a review report on existing routing protocols in vehicular ad hoc networks (vanets)

Int. Journal of Electrical & Electronics Engg. Vol. 2, Spl. Issue 1 (2015) e-ISSN: 1694-2310 | p-ISSN: 1694-2426

105 NITTTR, Chandigarh EDIT-2015

A Review Report on Existing Routing Protocols in Vehicular Ad Hoc Networks

(VANETS)

Daljeet Singh Motton1, Arvind Kumar2

Department of Electronics and Communication UIET, Panjab University Chandigarh, India 1 [email protected], [email protected]

Abstract—Vehicular ad hoc networks (VANETs) are an extension to the mobile ad hoc networks (MANETs) that have been designed with the goal of providing vehicular safety, traffic monitoring, assisting vehicular driving by providing critical information, utility services viz. automatic road taxes, finding hospitals, fuel stations, restaurants etc. The primary characteristics of VANETs include high node mobility, no specific network infrastructure, irregular network environments and unpredictable network density. Choosing a routing protocol for the VANET environment is a critical step in devising data sharing scheme for the VANET. This paper studies the existing routing protocols for VANET and presents a precise review of merits and demerits of the same. Keywords: VANET, vehicular networks, topological routing protocols, geographical routing protocols.

I. INTRODUCTION Vehicular ad hoc networks (VANETs), the extension of MANETs, unlike the conventional ad hoc networks have highly distinguishing characteristics like high node mobility, frequent construction and destruction of network, relative speed of network nodes, unpredictable network densities and various other factors [1]. In the recent years, it has been observed that there is exponential increase in the number of on-road private vehicles which has led to the rise in the number of road accidents and hence the on-road deaths [2]. It has been found that the cause for the larger proportion of the road accidents is the inability of the driver to take the timely action according to the situation which is limited by the ability of human beings to perceive things correctly and act. However, accurate and timely information to the driver can prevent the accident from happening. VANET facilitates this by providing critical information to the driver, so that timely action can be taken. Choosing a routing protocol while designing the vehicular network is of very high importance as all other factors like packet delay, traffic overload, efficiency of the network depends upon the routing protocol operational in the vehicular network [3].

Finally, conclusion and references are presented in section IV.

II. VANET

VANET (vehicular ad hoc network) refers to the ad hoc network formed by the vehicles traveling on the road. The network is called ad hoc as it does not require any infrastructure like fixed wired routers etc. The vanet has only two components involved in the communication. The first is an on board unit (OBU) which is a wireless device that acts as transceiver and has facilities like GPS installed on it. The second being road side unit (RSU) which is a stationary antenna placed on the road side. The stationary component of vanet is mainly used for the one- to-one communication between vehicle and antenna, or is sometimes used for broadcasting messages to the vehicles i.e. mobile component of vanet [4]. Due to these components three scenarios are feasible for vanet. The pure cellular network is a connection between the moving vehicle and the road side unit only. The scope of communication is limited by the range of the RSU and is mainly used for the broadcasting of the messages and the synchronization. The second scenario consists of all the road vehicles communicating among themselves thus forming an ad hoc network. The scope of communication always exists as long as the vehicle is in the transmission range of another vehicle. The third scenario is amalgamation of the two pure forms of communications [1]. As the third scenario is hybrid of the other two, it provides superior solution to the problem of communication.

III. CHARACTERISTICS OF VANET The vehicular ad hoc network consists of a number of similar yet distinct characteristics. The vanet is defined in terms of its characteristics completely [4]. The several characteristics of vanet are discussed below. Highly dynamic topology: The network topology in vanet is highly dynamic due to the motion of participating vehicles in the network. Communication environment: It is always arbitrary i.e. the features of the network environment cannot be predicted. City scenario and highways scenarios is two communication environment. Interaction among on-board units: It consists of sharing critical information, essential announcement or a product advertisement or any utility service indication, among OBUs. Energy of mobile network nodes: Higher the node energy the longer can the message be transmitted whereas

This review paper provides an overview of VANET and existing routing protocols for the same, so that a prudent decision can be made while choosing a routing protocol for the vehicular network. The paper is organized as follows. Section II gives the overview of the VANET and its different characteristics, section III gives brief but precise view of the routing protocols proposed for VANET. Section IV discusses the issues and application domains of the existing routing protocols.


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low energy node cannot transfer data to longer distances. Network density: It is the number of vehicles in the specific area, that trying to communicate or an active member of the network. Most routing protocols are either suited for the highly dense or low density network, but no routing protocol has efficient performance over variable density networks. Frequent connection/disconnection of vehicular nodes is the breaking and making of the network links. Different node mobilities lead to the instability of the vehicular environments. Few vehicles are fast and other may be slow, that leads to frequent connection/disconnection of the environments. DATA DISSEMINATION IN VANET The data can be broadcasted, geocasted or the network may exhibit cluster based routing [1]. The broadcasting is like general way of broadcasting. In geocast routing the data dissemination is localized to some specific area or area concerned with the information. The cluster based routing divides whole network into the sub-networks called clusters.

IV. ROUTING PROTOCOLS IN VANET The routing protocols in VANET can be broadly classified into two groups: topological routing protocols that use the information contained in the link among nodes and geographical routing protocols that utilize position of the vehicular nodes in order to communicate with them. The node information can be obtained from the installed devices on the on board units called as GPS or other location determining devices.

Topological Routing Protocols These consist of proactive & reactive routing protocols. Proactive routing protocols maintain information about the links irrespective of its requirement i.e. it is not necessary that the information maintained will be used whereas Reactive routing protocols generate the information only when there is requirement of information.

Reactive Routing Protocols Ad hoc on demand distance vector routing protocol (AODV) [5] enables network to generate link information only if needed. Conventional routing tables store the link information. Source node initiates route discovery phase the Route Request packets (RREQ) are broadcasted, neighbour nodes not knowing destination further broadcast route request packets. The nodes that know about the destination reply back to the source node using Route Reply (RREP) packet; this packet is received by the source node that establishes the route and starts the data transmission. Ad hoc on Demand Multipath Distance Vector Routing Protocol (AOMDV) [6] an extension to AODV protocol has main application in calculating multiple loop free and link disjoint paths. The performance of AOMDV is much better than the AODV protocol. The AOMDV can find node disjoint. The AOMDV routing protocol is used for the scenarios that have highly mobile nodes. AODV extension using Ant Colony Optimization [7] an extension of AODV is a metaheuristic search protocol that performs well in ad hoc network. The mixture of goodness of ant colony and the repairing strategy of

AODV gives a highly efficient routing protocol. It has the robustness as it avoids the frequent path losses. Dynamic Source Routing protocol (DSR) [8] employs sequence no. of nodes which are to be traversed for reaching destination. In DSR, the query packet copies in its header part the node ID of the intermediate nodes that it has traversed. Query packet shows the path to the destination which communicates to the source via path. Swarm Intelligence based Routing Protocols [9] focuses on the quality of service required by the VANET. One of the swarm routing protocol QosBee routing protocol is better than AODV and DSDV. Proactive Routing Protocols Fisheye State Routing protocol [10] maintains topology table (TT) constructed using the latest information received from the neighboring nodes. The information is exchanged among network nodes periodically. With decreasing distance the routing tables are updated preferably with the neighbours that are at short distance. Destination sequenced Distance Vector routing protocol (DSDV) [11] based on the bellman ford algorithm was developed by C.Perkins and P.Bhagwat which removes route looping and increases convergence speed helping in reducing control message overhead. Each node has the next hop table that it exchanges with its neighbours. Optimized Link State Routing Protocol (OLSR) [12] given by Clausen and jacquet is an optimization of link state routing protocol used for MANETs. Each node in the network selects set of nodes called multipoint relays (MPR) that retransmit the packets received by it. Reading and processing the packet is only available to the nodes of MPR set. It decreases retransmissions in the network and helps in reducing flooding. HELLO messages are sent to find neighbour nodes. Temporally Ordered Routing Protocol (TORA) [13] based on the link reversal algorithm creates a direct acyclic graph towards the destination. Source node as the root of tree broadcasts data packets to neighbor nodes that rebroadcast the packet based on the DAG. This routing protocol reduces the network overhead as all intermediate nodes don’t need to rebroadcast the message. This routing protocol performs well in dense networks but is not used due to the fact that DSR & AODV perform well than TORA and also because it cannot scaled. Geographical Routing Protocols These use the information about the position of nodes for the data transfer. The differentiating feature of these network routing protocols is that packets are sent towards the destination without any information about the network topology or any kind of prior route discovery. Distance Routing Effect Algorithm for Mobility (DREAM) [14] works on two main principles first uses the position information to connect to the destination or the neighbour node falling in the path to the destination, position information is obtained using the GPS (global positioning system). The other sends data packets by selecting the route node by node until the destination is reached. It generates number of paths from source to destination that are not actually required. It is sensitive to traffic load making it unsuitable for the VANET Greedy Perimeter stateless Routing (GPSR) [15] works on two methods, first is called Greedy Forwarding method in which the source node chooses the optimal neighbour


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as the next hop, the metric used for determining the node to be optimal is the distance i.e. the node at shortest distance to the source node is the optimal node. Due to this greedy behavior, it is named Greedy Forwarding method. The second method is used wherever the packet forwarding is not possible. It is based on the right hand rule in which source node forwards the packet to the first neighbour encountered across the perimeter about itself while traversing in anti-clockwise orientation. It cannot find an optimal route to the destination, increasing the delay and decreasing performance of the protocol. Greedy Perimeter coordinator Routing (GPCR) [16] composed of two methods first is the Greedy Forwarding procedure in which the nodes at the junctions of the roads are marked as the coordinators packet forwarding is done through them. The route from one coordinator to another is decided by the transmitting coordinator based on the traffic density in the path. The second method is the repair strategy that selects the optimal route from the set of available routes. GPCR may not succeed in detecting the junction node which may be at large distance or out of the transmission range. This can’t be used on highways as it wholly depends on the junction nodes. Connectivity Aware Routing (CAR) [17] first locates Preferred Group Broadcasting (PGB) and then finds all connected routes between the source and the destination. PGB is a region limited by the inferior and a superior perimeter in the transmission range of the node that are calculated using the amount of signal power. The routes are maintained by standing and travelling guards. CAR uses the periodical broadcast of the HELLO packets & may result in the flooding of the network. Connectivity-Aware Minimum-Delay Geographic Routing Protocol (CMGR) [18] divides the network into two states viz. sparse and dense. For sparse network, it maximizes the chances of reception so that the packets can be received before it expires. For dense networks, non- congested paths are selected that maintain a threshold level of connectivity over the given time and minimizes the end to end delay. This protocol does not define any repair method. It is more suited to urban city environments. Intersection Based Geographical Routing Protocol (IGRP) [19] finds the route between the source and the destination that has successive road intersections. It forwards packet to the internet gateway by an efficient selection of the road intersections. When a source node needs to transmit a data packet, route discovery is launched by the node to reach internet gateway which is periodically updated and broadcasts the network topology of the current network. Any node connected to the internet gateway can transmit at any time.

V. ISSUES IN EXISTING ROUTING ROTOCOLS Following main issues have been found in the two routing protocols [20]. In Topology Based Routing Protocols the main demerit is the instability of the routes, due to the fact that the routes are severely affected by the high vehicle mobility which also increases the packet drop rate in these protocols. The other demerit is routing overhead created before actually transmitting the data due to HELLO and beaconing messages. This leads to higher requirement of bandwidth and higher delays specifically when the network density is low. This delay is further increased by

the route maintenance and route repairing processes [20]. The topological routing protocols are less suited for the rural scenarios. In Geographical Routing Protocols the primary limitation of the geographical routing protocol is its difficulty in finding the next optimal hop due to the lack of the direct communication among the nodes and due to the presence of the obstacle like trees, big buildings among the vehicular nodes [21]. The use of GPS in determining the exact locations of the vehicles can fail due to atmospheric blockage or failure of the GPS technology [22]. The routing protocols don’t use real time positions of nodes in developing the route strategy and consider only static road map data. APPLICATION DOMAINS OF VANET With VANET as source of critical road information only, it can also be used for a number of other utility services like advertisements, traffic announcements, audio-visual directions. Road taxes can be collected automatically by using information provided by VANET without even actually installing toll plazas on road. In a nutshell VANET can provide plethora of services to the users like infotainment, safety, utility services etc. [23].

VI. CONCLUSION In the recent years, a number of protocols have been developed and each protocol has differentiated characteristics from others. The choice of the routing protocol depends on a number of factors like type of network environment, degree of QoS service like end to end delay, packet overload, required. But still no routing protocol is universal that can be applied to any road environment. The existing routing protocols can be applied to the specific road conditions either alone or in a combination of two or more than two routing protocols which may serve the purpose but may also increase the complexity of the network.

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a review report on existing routing protocols in vehicular ad hoc networks (vanets)

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