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
daljeetmotton91p@gmail.com, 2
arvind_uiet@yahoo.co.in
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. CHARACTERISTICSOF 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.

NITTTR, Chandigarh EDIT -2015 106
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

107 NITTTR, Chandigarh EDIT-2015
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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