unlimited advantage to companies of any size. Vehicles access to fast speed internet which will change the automobiles’ onboard system from an effective widget to necessary productivity equipment, making nearly any internet technology accessible in the car. Thus this network does pretend specific security concerns as one problem is no one can type an email during driving safely. This is not a potential limit of VANET as productivity equipment. It permits the time which has wasted for something in waiting called “dead time”, has turned into the time which is used to achieve tasks called “live time”.
If a traveler downloads his email, he can transform jam traffic into a productive task and read the on-board system and read it himself if traffic stuck. One can browse the internet when someone is waiting in the car for a relative or friend. If GPS system is integrated it can give us a benefit about traffic related to reports to support the fastest way to work. Finally, it would permit for free, like Skype or Google Talk services within workers, reducing telecommunications charges.
The main goal of VANET is to provide safety and comfort for passengers. To this end, special electronic devices will be placed inside each vehicle which will provide an Ad-hoc network and server communication. Each vehicle equipped with a VANET device will be a node in the ad-hoc network and can receive and relay others messages through the wireless network. There are also multimedia and internet connectivity facilities for passengers, all provided within the wireless coverage for each car.
Characteristics of VANET
- Rapid topology changes and frequent fragmentation, resulting in small effective network diameter
- Virtually no power constrains
- Variable, highly dynamic scale and network density
- The driver might adjust his behavior reacting to the data received from the network, inflicting a topology change
High Dynamic topology: The speed and choice of path define the dynamic topology of VANET. If we assume two vehicles moving away from each other with a speed of 60 mph ( 25m/sec) and if the transmission range is about 250m, then the link between these two vehicles will last for only 5 seconds ( 250m/ 50ms-1). This defines its highly dynamic topology.
Frequent disconnected Network: The above feature necessitates that in about every 5 seconds or so, the nodes needed another link with a nearby vehicle to maintain seamless connectivity. But in case of such failure, particularly in the case of low vehicle density zone, frequent disruption of network connectivity will occur. Such problems are at times addressed by road-side deployment of relay nodes.
Mobility Modeling and Prediction: The above features for connectivity, therefore, needed the knowledge of node positions and their movements which as such is very difficult to predict keeping in view the nature and pattern of movement of each vehicle. Nonetheless, a mobility model and node prediction based on a study of predefined roadways model and vehicle speed are of paramount importance for effective network design.
Communication Environment: The mobility model highly varies from highways to that of the city environment. The node prediction design and routing algorithm also, therefore, need to adapt to these changes. The highway mobility model, which is essentially a one-dimensional model, is rather simple and easy to predict. But for the city mobility model, street structure, variable node density, presence of buildings and trees that behave as obstacles to even small distance communication make the model application very complex and difficult.
Features of VANET
- The nodes in a VANET are vehicles and roadside units
- The movement of these nodes is very fast
- The motion patterns are restricted by road topology
- The vehicle acts as a transceiver i.e. sending and receiving at the same time while creating a highly dynamic network, which is continuously changing.
- The vehicular density varies from time to time for instance their density might increase during peak office hours and decrease at night times.
Application of VANET
Three major classes of applications possible in VANET are
- Safety oriented
- Convenience oriented
- Commercial oriented
Routing protocols in VANET
- Ad-hoc routing
- Position-based routing
- Cluster routing
- Broadcast-based routing
- Geocast based routing
Ad-hoc routing: AODV (Ad Hoc on-demand distance vector) and DSR (Dynamic source routing) are therefore can be applied to VANET. However, the simulation of these algorithms in VANET brought out frequent communication breaks which is mainly attributed to the high dynamic nature of its nodes. To meet the VANET challenges, these existing algorithms are suitably modified.
The following application in their model:
- A highly partitioned highway scenario is used where most path segments are relatively small.
- The initial simulation with the AODV algorithm resulted in frequent link breaks as expected, owing to the dynamic nature of the node’s mobility.
- Two predictions are added to AODV to upgrade the algorithm.
- In one, node position and their speed information are fed in AODV to predict link lifetime. This is referred to as PR-AODV and it constructs a new alternate link before the end of the estimated link lifetime. (In AODV, the link created only after the failure of connectivity occurs).
- In second modified algorithm (PRAOVD-M), it computed the maximum predicted lifetime among various route options (in contrast to selecting the shortest path as in PRAODV or AODV).
- The simulation on both showed an improved packet driving ratio.
- However, the success of this algorithm largely depends on the authenticity of node position and mobility.
In another model, AODV is modified to forward the route request within a zone (rectangular or circular) of relevance (ZOR) from the point of event occurrence to make the algorithm more effective.
Position-based Routing: The technique employs the awareness of vehicles about the position of another vehicle to develop the routing strategy. One among the best-known position-based routing is GPSR (Greedy Perimeter Stateless Routing) which works in the principle of combining greed forwarding and face routing. This algorithm has the following advantages and constraints.
- It works best in open space scenarios (Highways) with evenly distributed nodes. The absence of fewer obstacles in highway scenarios is attributed to its good performance.
- The comparison of simulation results of GPSR from that of DSR in highway scenarios is generally considered to be better.
- In city condition, GPSR suffers from many problems:
- Greedy forwarding is restricted owing to obstacles
- Routing performance degrades because of longer path resulting in higher delays
- Node mobility can induce routing loops for face routing
- The packet can at times be forwarded in the wrong direction resulting in higher delays
Cluster-based routing: In cluster-based routing, several clusters of nodes are formed. Each cluster is represented by a cluster head. Inter-communication among different clusters is carried through cluster heads whereas intra-communication within each cluster is made through the direct link. This cluster algorithm, in general, is more appropriate for MANET. But for VANET, owing to its high speed, and unpredictable variation of mobility, the continuity of link in the cluster often breaks. Certain modification in the algorithm (COIN – Clustering for Open IVC Network put forth by Blum et al.LORA-CBF – Location-based Routing Algorithm using Cluster-based Flooding suggested by Santos et al.) such as the incorporation of a dynamic movement scheme, expected decisions of a driver under a certain scenario, enhancing the tolerance limit of inter-vehicle distances are included that on are observed to provide more stable structure at the cost of little additional overhead.
Broadcast-based Routing: This is the most frequently used routing protocol in VANET especially to communicate safety-related messages. The simplest broadcast method is carried by flooding in which each node rebroadcasts the message to other nodes. This ascertains the arrival of messages to all targeted destinations but has a higher overhead cost. Moreover, it works well with a lesser number of nodes in the network. A larger density of nodes causes an exponential increase in message transmission leading to collisions, higher bandwidth consumption, and a drop in overall performance. Several selective forwarding schemes such as BROADCOMM (by Durresi et al.), UMB (Urban Multihop Broadcast Protocol), Vector-based Tracking Detection (V-TRADE), History Enhanced V-TRADE (HV-TRADE), etc are proposed to counter this network congestion.
- BROADCOMM Scheme: In this, the highway is segmented to define virtual cells which move along with the vehicles. Only the selected few nodes in each virtual cell ( cell reflectors) are responsible for handling messages within its cell nodes and forwarding / receiving the messages to/ from neighboring cell reflectors. The protocol works well with a smaller number of nodes with a simple highway structure.
- UMB: In UMB protocol, each node while broadcasting the message, assigns only the farthest node to forward the message (rebroadcast). At the street intersections, repeaters are installed to forward the package to all road segments. This scheme has a higher success ratio and also can overcome interference, packet collisions, etc. to a great extent.
- V-TRADE / HV-TRADE: This scheme is a GPS-based protocol. Based on position and movement information, each node classifies its neighboring nodes into different groups and while forwarding the message to neighboring nodes, it assigns only a few border nodes of each group to forward the packets. Because of the lesser number of nodes assigned for multi-hopping, it indicated significant bandwidth utilization.
- Geocast based Routing: It is a location-based multicast routing protocol. As the name implies, each node delivers the message/ packet to other nodes that lie within a specified geographic region predefined based on ZOR (zone of relevance). The philosophy is that the sender node need not deliver the packet to nodes beyond the ZOR, as the information (related to the accident, important alerts for example) would have the least importance to distant nodes. The scheme followed a directed flooding strategy within a defined ZOR so that it can limit the message overhead.
KEY MANAGEMENT FOR SECURE VANET
Key management mechanisms for secure VANEToperation turn out to be a surprisingly intricate and challenging endeavor, because of multiple seemingly conflicting requirements. On one hand, vehicles need to authenticate vehicles that they communicate with; and road authorities would like to trace drivers that abuse the system. On the other hand, VANETs need to protect a driver’s privacy. In particular, drivers may not wish to be tracked down wherever they travel.
A VANET key management mechanism should provide the following desirable properties:
Authenticity: A vehicle needs to authenticate other legitimate vehicles, and messages sent out by other legitimate vehicles. A vehicle should filter out bogus messages injected by a malicious outsider and accept only messages from legitimate participants.
Privacy: RSUs and casual observers should not be able to track down a driver’s trajectory in the long term. Authorities can already trace vehicles through cameras and automatic license-plate readers, however, VANETs should not make such tracing any simpler. The privacy requirements seemingly contradictory to the authenticity requirement: suppose each vehicle presents a certificate to vouch for its validity, then different uses of the same certificate can be linked to each other. In particular, suppose a vehicle presents the certificate to an RSU in one location; and later presents the same certificate to another RSU in a different location. Then if these two RSUs compare the information that they have collected, they can easily learn that the owner of the certificate has traveled from one location to another.
Traceability and Revocation: An authority should be able to trace a vehicle that abuses the VANET. In addition, once a misbehaving vehicle has been traced, the authority should be able to revoke it in a timely manner. This prevents any further damage that the misbehaving vehicle might cause to the VANET.
Efficiency: To make VANETs economically viable, theOBUs have resource-limited processors. Therefore, the cryptography used in VANET should not incur heavy computational overhead.
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