This essay has been submitted by a student. This is not an example of the work written by our professional essay writers.
The rapid growth in number of vehicles has led to increase in number of accidents. Companies and researchers have started focusing on designing networks which could improve the road safety and benefit in managing huge traffic. The emergence of new wireless technologies has led to the designing of Vehicular ad-hoc networks which have specific applications in Intelligent transport system or ITS. VANET is a subset of Mobile Ad-hoc Networks which provide communication between vehicles and between vehicles and roads. Protocols used in MANET could not be used in VANET as VANET networks are characterized by high mobility and frequent topology changes. Routing is the most important aspect in VANET. Various routing protocols for VANET have been proposed in the past. A survey on various Intelligent Transportation System (ITS) and various routing protocols is described in this paper.
There has been an enormous increase in the number of vehicles around the world leading to many accidents. The issue of road safety needs special attention. Companies and researchers involved in development of new vehicular technologies have shifted their focus on improving road safety. The development in wireless technologies has led to the emergence of new communications networks which include moving vehicles as part of their nodes. These networks called VANET allow the moving vehicle to communicate with each other and thus directly participating in network.
VANET is a subset of special wireless ad-hoc networks which creates a mobile network using moving vehicles identified as nodes in the network. Many applications can be identified related to road safety where VANET networks have their implementation. Increasing population resulting in increased traffic has led to the problem of congested roads. VANET helps this issue by increasing mobility leading to safe transportation. VANETS provide many benefits to police and drivers and thus helps in preventing accidents and reduce the traffic jams in city. Proper traffic alerts and updated traffic incidents helps to improve traffic and helps in identifying places where traffic rules violations take place. VANET also has economic benefits such as reduction in fuel consumption, trip time and decrease in pollution due to real time traffic alerting.
VANET- APPLICATION IN INTELLIGENT TRANSPORTATION SYSTEM
VANET has many applications in ITS (Intelligent Transportation Systems) also. ITS is an efficient way to improve the flow of vehicles on the roads and also providing comfortable driving, road safety and
distribution of updated information about the road. Various models of ITS have been proposed in the recent years. In  and  two adaptive traffic light systems based on wireless communication between vehicles and fixed controller nodes deployed at squares are designed. Both systems improve traffic fluency, reduce the waiting time of vehicles at squares and help to avoid collision.
Systems that take the control decisions based on the information coming from the vehicles is present in . Every vehicle is equipped with a short range communication device and controller nodes are placed in the intersection with traffic lights. This controller node at intersection acts as adaptive control signal system.
Inter-vehicular communication is presented based on an adaptive traffic control system . This system reduces the waiting time of vehicles at the square also results in reduction in waiting time at the signal. To realize this vehicle the concept of clustering is used to collect the data of the vehicles coming towards the intersection. Clustering algorithm is used to compute density of vehicles within the cluster and sent to the traffic signal controls to set the timing cycle. It uses direction based clustering algorithm. This algorithm is a combination of opportunistic dissemination technique and cluster and it is used to gather the required traffic information. The clusters are created using the direction of the vehicles in a given predefined geographic region approaching the intersection. By employing GPS and digital maps the direction parameter is computed within the vehicles.
VANET ROUTING PROTOCOLS
VANET routing protocols can be classified into two categories namely source routing protocols and geographic routing protocols. In source routing protocol the source node decides the path that message should take to reach the destination whereas in geographic routing protocol the graph of the area decides the path and not the nodes. In this graph next street through which message is to be routed though is chosen. Geographic routing protocols work in two modes: Greedy mode and perimeter mode. In Greedy node the next node selected to forward the message should be the node which is closest to the destination. Perimeter node should be selected in circumstances where greedy mode cannot be applied .
Sometimes a routing protocol called AODV (Ad-hoc on demand distance vector) is used in place of greedy forwarding and geographical routing. Other protocols like Destination Sequence Distance Vector( DSDV) Dynamic Source Routing (DSR) are also there. AODV has advantage over DSR and DSDV as it can handle more packets then two of them because it avoids routes and freshness of routes while DSR uses stale routes. AODV shows higher throughput than DSR and DSDV . The major drawback of AODV is that is requires end to end paths for forwarding the data which is difficult to maintain because in VANETS end to end path does not exist due to high speed of vehicles.
Greedy Perimeter Stateless routing (GPSR) is the basis of all Greedy based protocols in VANET. It was proposed by Brad Karp et al. . GPSR has two modes namely greedy mode and Perimeter mode. The Greedy forwarding mode will forward the message to its one hop neighbour which is closest to the destination as shown in fig.
Fig 2.greedy forwarding mode
Greedy mode works fine as long as there is one hop neighbor closest to the destination but it fails in cases where the current node itself is the closest node possible to the destination and the destination node is not within the coverage area of current node. Whenever the Greedy mode fails GPSR switches to the perimeter node which works on the basis of right hand rule. The right hand is applied to traverse the edges of the void area. This local minimum problem is overcome by picking the next anticlockwise edge and continues to do the same till it reaches the destination. In GPSR a node has to remember the location information of one hop neighbours as against the location information of all nodes maintained at every other node followed by other geographical routing protocols. As GPSR lacks the information about network topology it may get into loops.
Figure 3.perimeter mode
Another protocol which uses the greedy forwarding mechanism was proposed by Lochert. C et al. known as Greedy Perimeter Coordinator Routing (GPCR) . It uses the fact that street map is normally planar thereby reducing the necessity for planarization of graphs. The routing decision is based on the streets and junctions instead of individual nodes and connectivity among these nodes. Each node is identified as either coordinator node or normal node. Nodes in the junctions are coordinator nodes and nodes in the street are normal nodes. GPCR uses two approaches to identify whether the node is in the junction or in the street. In the first approach each node sends a beacon message which consists of the position of the sender as well as its neighbor. Nodes receiving these beacon messages will know the position of its neighbors as well as neighbor's neighbors. If a node 'a' has two neighbors - b and c who are within the transmission range of each other but not listed in their neighbors list then line of sight between these two is hindered by an obstacle, indicating that node 'a' is located in the junction.
Fig 4.coordinator nodes
In the second approach each node calculates its correlation coefficient with respect to its neighbours position. A correlation coefficient of 1 indicates that node is in the street and and 0 indicates that it is in the middle of the street. GPCR does not take into account whether sufficient nodes are in the chosen street to route the message.
Kevin C.Lee et al. in their paper Enhanced Perimeter Routing for geographic forwarding protocols in urban scenarios proposed the protocol GpsrJ+ to improve the recovery strategy in GPSR and GPCR. GpsrJ+ works similar to GPCR but also takes advantage of the situation that it is not necessary for a node to forward the message to the junction node. GpsrJ+ allows the neighbor nodes of the junction nodes to predict the route that junction node would have taken for forwarding the message and forwards the message through the identified route by bypassing the junction node if possible.
Fig 6.Node a forwards to node c without the intervention of junction node
This results in less number of hopes when compared with that of GPCR. This is possible because beacon messages of the node will not only have its own position and neighbor position but also the road segment of the neighbor node.
Kevin C.Lee et al. proposed the Geo Cross protocol to overcome the problem of cross links in GPCR by detecting and eliminating the cross links as well as maintaining the optimal route information at nodes. Geocross eliminates the cross links which occur in perimeter node by piggybacking three fields namely Probe, (UR) Unroutable Roads and VF (visited faces) in the message. When a message is forwarded using perimeter mode to a node, the receiving node checks the probe field for presence of loops. If loop is present then it examines for cross links. In the presence of cross -link the node forwards the message as per the loop so the cross link will be removed. If the adjacent cross link will be present in the loop, the forwarding node decides which forwarding loop is to be removed and the removed route is updated in the UR field so that in future this route will not be used by the forwarding node. The packet delivery ratio of Geo-Cross is higher that of GPSR and GPCR.
VANET - SECURITY RELATED ISSUES
VANET also helps in security issues. Vehicles which are involved in network communication should have a secure communication so that malicious reporter do not provide false information to other vehicles and gain undue advantage. So there is a need for trusted communication between vehicles so that senders identity is authenticated and content of the senders message are not tempered with. An overview of VANET security can be found in . Broadcast communication which means providing senders authentication in broadcast communication is most important challenge in providing security because vehicles might have not before and link-layer loses might affect different broadcast receivers with differing severity. VANET try to solve these issues in a systematic way.
In this paper survey on various Intelligent Transport System and greedy routing protocols is done. Intelligent Transport Systems are used for providing safe transportation and helps in managing huge traffic more efficiently. Also various routing protocols have been discussed and compared. GeoCross and GPSRJ+ found to be more efficient as compared to GPCR and GPSR. These routing protocols are used to implement VANET thus providing features such as increased mobility, traffic alerts, updated traffic information and economic benefits suc as reduction in fuel consumption and reduction in trip time.