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Ad hoc network is a collection of mobile hosts which is self organized, self
maintained network. It dynamically forms a wireless network without any
backbone infrastructure and centralized administration. Due to the lack of fixed
infrastructure the control overhead increases in the network. The aim of the
paper is to reduce the control overhead by using the domination set based
routing. The nodes which use to connect all the other nodes in the network are
called dominating nodes, and the set of dominating nodes creates domination
set. This paper proposes a new approach for finding the route and reducing the
reroute establishment delay and increasing the packet delivery ratio. The
efficiency of the method is demonstrated through simulation study using NS2.



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The evolution of mobile ad hoc networks
(MANET) is growing rapidly. The nodes in the MANET are self sufficient and each
node is act as either router or source. There is no central controller in MANET
and the control is distributed among the nodes. Topology of the network is
dynamic and the topology change is more frequent. Conventional routing
algorithms are not suitable for MANET. There are many routing algorithms
proposed for MANET timely. Mainly the routing algorithms are categorized into
two i.e. proactive and reactive 7. Proactive algorithms are the extension of
wired routing protocols. In proactive routing algorithm all the nodes keep the
routing information in the routing table at the time of network initialization.
All nodes exchange this information periodically with neighbors, which causes very
high routing overhead. In the reactive routing protocol, the route is decided
only when a node wants to send some data. In this case, there is some delay
occurs for route establishment since the routing information is not readily
available; many control packets are used for finding the route. The control packet
also brings routing overhead in the network. As per study, it has been reported
that the reactive algorithms are more efficient than proactive ones 7. The
main constraints in MANET include high mobility, low bandwidth and low energy.
Due to the high mobility, frequent disconnections are more in MANET. In all
reactive algorithms, when the route is broken then the route re-establishment
process reduce the performance of the network by inducing more overhead.

This paper proposes a method to reduce
the reroute establishment delay and routing overhead by using the dominating
nodes in the network. Based on the study of Domination Based Routing, compared
the performance with all other well known algorithms, This clearly justifies
that the proposed work is more efficient in terms of packet delivery ratio,
control overhead and packet drop. In this method, initially all the dominating
nodes in the networks are identified. From this a domination set is created. A
set is a dominating set, if all the nodes in the network are either in the set
or the neighbors of the nodes in the set 2. The route is established through
the nodes in the domination set only. All nodes in the network can be reached
through the dominating nodes. When the route fails, it is easy to find the new
route by using the domination nodes. This ensures the re-route establishment
without any delay and overhead, thereby enhancing the routing performance, even
when the route breaks occurs.

The paper is structured as follows.
Section 2 gives the brief idea about how the domination set is calculated.
Section 3 describes the proposed domination based routing. Simulation study and
results is presented in Section 4 and the conclusion is given in section 5.


calculation of Domination Set

Let G = (V;E) be a connected,
undirected, simple graph here V is the vertex set and E is the edge set. A set of vertices S in a graph
G is a dominating set if every vertex not in S is adjacent to at least
one vertex in S. The minimum number of vertices which dominates the graph G is
called minimum dominating set. A set
of vertices S is independent if
no two vertices in S are adjacent. A
connected dominating set (CDS) is a subset S of a graph G
such that S forms a dominating set and S is connected 1, 2.

Every node (vertex) in the network can
be reached through the domination nodes. An example of mobile ad hoc network is
shown in Fig. 1 and Fig. 2. with domination nodes N4, N7 and N9. There are
multiple minimum dominating set but the number of nodes in the set must be the
same in domination set. For same network Fig.1 and Fig. 2 shows two different
domination set.


















Fig. 1 A typical Mobile Ad hoc Network with
domination node {N4,N7,N9}
















Fig. 2 A typical Mobile Ad hoc Network with
domination node {N4,N7,N10}


for finding domination set

The algorithm given below creates the
domination set by calculating the adjacency matrix and collecting the nodes
corresponding to the maximum connected node, from the row sum.



(b is a neighbour)


to neighbour list

this list to its neighbours


(a is a neighbour of b)                                 //Find
adjacency matrix






each row in adjacency matrix                   //calculate
the domination matrix


the row sum in adjacency matrix

the node with maximum degree

this to ” d set”

any node is not connected to the nodes in the d set then add this also to the d










Route discovery through dominating nodes

Domination Set Based Routing

The given algorithm first finds the
domination set. Then the path is established to the destination only through
the domination nodes. The nodes in the domination set connect all the nodes in
the network quickly. So it is easy to get the destination within a very short interval. Whenever
the route failure occurs then the corresponding domination node identifies the
problem and fixes it locally. It can reach the destination through other nodes
if possible. Otherwise it will flood the route failure report to the other
domination nodes. In the initial phase, the domination nodes are determined
form the adjacency matrix. For that each node determines its neighbour node by
sending the HELLO packet. After determining the neighbours, the neighbouring
list is sent to the adjacent nodes and each node prepares the adjacency matrix.
From this matrix, it is easy to find out the dominating nodes and finally
domination set by using the above mentioned algorithm.

In Fig. 3. the domination set is {N4, N7,
N9}. N1 is the source and N11 is the destination nodes. N11 can be reached from
N1 through N4, N7 and N9. In the initial route discovery process each node
tries to connect the domination node from the source node. The route to
destination is always through the dominating nodes even if the shortest link
exists. In the initial stage, the cost of establishing the route is higher than
the other routing algorithms; but this is very useful in the dynamic networks,
because mobile ad hoc network is highly dynamic in nature. So this is helpful
for finding the alternate route easily. In the given example if link N10-N11 is
broken, then need not to worry about the link because still we reach all the
nodes easily. Suppose we have domination set {N4,N7,N11} In fig. 3 if the link N10-N11
is broken in fig. 2 then the node N9 can easily set up the connection  N9-N11 to the destination.


The performance evaluation of
the proposed algorithm has been done
by using simulation tool NS2.The performance of DBR is
compared with the existing algorithms AODV and DSR. The metrics used for performance analysis
were packet delivery ratio, number of packets dropped and the routing
overhead It has been observed that DBR perform better than AODV and DSR. The
simulation parameters are listed in the Table. 1

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