1
Reducing Overhead in Manet Using Lightweight Proactive Source Routing
Protocol
1
A.Arthi Bala, 2Dr.S.Matilda
M.E Student of IFET College of Engineering, Villupuram , TN-India, arthi_bal @yahoo.co.in
2
Professor, CSE Dept, IFET College of Engineering , Villupuram, TN-India
1

Index
Abstract-- Routing and Data forwarding are the two most
opportunistic data forwarding, proactive routing, routing
Terms
--
Mobile
ad-hoc
network(MANETs),
important operations performed at the network layer.
Due to the lack of an efficient proactive routing scheme
with strong source routing capability, opportunistic data
overhead control, source routing, breadth first search spanning
tree(BFST), differential update, tree-based routing.
forwarding was not generally utilized in MANETs. A
I. INTRODUCTION
lightweight proactive source routing (PSR) protocol was
The Source routing enables a sender of a packet to
introduced to achieve opportunistic data forwarding. In
partially or completely determine the route through which
this paper, we enhance the lightweight PSR to further
the packet is sent to the destination. In source routing, the
reduce the routing overhead in MANET and achieve
route used will tend to be relatively static and therefore
better network performance. Our enhanced proactive
cannot optimize use of communication facilities as well as
source routing protocol is a source routing protocol that
the potentially more dynamic hop-by-hop route selection
facilitate opportunistic data forwarding. In PSR, each
system. The protocols that support source routing are mostly
node maintains a entire network topology information as
not proactive in nature. In networks utilizing a proactive
a breadth-first search spanning tree. This information is
routing protocol, every node preserves one or more tables
periodically exchanged among neighboring nodes for
representing the entire network topology. These tables are
updated network topology information. Thus, PSR
updated regularly in order to maintain a up-to-date routing
enable a node to have detailed path information to reach
information from each node to every other node. The nodes
all other nodes in the network. In PSR, for every 2
in the network need to exchange the network topology
cycles, the differential update message is broadcast by
information to keep the up-to-date routing information. So
each node for reducing routing overhead. Although it
this leads to relatively high overhead on the network.
maintains more network topology information, it has
Opportunistic data forwarding represents a hopeful
much smaller overhead than optimized link state
solution to utilize the broadcast nature of wireless
routing(OLSR)
On-Demand
communication links [9]. Opportunistic data forwarding
Distance Vector(AODV) Protocol. It also has much less
refers to a way in which data packets are handled in a
overhead than reactive source routing such as dynamic
multihop wireless network. AODV, DSDV, and other DV-
source routing. Our tests using computer simulation in
based
OPNET indicate that the overhead in PSR is only a
opportunistic data forwarding since they were not designed
fraction of the overhead of these baseline protocols.
for source routing.
protocol and Ad-Hoc
routing
algorithms
are
not
appropriate
for
Every node in these protocols only
knows the next hop to reach a given destination node but not
the complete path. OLSR and other LS-based routing
protocols could support source routing, but their overhead is
still fairly high for the load-sensitive MANETs. DSR and its
2
derivations have a long bootstrap delay and are therefore not
its relevant information from the topology repository
effective for frequent data exchange, particularly when there
maintained by the detecting node.
are a large number of data sources[1].So there is a need for a
Before describing the details of PSR, we will first review
efficient
some graph-theoretic terms used here. Let us model the
proactive
routing
protocol
that
supports
opportunistic data forwarding with strong source routing.
In this paper, we enhance a lightweight proactive source
routing
(PSR)
protocol
to
ease
opportunistic
network as undirected graph G = (V, E), where V is the set
of nodes (or vertices) in the network, and E is the set of
data
wireless links (or edges). Two nodes u and v are connected
forwarding in MANETs. In PSR, each node maintains an
by edge e = (u, v) ∈ E if they are close to each other and can
entire network topology information in a breadth-first search
directly communicate with given reliability. Given node v,
spanning tree (BFST) structure. This information is
we use N(v) to denote its open neighborhood, i.e., {u ∈ V
periodically exchanged among neighboring nodes for
|(u, v) ∈ E}. Similarly, we use N[v] to denote its closed
updated network topology information that enables a node to
neighborhood, i.e., N(v) ∪ {v}[11].
have full-path information to all other nodes in the network.
A. Constructing Breadth-first spanning tree
This allows it to support both source routing and
After the data transmission is initiated, the node starts to
conventional IP forwarding[1]. Since the information is
construct breadth-first spanning tree. At the beginning, node
maintained in a tree structure, routing information updation
is only aware of the existence of itself; therefore, there is
is easily performed. When doing this, we try to reduce the
only a single node in its BFST, which is root node. In the
routing overhead of PSR as much as we can. Our simulation
very first iteration, by exchanging the BFSTs with the
results indicate that PSR has only a fraction of overhead of
neighbors, it is able to construct a BFST within N[v], i.e.,
OLSR, AODV, and DSR
the star graph centered at v, which is denoted Sv. In each
subsequent iteration, nodes exchange their spanning trees
The remainder of this paper is organized as follows.
Section II describes the design and implementation details of
our enhanced routing scheme. The computer simulation,
related experiment settings, and comparisons between PSR
and existing protocols are presented in Section III. Section
IV concludes this paper with a discussion of future research.
II. DESIGN OF ENHANCED LIGHTWEIGHT PSR
with their neighbors.
Consider a node v has received the BFSTs from some of its
neighbors. Including those from whom v has received
updates in recent previous iterations, node v has a BFST,
which is denoted Tu, cached for each neighbor u∈N(v).
Node v constructs a union graph, i.e.,
GV  SV U
 (T
u
uN ( v )
Essentially, PSR provides every node with a breadth-first
spanning tree (BFST) of the entire network rooted at itself.
To do that, nodes once in a while broadcast the tree structure
 x)
------------- (1)
we use T − x to denote the operation of removing the subtree
of T rooted at node x.
to their best knowledge in each iteration. Based on the
topology information collected from neighbors during the
most recent iteration, a node can expand and refresh its
knowledge about the network topology by constructing a
deeper and more recent BFST. On the other hand, when a
neighbor is deemed lost, a procedure is triggered to remove
Fig. 1. Example of a MANET.
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• Data packets or routing updates has not been received
from this neighbor for a specific period of time.
• A data transmission to node u has failed, as reported
by the link layer.
• Node v responds by:
i. First, updating N(v) with N(v) − {u};
ii. Constructing the union graph with the information
Fig. 2. Union graph constructed at node A
After certain no of iterations of operation, each node in
of u removed, i.e.,
GV  SV U
(T
W
 u)
WN ( v )
the network has constructed a BFST of the entire network
-----------------(2)
since nodes are timer driven and, thus,
iii.Finally, computing BFST Tv.
synchronized. This information can be used for any source
C. Rationalized differential update
rooted at itself
routing protocol.
After the BFST is constructed, each node starts to
The figure.2 shows the union graph constructed at node A
broadcast the full tree structure in a full-dump message once
receiving BFST from their neighbors after four iterations.
very few cycles. In every 2 cycles, a node broadcasts a
Performing breadth first search on the union graph
produce the Breath first search spanning tree(BFST).
differential update message to depict the topology changes
in its locally stored BFST if any.
1) Compact tree representation
For the full-dump messages, the BFST information
stored at a node is broadcast to its neighbors in a short
packet. First, general rooted tree is converted into a binary
tree of the same size, e.g., t nodes, using left-child sibling
representation. Then, binary tree is serialized using a bit
sequence of 34 × t bits, assuming that Internet protocol v4 is
used. Specifically, the binary tree is scanned layer by layer.
Fig. 3. Breadth first search spanning tree
Figure.3 shows the breadth first search spanning tree
constructed at node A.
B. Neighborhood trimming
When a neighbor mobile node moves out the transmission
range, its contribution to the network connectivity should be
removed; the part of the BFST representing the information
about that neighbor has to be removed. This process is said
Fig. 4. Binary tree
to be neighbor trimming. Consider node v. The neighbor
When processing a node, IP address is included in the
trimming procedure is invoked at node v about neighbor u
sequence. Two bits are used to indicate if it has the left
either by the following cases
and/or right child. For example, the binary tree in Fig.4.is
4
represented as A10B11D11C00F00E10G01H01I00. As
Then, it incorporates the edges of Tu for a new BFST. Note
such, the size of the update message is a bit over half
that the BFST of (Tv− u) Tu may not contain all necessary
compared with the traditional approach.
edges for v to reach every other node. Therefore, it is still
needed to construct union graph
(Tv− u) 
 (T
W
WN ( v )
 v)
-----------------(3)
III. PERFORMANCE EVALUATION
We study the performance of PSR using computer
simulation with OPNET version 14.5. We compare PSR
Fig. 5. PSR Packet format
The PSR packet header is similar to OLSR packet
against OLSR [7], AODV [9], and DSR [8], which are three
fundamentally different routing protocols in MANETs, with
header. PSR perform link recognizing and neighborhood
varying network densities and node mobility rates.
detection periodically.so the PSR packet header is designed
A. Experiment settings
as in the OLSR. For the sake of reducing the packet size, the
The network topology with 40 nodes is generated
IP address of all the nodes connected in the network is
according to the given inputs in the simulation, such the
included in the Network topology tree field. The Left-right
number of nodes in the network, the depth of the network,
child relation field holds the left-right relation of each node.
the bandwidth of the links in the network, and the
The binary tree is constructed by taking the IP addresses and
transmission range. In modeling node mobility of the
values present in these two fields. The network topology tree
simulated MANETs, we use the random waypoint model to
field and the left-right relation field both together represent
generate node trajectories. In this model, each node moves
the entire topology information.
toward a series of target positions.
When the node receives the routing updates, it converts
the bit sequence into binary tree. Then the binary tree will be
converted into general rooted BFST.
2) Stable BFST
The differential update message contains a part of the
BFST that reflects the changes in the network topology. The
size of a differential update is determined by how many
edges it includes. Since there can be a large number of
BFSTs rooted at a given node of the same graph, it is need
to modify the BFST maintained by a node as little as
possible when changes are detected. To do that, a small
portion of the tree needs to change either when a neighbor is
lost or when it reports a new tree.
Fig.6. Network with 40 nodes created in Opnet
simulator
Four scenario are created in OPNET simulator to evaluate
the performance of the AODV,OLSR, DSR and PSR
Consider node v and its BFST Tv. When it receives an
protocols. In the first scenario, DSR is used as a mobile ad-
updated routing information from neighbor u, which is
hoc routing protocol. Trajectories are defined for nine
denoted Tu, it first removes the subtree of T v rooted at u.
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nodes. In the second scenario, AODV is used as a mobile
ad-hoc routing protocol. In the third scenario, the OLSR is
used as a mobile ad-hoc routing protocol. In the last
scenario, the PSR is used as a mobile ad-hoc routing
protocol.
Fig. 9. Routing Traffic sent(bits/sec)
The
fig.9 indicates that PSR sent approximately 2000
bits/sec.It indicates that PSR has low routing overhead than
AODV,DSR and OLSR
IV. CONCLUSION
The PSR provides more topology information than Distance
vector protocol. As PSR does not use the flooding
mechanism, it prevents the unnecessary retransmission. PSR
Fig.7. Selecting PSR as a AD-HOC routing protocol
Figure. 7 shows that PSR is selected as a AD-HOC routing
protocol in the PSR scenario.
uses only one type of message named Hello_NT message,
both to exchange routing information and as hello beacon
messages which is needed to detect neighbors and link
sensing. Rather than packaging a set of discrete tree edges in
the routing messages, a converted binary tree is packaged to
reduce the size of the payload by about a half. Full-dump
messages and differential updates are interleaved to maintain
the network stability. As PSR maintains the routing
information as a tree structure, whenever a network topology
is changed, the routing information will be quickly updated .
The TCP throughput, end-to-end delay and routing overhead
in bytes per node per second are evaluated for all the four
protocols. The routing overhead of PSR is only a fraction or
less compared with AODV, OLSR, and DSR, as evidenced
by our experiments. Yet, it still has similar or better
performance in transporting TCP and UDP data flows in
Fig.8. Setting PSR parameters in OPNET simulator
mobile networks of different velocity rates and densities.
Figure. 8 shows that PSR parameters Hello_NT
Interval, Neighbor Hold time, Topology hold time,
Duplicate Message Hold time and addressing mode are
assigned a value 2.0,6.0,15,30 and IPv4 respectively.
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