17-06-2013, 04:15 PM
Comparative Performance Evaluation of Routing Algorithms in IEEE 802.11 Ad Hoc Networks
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Abstract
In this paper we examine the behavior of Ad Hoc networks
through simulations, using different routing protocols and
various topologies. We examine the difference in performance,
using CBR application, with packets of different size through a
variety of topologies, showing the impact node placement has on
networks performance. We show that the choice of routing
protocol plays an important role on network’s performance. We
also quantify node mobility effects, by looking into both static
and fully mobile configurations. Our paper presents a systematic
analysis of a variety of different ad hoc network topologies in
terms of node placement, node mobility and routing protocols
through several simulated scenarios.
Introduction
Ad Hoc networks’ advantage is the promise of
infrastructure – free communication. In an Ad hoc network
configuration, nodes need to cooperate with each other in
establishing transmission paths through the network, using
the limited capacity and available resources the best
possible way.
Network topology can change rapidly when nodes move in
a wireless environment. Therefore, it is very likely that
packets must be forwarded through different paths/routes
every time. Ad hoc routing protocols are used to discover
routes between source and destination nodes. They belong
in three categories, proactive, reactive and hybrid. In
proactive routing protocols [1], nodes maintain routing
information to every other node of the network, which is
stored in routing tables, which are periodically updated
when topology changes. In our simulations we have used
DBF (Distributed Bellman Ford), however there are
several proactive routing protocols, such as DSDV, GSR,
OLSR [1] et.al.
Fixed Topology Networks
Simulations on Chains of Nodes
For our simulations, we have used the Qualnet Simulator
[9]. Our first scenario involves chains of nodes, whose
length increases in each simulation. Nodes are static, using
IEEE 802.11b and DBF as routing protocol. Node 1 is the
source node, transmitting at 2Mbps with a constant bit rate.
The last node of the chain is the destination node (node 6
in Fig. 1), and the intermediate nodes are used only to
forward packets.
Simulations in Lattice Networks
In this section we examine two different topologies, both
consisting of 18 nodes with a 200m distance between
them. The difference between the two scenarios is node
placement. In the first case, nodes are placed in three
chains consisting of six nodes, whereas in the second
configuration we use six chains with three nodes each. The
rest of the simulation parameters are the same as in section
2.2.Average per flow throughput values are shown in fig 8.
Lattice Networks with Limited Mobility
3 In order to examine node mobility effects, in this section
we present simulation results on two different topologies.
In both cases, we assume a lattice network of 36 users,
similar to the one in fig.4, distributed in a 1000x1000m
area where nodes have 100m distance from their
neighbors. The left and right columns of nodes in this
network are static, serving as source and destination nodes,
respectively. We simulated two different scenarios. In the
first one, apart from the static nodes at the edges, there is
another static column of nodes, which is the 4th from the
left. In the second scenario, the two columns in the middle
of the network (3rd and 4th) are static.
Random Topology Networks
In this section, we introduce full node mobility
and look into the comparative performance of the three
routing algorithms in a random topology 11Mbps IEEE
802.11b Ad Hoc network. Simulation area is 1000x1000m
and the network consists of 30 users. The network operates
in 802.11 Distributed Coordination Function CSMA/CA
mode as before. We simulate CBR applications with the
same parameters as in section 3 with flows’ destinations
chosen randomly from a uniform distribution. Simulation
time is 600 sec. We use a RWP mobility model, with a
maximum speed of 10m/s and 30sec pause time.
We simulate two different scenarios. In the first, each node
acts exclusively either as a sender or a receiver of packets,
therefore there are 15 active CBR flows. In the second
scenario there are 30 CBR flows since a node functions
both as sender and receiver of packets whereas in both
scenarios every node can act as a relay node. We use three
different routing protocols, DBF, DSR and ZRP in each
scenario and packets of 64, 500 and 1500 bytes long as in
section 3. Nodes send with a rate of 40packets/sec. The
results in fig. 11 and 12 pertain to throughput and average
delay respectively, for both scenarios.
Conclusions
Our focus in this paper is to evaluate the performance of
an Ad Hoc network, in scenarios involving both static and
mobile nodes, using different routing protocols and offered
load conditions. We compare three different routing
protocols, each representing one of the three types of
routing protocols, i.e., proactive, reactive and hybrid. Our
main contribution (relative to previous work) is the
systematic analysis of these routing protocols in a variety
of network topologies including static nodes scenarios,
scenarios with limited node mobility and full node
mobility (sections 2, 3, 4 respectively), citing a simple
throughput theoretical analysis for each of those
topologies.