Proceedings of 2011 International Conference on Signal Processing, Communication, Computing and Networking Technologies (ICSCCN 2011)
A Study on The Effect of Traffic Patterns on
Routing protocols in Ad-hoc Network Following
RPGM Mobility Model
Arindrajit Pal∗ , Jyoti Prakash Singh† , Paramartha Dutta‡ , Paulomi Basu† and Doyel Basu†
∗ Dept.
of Computer Science and Engineering,
Academy of Technology, West Bengal, India
Email: arindrajit@gmail.com
† Dept. of Information Technology,
Academy of Technology, West Bengal, India,
Email: jyotip.singh@gmail.com
‡ Department of Computer and System Sciences,
Visva-Bharati University, West Bengal, India,
Email: paramartha.dutta@gmail.com
Abstract—Mobile Ad-hoc networks(MANET)s are self organizing networks which can form a communication network without
any fixed infrastructure. The constant bit rate (CBR) traffic
is very well known traffic model for mobile Ad-hoc network.
CBR traffic generates data packets at a constant rate. This
constant rate packet generational is good enough for text data
packets. The multimedia applications generally generate packets
which sometimes increase and might be sometimes followed by
some idle period. CBR traffic model does not accommodate the
specific features of multimedia data. The day by day increase
of multimedia data prompts us to investigate some other traffic
models which can accommodate the specific features of these
data. One such traffic model is Exponential traffic model which
is based on exponential distribution. The other model is Pareto
traffic model based on Pareto distribution. In this article, we have
tried to study the behavior of mobile Ad-hoc network routing
protocols under Exponential and Pareto traffic sources for nodes
moving with Reference Point Group Mobility model (RPGM). To
the best of our knowledge, this is the first attempt to analyze the
effect of traffic patterns with Reference Point Group Mobility
(RPGM) model on mobile ad hoc network routing. We have
chosen the Normalized routing load, Packet Delivery Fraction
and throughput as our figures of merit to compare various
protocols. We found high Normalized Routing Load for both
Exponential and Pareto traffic compared to CBR traffic in both
Dynamic Source Routing (DSR) and Ad hoc On-demand Distance
Vector protocol. The Packet Delivery Fraction is comparable in
all types of traffic patterns and routing protocols. Throughput
is high for Ad hoc On-demand Distance Vector (AODV) routing
protocol across all traffic models.
I. I NTRODUCTION
Ad hoc network is a infrastructure-less wireless network. A
source node communicates with a destination node directly
if the destination is within the transmission range of the
source otherwise source uses other intermediate nodes between
source and destination as relay nodes. The ad hoc network is
a multihop network without any centralized control. Hence,
the routing and the resource management are done through
different nodes in distributed manner. The physical movement
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of nodes leads to breakup of communication links between
adjacent nodes which leads to a number of control packet
transmission to announce these topology updates. The statistical behaviour of physical movement of nodes are captured by
different mobility models like Random Way Point (RWP)[2],
[10], [18], [17], Manhattan Grid (MGM)[6], Reference Point
Group Mobility Model (RPGM) [7], [19] etc.. Camp et al.
[3] have provided a good survey of the most frequently used
mobility models. The routing protocols in Ad-hoc network
can be grouped into two main categories based on the route
maintenance technique. They are (i) Proactive routing protocol
and (ii) Reactive routing protocol. A route between each
pair of nodes is maintained in proactive routing protocols
regardless of whether those routes are really being used or
not. In network, where proactive routing algorithm is used,
each node has got a complete picture of connectivity of all
nodes in the network. To keep this connectivity information,
each node maintains a table of information containing the
minimum number of hops and the next hop in the direction
of a specific destination. This table is kept up to date by
broadcasting all topology updates immediately or with a small
time shift to all other nodes in the network. So, proactive
routing algorithms are also known as table driven algorithm.
In proactive routing algorithm every node has a route to
destination always available. It does not have to incur any
delay for route discovery when a traffic source begins a
session with a remote destination. For a given link cost, the
nodes maintain and keep an optimal routes to all other nodes
of the network. A very popular and early proactive routing
protocols is Destination-Sequenced Distance-Vector (DSDV)
proposed by Perkins [15] in 1994. Like other table driven
routing algorithms it maintains several routing tables which
provide information about every possible destination within
the network. The tables contain the sequence numbers for
every destination along with the minimum number of hops
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Proceedings of 2011 International Conference on Signal Processing, Communication, Computing and Networking Technologies (ICSCCN 2011)
and the next hop in direction of a specific destination. However, due to high overheads and somewhat poor convergence
behavior, this protocol is not directly suitable for mobile ad
hoc networks. In a network using reactive routing algorithm,
nodes find and maintain the route which are really needed.
The nodes do not keep the complete knowledge of the network
topology. Whenever a path to destination is needed, a route
is searched and established. So, such a routing algorithm is
also known as on demand routing algorithm. The Ad hoc
On-demand Distance Vector (AODV) proposed by Perkins
[16] in 1997 is a popular example of on-demand routing
protocol. AODV uses traditional routing tables, one entry per
destination. Dynamic Source Routing (DSR) [9] is another
example of reactive routing which stores the complete hopby-hop route to the destination. The major difference between
AODV and DSR is that DSR uses source routing in which a
data packet carries the complete path to be traversed. On the
contrary in AODV, the source node and the intermediate nodes
store the next-hop information corresponding to each flow for
data packet transmission. All popular routing protocols for
MANET considers the constant bit rate traffic as the traffic
source. The traffic patterns play an important role in so far as
the performance of a routing protocol is concerned. The traffic
pattern changes with the nature of applications. Traditional
data applications generate constant bit rate traffic which is
the traffic model of choice of most of the researchers for a
long time in the area of mobile ad hoc network. Recently
multimedia applications have drawn the attention of a lot
of researchers in mobile ad hoc network. These multimedia
applications have a radically different traffic patterns. The data
rate in voice application increases till it reaches a maximum
peak. It is followed over an ideal period. This pattern of traffic
can be captured by Exponential or Pareto traffic. The rest of
this paper is organized as follows. Section 2 includes the Reference point group mobility model(RPGM). Section 3 contains
a brief introduction to different traffic patterns. In section 4,
we describe two popular reactive routing protocols. Section
5 contains the simulation settings and results. We conclude
the article in section 6 with some suggestions regarding future
directions.
II. R EFERENCE POINT GROUP MOBILITY MODEL (RPGM)
The real applications where Reference point group mobility
model(RPGM) model can be used properly is the mobility
behavior of the soldiers moving together in a group in the
battle field. There is a logical center or group leader in
each group. The movement of the group leader determines
the mobility behavior of all other members in the group.
Initially, each member of the group is uniformly distributed in
the neighborhood of the group leader. At every time instant,
each node has its own speed and movement direction is
derived by randomly deviating from that of the group leader.
This model realizes the spatial dependency of each node of
a group with logical center [12][5]. The movement of the
�
group leader at time t can be represented by motion ������
. Not only does it define the motion of the group leader
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itself, but also it provides the general motion trend of the
whole group. Each member of this group deviates from this
�
by some degree. The motion vector
general motion ������
�
������ can be randomly chosen or carefully designed based
on certain predefined paths. The movement of group members
is significantly affected by the movement of the group leader.
For each node, mobility is assigned to a reference point that
follows the group movement. Upon this predefined reference
point, each mobile node could be randomly placed in the
neighbourhood. Formally, the motion vector of group member
i at time t, ��� , can be described as,
�
+ � × ���
��� = ������
(1)
where the motion vector �.��� is a random vector deviated
by group member � from its own reference point.
III. T RAFFIC MODELS IN MANET
A. Constant Bit Rate (CBR)
The most popular traffic source in network simulation is
Constant Bit Rate (CBR) traffic. In case of CBR traffic
source, the data packets are generated at a constant rate with
parameters to change the inter packet interval. The CBR class
is commonly used for normal data transmission. In this traffic,
the data rate and the delay remain constant during the packet
transmission. The CBR traffic is not very useful for simulation
of real time multimedia traffic generated on demand and videoconferencing services [4][1].
B. Exponential Traffic
The exponential traffic model follows an ON/OFF packet
generation pattern. During On period, the packets are generated following an exponential distribution. One can tune the
traffic generation pattern using three parameters specified in
this traffic generator. The first parameter denotes the rate at
which the traffic can be generated during ON period. The
second and third parameter denote the ON and OFF periods
respectively. The Exponential Traffic class is found to be quite
useful for real time multimedia, video and voice traffic[13],
[1].
C. Pareto traffic
The Pareto traffic model also follows an ON/OFF packet
generation pattern. During ON period, the packet generation
rate varies following Pareto distribution. The shape of the
Pareto distribution is tuned using its shape parameter. The
other parameters of the traffic generators are the rate at which
the traffic can be generated during ON period and the ON
and OFF periods respectively. The multimedia, video and
voice traffic sources can be simulated well using Pareto traffic
generator[13], [1] .
IV. ROUTING A LGORITHMS IN MANET
We have applied our simulation studies on two popular
demand routing protocol namely Ad hoc On-Demand Distance
Vector (AODV) and Dynamic source routing (DSR). For the
sake of completeness the principles of those routing algorithms
are given below.
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Proceedings of 2011 International Conference on Signal Processing, Communication, Computing and Networking Technologies (ICSCCN 2011)
A. Ad hoc On-Demand Distance Vector (AODV)
Ad hoc On-Demand Distance Vector (AODV) is an effective
example of reactive on-demand routing protocol. It uses ondemand approach for finding routes i.e. a route is established
only when it is requested by a source node for transmitting data
packets to the receivers and these routes are maintained until
they are in need by the source. In AODV, each node maintains
at most one route per destination. Being a single path protocol,
it has to invoke a new route discovery whenever the only
path from the source to the destination fails. When topology
changes frequently, route discovery needs to be initiated time
and again which can be very inefficient. AODV maintains
a destination sequence number generated by the receivers
and determines an up-to-date path to the destination. A node
updates its route information only if the destination sequence
number of the current by received packet is greater than the
destination sequence number stored at the node. It indicates
the freshness of the route accepted by the source. To prevent
multiple broadcast of the same packet, AODV uses broadcast
identifier number that ensures loop freedom. This is because
the intermediate nodes only forward the first copy of the same
packet and discard the duplicate copies. When a route to a new
destination is needed, the node uses a broadcast route request
(RREQ) to find a route to the destination. Nodes that receive
the RREQ find out whether they are the destination or whether
they have a fresh route to the destination. Then they respond
to the RREQ by unicasting a route reply (RREP) back to the
source node [8]. A route can be determined when the request
reaches either the destination itself, or an intermediate node
with a fresh enough route to the destination. Since each node
receiving the request keeps track of a route back to the source
of the request, the RREP Reply can be unicast back from the
destination to the source, or from any intermediate node that
is able to satisfy the request back to the source. The figure 1
shows the route establishment of AODV routing protocol.
B. Dynamic source routing (DSR)
Dynamic source routing (DSR) is another example of reactive routing protocol. It generates the proper route only
when packet needs to be forwarded from source to destination.
Within the limit of the transmission range, the process of
finding a path is only executed when a path is needed by
a node. DSR makes aggressive use of source routing and
route caching. With source routing, complete path information
is available and routing loops can be easily detected and
eliminated without requiring any special mechanism. Because
route requests and replies are both source routed, the source
and destination, in addition to learning routes to each other,
can also learn and cache routes to all intermediate nodes. The
addresses of intermediate nodes in the route are kept within
the delivered packets. The route discovery process broadcasts
a ROUTE REQUEST packet that is flooded across the network in a controlled manner. ROUTE REQUEST packets
use sequence numbers to prevent duplication. The request
is answered by a ROUTE REPLY packet either from the
destination node or an intermediate node that has a cached
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[h]
Fig. 1.
Route establishment in AODV
route to the destination[6]. To take full advantage of route
caching, DSR replies to all requests reaching a destination
from a single request cycle. Thus, the source learns many
alternate routes to the destination, which will be useful in
case the primary route fails. The figure 2 shows the route
establishment of DSR protocol.
V. C OMPARISON BETWEEN AODV AND DSR
Both AODV and DSR are two on demand reactive routing
protocols. But these two routing protocols maintain the routes
in different way. AODV maintains the destination sequence
number and choices to RREQ floods. AODV uses a more
rigorous route-error notification mechanism and therefore has
access to more accurate routing information. In Figure 1, we
have shown that the path is 1-4-6. AODV has a concept of
route cache. If some intermediate node holds the path from
that node to the destination then AODV may established a
path from source node to that route cache. If we consider a
route node 2 holds cache route (5-6) then another path is 12-5-6. DSR is source routing protocol. It maintains multiple
routes to a destination and uses immoral mode listening. The
current specification for DSR does not contain any mechanism
for route entry invalidation. This leads to state cache entries,
predominantly at high mobility. In Figure 2, we have shown
the route establishment in DSR routing protocols. There are
three paths from source to destination like 1-4-6, 1-2-5-6, 13-6.
Fig. 2.
Route establishment in DSR
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Proceedings of 2011 International Conference on Signal Processing, Communication, Computing and Networking Technologies (ICSCCN 2011)
VI. S IMULATION RESULTS AND ANALYSIS
Our target in the experiment is to study the behavior of
routing protocol with different types of traffic sources under a
specific mobility scenario like Reference point group mobility
model(RPGM). We use Bonn-Motion [14] for generating
RPGM mobility scenarios. We generate four mobility patterns
with 30, 40 and 50 nodes moving in an area of 1000�×1000�
for a period of 1000 s with the first 3600 sec of each
mobility pattern ignored. It has been observed that with the
Reference point group mobility model(RPGM), nodes have a
higher probability of being near the center of the simulation
area, while they are initially uniformly distributed over the
simulation area initially. So, we skip 3600 s at the beginning
to mitigate the boundary effects of node movement simulation.
The cbrgen tool which is a part of ns-2 [11] distribution is
used to generate Constant Bit Rate traffic for 1000s with 1
packet/sec per source. The number of sources and destinations
were chosen randomly by cbrgen tool. Similar to cbrgen
tool we developed our own tool to generate Exponential and
Pareto traffic. The Exponential traffic source generates traffic
at 2 KB/s during ON period. The average ON and OFF
periods are 315 ms and 325 ms respectively. The Pareto
traffic source generates traffic at 2 KB/s during ON period.
The average ON and OFF periods are 315 ms and 325 ms
respectively. The source and destination are chosen randomly
in each traffic generator. We have used ns-2 [11] for network
simulation and traces are generated in new trace format. To
compare the performance of different routing protocols under
various traffic, we have used Normalized Routing Load, Packet
Delivery Fraction and Throughputs as out metric.
Fig. 3. Packet Delivery Fraction (%) in AODV and DSR for different traffic
models in RPGM
B. Normalized Routing Load
The Normalized Routing Load (NRL) denotes the measure
of control packets sent and forwarded by router to transmit
every byte of data packet. the Normalized Routing Load is
given by
�� ���� + �� � ���
× 100
(3)
��� =
���� ��� ���
where �� ���� and �� � ��� are the control packets sent and
forwarded by the router respectively and ���� ��� ��� is the
data packet received by the application. Figure 4 shows the
routing overhead in Normalized Routing Load. Normalized
A. Packet Delivery Fraction
Packet Delivery Fraction (PDF) is an important figure of
merit for Ad-hoc network routing protocols. Packet Delivery
Fraction is the ratio of the number of data packets successfully
delivered to the destinations to those generated by traffic
sources.
���� ��� ���
× 100;
(2)
� �� =
���� ��� ����
where ���� ��� ��� and ���� ��� ���� are the number of
data packets received and sent respectively by the application.
The Packet Delivery Fraction for CBR, Exponential and Pareto
traffic sources with AODV and DSR routing protocol is shown
graphically in Figure 3. From Figure 3, we observe that the
packet delivery fraction is very high for AODV and DSR
routing protocol in CBR traffic. For node 30, the Packet
delivery fraction is slightly low due to few number of nodes. In
Exponential and Pareto traffic environment in AODV routing
protocol, the Packet Delivery Fraction is very high for various
number of nodes. The Packet Delivery Fraction in DSR routing
for Exponential and Pareto traffic is average. We also observed
that if the number of nodes becomes higher then the Packet
Delivery Fraction is also high. From Figure 3 it is evident
that, the Packet Delivery Fraction increases for large number
of mobile nodes.
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Fig. 4. Normalized Routing Load(%) in AODV and DSR for different traffic
models in RPGM
Routing Load is the ratio of the number of control packets
propagated by every node in the network and the number
of data packets received by the destination nodes. In case of
DSR, each intermediate node records the number of packets
queued in control packet. The destination node uses this
information when selecting the route. Route breaks occur more
frequently in DSR because it often uses old routes. Hence,
more ROUTE ERROR packets are transmitted, and consequently, more ROUTE REQUESTS are sent to reconstruct
routes. This causes the Normalized Routing Load to increase
in DSR which is supported by our experimental results as
shown in Figure 4 The Normalized Routing Load is maximum
for DSR routing in Exponential and Pareto traffic. In case of
Constant Bit Rate(CBR) traffic, the packets are generated at
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Proceedings of 2011 International Conference on Signal Processing, Communication, Computing and Networking Technologies (ICSCCN 2011)
a constant rate. So, the Normalized Routing Load is very less
for both AODV and DSR routing.
C. Throughput of the network
Fig. 5. Throughput in AODV and DSR routing for different traffic models
in RPGM
Within the simulation time, many data packets are forwarded and received by the different nodes. The throughput
of the network denotes the average duration of packets per
seconds. i.e. the total number of packets flow in the network
per second.
� ℎ����ℎ��� =
����� ���� �������
����� ���������� ����
(4)
In Figure 5, we have shown that the throughput rate of
AODV routing is higher than the DSR in Constant bit rate
(CBR),Pareto and Exponential traffic model. The throughput
is very low and almost same in DSR for all types of traffic
models. This is because the routing overhead is high in
DSR than the AODV routing protocol. This has led to the
frequent route failures and the protocol needs to search for
next alternate route to the destination in DSR rather than in
AODV routing protocol. This results in low throughput.
VII. C ONCLUSION
In this article, we have tried to analyze the behavior of reactive routing protocols for different nodes following Reference
Point Group Mobility model. Along with popular Constant Bit
Rate traffic, we have also simulated the Exponential and Pareto
traffic sources. The exponential and Pareto traffic sources may
be congenial for multimedia applications. We found through
our simulations that the packet delivery fraction for reactive
routing remains same across all traffic patterns. The throughput
increases for exponential traffic in AODV routing. The normalized routing loads on nodes have increased with Exponential
and Pareto traffic patterns. The current study have considered
only the reactive routing protocol, the same study can be done
for proactive routing protocols like Destination Sequenced
Distance Vector (DSDV) routing algorithm also. The authors
are currently engaged in supplementing the current routing
protocols for multimedia application using Exponential and
Pareto traffic sources.
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