In mobile ad hoc networks (MANETs), due to frequent changes in topology there exist more link breakages which lead to high rate of path failures and route discoveries, which cause an increased routing control overhead. Thus, it is necessary to reduce the overhead of route discovery in the design of routing protocols for MANETs. In a route discovery, broadcasting may be an elementary and effective data dissemination mechanism, wherever a mobile node blindly rebroadcasts the first received route request packets unless it has a route to the destination, and therefore it causes the broadcast storm problem. This paper proposes an optimistic approach OpSOA to mitigate the broadcasting storm problem and to scale back the communication overheads of routing protocols by forming sectors within the network and finding the route to destination by two sectors at a time. The simulation result shows that the proposed mechanism substantially reduces route requests. Since the proposed protocol searches for the destination sector wise thereby reducing network wide broadcast of routing requests, traffic, collision and contention. There by there can be an increase in the packet delivery ratio and decrease in the average end-to-end delay

1. International Journal of Computer Engineering and Technology (IJCET), ISSN 0976-6367(Print),
ISSN 0976 - 6375(Online), Volume 5, Issue 8, August (2014), pp. 138-143 © IAEME
INTERNATIONAL JOURNAL OF COMPUTER ENGINEERING
TECHNOLOGY (IJCET)
ISSN 0976 – 6367(Print)
ISSN 0976 – 6375(Online)
Volume 5, Issue 8, August (2014), pp. 138-143
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IJCET
© I A E M E
AN OPTIMISTIC SECTOR ORIENTED APPROACH TO MITIGATE
BROADCAST STORM PROBLEM IN MANETS
N. Prathibha Bharathi
Student of M. Tech (CSE),
Department of CSE,
Dr.K.V.S.R.C.E. for Women, Kurnool, A.P., India
B. Mahesh
Associate Professor,
Dept of CSE,
Dr.K.V.S.R.C.E. for Women, Kurnool, A.P., India
138
ABSTRACT
In mobile ad hoc networks (MANETs), due to frequent changes in topology there exist more
link breakages which lead to high rate of path failures and route discoveries, which cause an
increased routing control overhead. Thus, it is necessary to reduce the overhead of route discovery in
the design of routing protocols for MANETs. In a route discovery, broadcasting may be an
elementary and effective data dissemination mechanism, wherever a mobile node blindly
rebroadcasts the first received route request packets unless it has a route to the destination, and
therefore it causes the broadcast storm problem. This paper proposes an optimistic approach OpSOA
to mitigate the broadcasting storm problem and to scale back the communication overheads of
routing protocols by forming sectors within the network and finding the route to destination by two
sectors at a time. The simulation result shows that the proposed mechanism substantially reduces
route requests. Since the proposed protocol searches for the destination sector wise thereby reducing
network wide broadcast of routing requests, traffic, collision and contention. There by there can be
an increase in the packet delivery ratio and decrease in the average end-to-end delay.
Keywords: MANETs; Route Discovery; Broadcasting; Broadcast Storm; Optimistic Approach;
Sectors.

2. International Journal of Computer Engineering and Technology (IJCET), ISSN 0976-6367(Print),
ISSN 0976 - 6375(Online), Volume 5, Issue 8, August (2014), pp. 138-143 © IAEME
139
1. INTRODUCTION
Mobile ad hoc networks (MANETs) consist of a collection of freely movable nodes which
communicates using wireless links and which do not require any fixed infrastructure [1]. MANETs
rely on the broadcasting capability or specialized flooding mechanism when performing route
discovery or gathering some global information [2], [3]. Broadcasting is the most frequently used
operation in MANETs for the dissemination of data and control messages in many applications. In
broadcasting when a node receives the message for the first time then it will forward the messages to
all other nodes connected in the network, message flooding, there arise a problem of redundant
transmission which results in packet collision. The broadcast redundancy significantly rise as the
average number of neighbors increases [4]. It is also difficult to reduce the number of forwarding
nodes in broadcasting. In Ad-hoc network, a packet collision occurs when two or more nodes try to
transmit a packet from corner to corner in the network at the same time. Packet collisions could end in
the loss of packet reliability or will slow down the performance of a network.
Once this redundancy will increase it ends up in severe network congestion and significant
performance degradation, which is referred to as the broadcast storm problem [5]. In broadcast-based
systems, we use message flooding to broadcast messages. There is no specific destination; thus each
neighbor node is contacted then forwards the message to its own neighbors till the message’s lifespan
expires.
Thus the main objective of broadcasting algorithms is to reduce the redundant transmissions.
The important aspect to achieve this is to limit the number of forwarding nodes. In MANETs, the
forwarding node set for broadcasting is generally selected in a localized manner, wherever each node
determines its own status of forwarding or non forwarding based on local information or the status of
a node is selected by its neighbors. A limited forwarding node set is considered to be more efficient
due to the reduced number of transmissions within the network. Therefore, to reduce the total number
of transmissions we use sectors of nodes within the network and we transmit the broadcast messages
two sectors at a time.
The remainder of this paper is organized as follows. Section II reviews the present
broadcasting mechanisms available in literature. Section III describes the proposed OpSOA approach.
In Section IV we evaluate the performance of our proposed approach. Section V concludes the paper
with an outlook to future research.
2. RELATED WORK
Broadcasting is an effective mechanism for route discovery but the routing overhead
associated with the dissemination of routing control packets such as RREQ packets can be large,
when the network density is high and the network topology frequently changes. One of the earliest
and the classical way of broadcasting in MANETs is flooding. But with blind flooding broadcast
storm occurs.
Traditional on-demand routing protocols [6, 7, 8] produce a large amount of routing control
traffic by blindly flooding the entire network with RREQ packets during route discovery. In
traditional AODV, an intermediate node rebroadcasts all RREQ packets that are received for the first
time. Assuming no intermediate node has a valid route to the destination and N is the total number of
nodes in the network, the number of possible rebroadcast in AODV is N −1. In the basic probabilistic
route discovery a source node sends an RREQ to its immediate neighbors with probability p =1. As an
intermediate node first receives this RREQ packet, with probability p 1, it rebroadcasts the packet to
its neighbors and with forwarding probability 1 − p it simply drop the packet. As the decision to
rebroadcast a packet of each node is independent, the possible number of rebroadcasts is p x (N −1).
This is referred as Fixed Probabilistic Route Discovery (FPR) [9].

3. International Journal of Computer Engineering and Technology (IJCET), ISSN 0976-6367(Print),
ISSN 0976 - 6375(Online), Volume 5, Issue 8, August (2014), pp. 138-143 © IAEME
In a network of random distribution of mobile nodes like MANETs, there are regions of
varying degrees of node density. Thus the need for an appropriate adjustment of the forwarding
probability arises. Therefore, FPR suffers from unfair distribution of forwarding probability; since
every node is assigned the same value regardless of their local topological characteristics. It is critical
to identify and categorize mobile nodes in the various regions of the network and appropriately adjust
their forwarding probabilities.
To overcome the disadvantages of FPR the authors in [9] proposed a generic probabilistic
route discovery algorithm (DPR) that dynamically determines the forwarding probability of an RREQ
taking into consideration the set of covered neighbors and the local density of the forwarding node.
This scheme only considers the coverage ratio by the previous node, and neglects those neighbors
which receive the duplicate RREQ packet. Thus, it needs further optimization and extension. Authors
in [10] proposed an approach MobDHop-AODV to work on top of the stable, two-tier cluster
structure formed by the MobDHop clustering algorithm. The goal of this protocol is to exploit the
aggregated topology information stored at every cluster head to avoid the need to flood the network
with route request (RREQ) packets in the search for intended destinations.
In this paper, we propose an efficient optimistic sector oriented approach (OpSOA) to yield a
significant performance improvement in terms of reduced network wide route requests by limiting the
broadcasts to two sectors at a time. The proposed approach is simple enough for easy implementation.
The detail of the scheme is described in the next section.
140
3. PROPOSED WORK
A new approach namely Optimistic Sector Oriented Approach (OpSOA) is introduced in this
work. The goal of this approach is to reduce the number of network wide route request (RREQ)
packets by limiting them to two sectors at a time. By this approach the need to flood network wide
RREQ packets to search for intended destination is reduced. Note that GPS assistance is necessary in
the proposed algorithm.
As we know that, in broadcasting when a node receives the message for the first time then it
will forward the message to all other nodes connected in the network, message flooding, there arise a
problem of redundant transmission which results in packet collision. Packet collisions may also result
in the loss of packet reliability or can slow down the performance of a network. The broadcast
redundancy significantly rise as the average number of neighbors increases [4]. When this redundancy
increases it results in the severe network congestion and significant performance degradation, a fact
called the broadcast storm problem [5].
To avoid this broadcast storm problem; instead of forwarding the received messages to all
other nodes in the network, we forward the broadcast messages two sectors at a time only. Therefore,
by reducing the total number of broadcast transmission through the sector approach broadcast storm
problem can be alleviated. In the proposed mechanism smart antenna systems that form directional
transmission/reception beams switched beam and steerable beam are used [11].
3.1 IMPLEMENTATION
In the proposed approach, the source node divides its neighbors into eight sectors and informs
its neighboring nodes about the sectoring information.

4. International Journal of Computer Engineering and Technology (IJCET), ISSN 0976-6367(Print),
ISSN 0976 - 6375(Online), Volume 5, Issue 8, August (2014), pp. 138-143 © IAEME
Figure 1: MANET divided in to sectors
The source node first chooses two sectors which are opposite to one another say 0 and 4 and
initiates a sector-wide broadcast of RREQ message to search for the route to destination node. Since
each node in the network are aware of their position and its sector information, nodes in a given sector
only broadcasts the message to the nodes within the sector only. If the destination node is found in the
clusters 0 or 4, then there is no need to broadcast the messages in the entire network. Otherwise, the
source node will initiate the request to two more clusters say 1 and 5. This process continues until the
destination is found or all sectors are completed.

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9. ()
Figure 2. Pseudocode for OpSOA.
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By this we will reduce the number of network wide RREQ messages initiated by the source
node. The possibility of having broadcast storms can be reduced and the limited resources such as
channel resources and device resources in MANETs can be preserved. By reducing the control traffic,
more data traffic can be transmitted over the network.
141

10. International Journal of Computer Engineering and Technology (IJCET), ISSN 0976-6367(Print),
ISSN 0976 - 6375(Online), Volume 5, Issue 8, August (2014), pp. 138-143 © IAEME
142
4. PERFORMANCE EVALUATION
In order to evaluate the performance of the proposed mechanism, we compare it with some
other mechanism using the NS-2 simulator. We compare our approach with MobDHop-AODV [10],
which is an optimization scheme with a cluster approach for reducing the overhead of RREQ packet
incurred in route discovery in the recent literature. We evaluate the performance of routing protocols
using the metric “Number of RREQ Transmitted” i.e., total number of RREQ messages transmitted by
the source and intermediate nodes.
Figure 3: Total number of RREQs transmitted.
Figure 3 show that OpSOA successfully reduced the total number of network-wide RREQ
messages. This is attributed to the fact that OpSOA avoids transmission of network wide RREQs by
transmitting them sector wise. If the destination is located inside the first or second or third set of
searched sectors unnecessary network-wide flooding of RREQ messages can be avoided.
5. CONCLUSION
In this paper, we have proposed, simulated and evaluated a new mechanism for optimizing
broadcasting in MANETs. MANET routing protocols rely largely on a broadcast-based route
discovery mechanism whereby route request messages are flooded across the entire network in search
of routes to destination. This approach does not have a significant impact on small networks but as the
network size grows, the communication overheads leading to a broadcast storm, which consume a
large portion of the shared wireless bandwidth, leaving little for the actual data traffic. Among the
many proposals addressing the scalability problem, sectoring has been identified as a good candidate,
which can limit network-wide flooding of routing requests. Sector setup and management requires
periodical exchange of control messages among nodes. However, if managed properly, substantial
reductions in routing control overhead can be achieved.
Through simulations we showed that there is a substantial reduction in route request messages
by limiting network-wide broadcast of route discovery messages. However, once node movement is
very frequent, the delivery ratio of the proposed approach is going to be smaller, which we consider in
the future works.

11. International Journal of Computer Engineering and Technology (IJCET), ISSN 0976-6367(Print),
ISSN 0976 - 6375(Online), Volume 5, Issue 8, August (2014), pp. 138-143 © IAEME
143
ACKNOWLEDGMENT
The authors wish to acknowledge K. Karthik, K. Kishore Kumar and A. Bhanutheja for their
work, useful feedback, and comments during the preparation of this paper.
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