Convergence Time Evaluation of AODV and AODV G in MANETs by ijcsis


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									                                                               (IJCSIS) International Journal of Computer Science and Information Security,
                                                                                                                 Vol. 8, No. 5, August 2010

        Convergence Time Evaluation of AODV and
                 AODV+G in MANETs
Annapurna P Patil                                                                                                  Harish.R
                                       Department of Computer Science and Engineering,
                                     M.S. Ramaiah Institute of Technology,Bangalore-54,India.                                                                               

Abstract     -Wireless mobile ad-hoc networks are characterized            WiFi-ready notebook PCs( MANET nodes) owned by rescue
as networks without any physical connections. In these networks            volunteers themselves to construct a MANET to support such
there is no fixed topology due to the mobility of nodes,                   a need.
interference, mulitpath propagation and path loss. Hence a                           MANET can be classified based on the
dynamic routing protocol is needed for these networks to
                                                                           communication pattern or the devices used, the variants of
function properly. Many routing protocols have been developed
for accomplishing this task. Selecting most appropriate routing            MANETs on the type of devices are sensor and ad hoc
protocol for a particular network scenario is the critical issue.          networks. Routing is one of the critical issue in MANET.
          Most attempts made at evaluating these algorithms so             Selecting the energy efficient routing protocols improves the
far have focused on parameters such as throughput, packet                  performance of the communication. The routing protocols are
delivery ratio, overhead etc. An analysis of the convergence               classified into three types. Proactive protocols maintain
times of these algorithms is still an open issue. The work carried         routing information for all the destinations, and keep updating
out fills this gap by evaluating the algorithms on the basis of            this information through periodic updates, an example for this
convergence time.                                                          protocol is DSDV[1],OLSR[3]. Reactive protocols don’t
           In this paper we present and examine the convergence
                                                                           maintain information for all the destination, rather they
time evaluation of routing protocols AODV and AODV+G . The
algorithm performances are compared by simulating them in                  discover the route to a destination on demand, an example for
ns2. Tcl is used to conduct the simulations, while perl is used to         this protocol is AODV[2]. Hybrid protocols attempt to
extract data from the simulation output and calculate                      combine the advantage of both proactive and reactive
convergence time. After extensive testing we observed that                 protocols, an example for this protocol is TORA[5], ZRP[4],
AODV+G converged well in all situations than AODV. The                     MPOLSR[6]. AODV+G[7] reduces unnecessary traffic will
paper also evaluates the algorithms using the rudimentary                  effectively improve the efficiency of those mobile nodes in
metrics-throughput and packet delivery ratio.                              network.
                                                                                     AODV and AODV+G protocols performs differently
Keywords- Routing Protocols, MANETS, Convergence Time.
                                                                           under different network scenarios. One protocol might
                                                                           perform better than others in specific situation. These
                     I. INTRODUCTION                                       protocols are compared in terms of convergence time to
                                                                           uncover in which situations these types of algorithms have
          A Mobile Ad-Hoc Network (MANET) is a self-                       their strengths and weaknesses.
configuring network of mobile nodes connected by wireless
links, to form an arbitrary topology. The nodes are free to                                    II. RELATED WORK
move randomly. Thus the network's wireless topology may be
unpredictable and may change rapidly. Minimal                                       There are many other works which are related to our
configuration, quick deployment and absence of a central                   work in evaluating routing algorithms. [7] AODV and
governing authority make ad hoc networks suitable for                      AODV+G has been compared in terms of Average delay,
emergency situations like natural disasters, military conflicts,           Packet delivery ratio, Normalized routing load and Routing
emergency medical situations etc .                                         load reduction, but not in terms of convergence time. [8]
          Every device in a MANET is also a router because it              AODV and DSDV has been compared in terms of
is required to forward traffic unrelated to its own use. Almost            convergence time. Many papers have compared AODV with
every year, the world is struck by numerous catastrophic                   other routing algorithms. In [9] AODV and DSDV have been
natural disasters, such as earthquake, hurricane, typhoon,                 compared with average throughput, packet loss ratio, and
tsunami, etc. In such a situation communication systems,                   routing overhead as the evaluation metrics, [10] has compared
fixed or mobile, were usually down due to various reasons.                 AODV and DSDV in terms of delay and drop rate, [11]
The loss of communication systems as well as information                   compares AODV and DSDV in terms of throughput, packets
networks made the rescue operation extremely difficult.                    received, delay and overload. Similarly, [12] compares

                                                                                                     ISSN 1947-5500
                                                            (IJCSIS) International Journal of Computer Science and Information Security,
                                                                                                              Vol. 8, No. 5, August 2010

AODV, DSDV and DSR in terms of throughput, delay, drop                  network, here GOSSIP3(.65,1,1) is used. The timeout period
rate.                                                                   of GOSSIP3 should be big enough to allow neighboring
                                                                        nodes to gossip. The NODE_TRAVERSAL_TIME parameter
             III. PROTOCOL SPECIFICATION                                of AODV is a conservative estimate of the average one hop
                                                                        traversal time for packets that includes queuing delays,
         This section gives the small presentation of two               interrupt processing times and transfer times. GOSSIP3 is not
protocols we evaluate in this paper.                                    used in the expanding-ring search with a smaller radius, since
                                                                        flooding is more efficient than gossiping for zone with small
A. AODV                                                                 radius because of the back-propagation effects[17]. The
         The Ad-hoc On-Demand Distance Vector (AODV)                    variant of AODV that uses GOSSIP3 is called AODV+G.
routing protocol is designed for use in ad-hoc mobile
networks. AODV is a reactive protocol: the routes are created
only when they are needed. It uses traditional routing tables,            IV SIMULATION AND PERFORMANCE ANALYSIS
one entry per destination, and sequence numbers to determine
whether routing information is up-to-date and to prevent                A. Environment and Assumption
routing loops.
         An important feature of AODV is the maintenance                Simulator chosen : The proposed algorithms are simulated on
of time-based states in each node: a routingentry not recently          NS2(version 2.33)[13]. NS2 is popularly used in the
used is expired. In case of a route is broken the neighbours            simulation of routing and multicast protocols, among others,
can be notified. Route discovery is based on query and reply            and is heavily used in ad-hoc networking research. ns
cycles, and route information is stored in all intermediate             supports an array of popular network protocols, offering
nodes along the route in the form of route table entries. The           simulation results for wired and wireless networks alike. It
following control packets are used: routing request message             can be also used as limited-functionality network emulator. It
(RREQ) is broadcasted by a node requiring a route to another            was necessary to use available implementations of algorithms
node, routing reply message (RREP) is unicasted back to the             rather than implement them freshly ourselves, as it is
source of RREQ, and route error message (RERR) is sent to               important for the acceptance of an evaluation that the
notify other nodes of the loss of the link. HELLO messages              implementation used for evaluation has been scrutinized and
are used for detecting and monitoring links to neighbours.              accepted as correct by the community. Else the evaluation
                                                                        results will not be accepted as doubt will exist about the
B. Gossiping & AODV+G                                                   correctness of the implementation of the algorithms

          The basic gossiping protocol is simple. A source              Algorithms chosen : Here in this paper we have selected to
sends the routing request with probability 1. When a node               simulate and evaluate the performance of AODV and
first receives a routing request, with probability p it                 AODV+G protocols. AODV is a reactive routing protocol and
broadcasts the request to its neighbors and with probability 1          AODV+G is variant of AODV routing protocol with
– p it discards the request; if the node receives the same rout         GOSSIP3. Further experiments can be built based on the
request again, it is discarded. Thus, a node broadcasts a given         results of this project, to compare convergence time
route request at most once. [7] proposes GOSSIP(p,k,m), an              performance of algorithms within the same category as well.
extension to the basic gossiping, and suggests that:
A node broadcasts with probability 1 for the first k hops               Mobility model : The Random Waypoint model is the most
before continuing to gossip with probability p.                         commonly used mobility model in research community. At
If a node with n neighbors receives a message and does not              every instant, a node randomly chooses a destination and
broadcast it, but then does not receive the message from at             moves towards it with a velocity chosen randomly from a
least m neighbors within a reasonable timeout period, it                uniform distribution [0,V_max], where V_max is the
broadcasts the message to all its neighbors [7].                        maximum allowable velocity for every mobile node. After
          Hass et al. implements GOSSIP(p,k,m) in Ad Hoc                reaching the destination, the node stops for a duration defined
On-Demand Distance Vector protocol (AODV) [18], a typical               by the 'pause time' parameter. After this duration, it again
and well-studied on-demond routing algorithm suited for                 chooses a random destination and repeats the whole process
mobile nodes routing in ad hoc network. We refer this gossip-           until the simulation ends.
based AODV as AODV+G. The experiments in [7] shows                                To create Mobile node Movement Scenario files, the
that gossiping can reduce control traffic up to 35% when                command line that needs to be run under directory : ns-
compared to flooding and the most significant performance of            allinone-2.33/ns-2.33/indep-utils/cmu-scen-gen/setdest :
GOSSIP is achieved by taking p=0.65, k=1 and m=1.                       ./setdest [-n num_of_nodes] [-p pausetime] [-s maxspeed] [-t
          In AODV+G, if the expanding-ring search with a                simtime] [-x maxx] [-y maxy] > [output-file][14].
smaller radius fails, rather than flooding to the whole

                                                                                                  ISSN 1947-5500
                                                              (IJCSIS) International Journal of Computer Science and Information Security,
                                                                                                                Vol. 8, No. 5, August 2010

Traffic pattern : Moreover, traffic sources may generate                  of detection of an interface being down. This failure event is
packets at constant bit rate (CBR), or at variable bit rate               said to end when the listener receives link state PDUs from
(VBR). The CBR class is commonly used for voice and data                  both ends of the link.
services. In this context, the data rate and the delay remain                       We arrive at the convergence time by measuring the
constant during the packet transmission. More particularly,               interval between the detection of route failure and successful
CBR traffic sources provide a constant flow of data packets of            arrival of a packet at the destination over the newly computed
512 bytes with a transmission rate of 4 packets per second.               route. This includes not only the routing convergence time,
All CBR traffic scenarios are generated using cbrgen.tcl in               but also the time taken for the packet to traverse the network
NS-2                                                                      from the source to the destination over the newly discovered
          To create CBR traffic scenario files, under directory           path. Since this is a comparative analysis, and both the
:ns-allinone-2.33/ns-2.33/indep-utils/cmu-scen-gen/cbrgen.tcl             routing protocols use shortest distance with number of hops as
./ns cbrgen.tcl [-type cbr|tcp] [-nn nodes] [-seed seed] [-mc             the metric for distance calculation, both protocols will arrive
connections] [-rate packet/second for one connection] >                   at the same new route, and the time taken to reach the
[output-file][14].                                                        destination over this new route will be the same (since all
                                                                          physical characteristics are the same). Hence this extra time
Network scenario : The simulations are conducted using the                measured does not affect the comparative analysis.
network simulator ns2 [14]. Random Waypoint mobility                                In any case, the time taken for a packet to travel from
model is used. The physical layer simulates the behavior of               the source to the destination is negligible when compared to
IEEE 802.11 (as included with ns2). Each node has a radio                 the time taken for the algorithm to discover the new route,
range of 250 meter, and uses TwoRayGround as the radio                    either through route request – route reply sequences as in
propagation model.                                                        reactive protocols, or by waiting for an update that contains
All the scenarios are based on the following basic parameters:            new route information as in proactive protocols. Also, this
cbr (constant bit rate) traffic                                           automatically verifies that the new path calculated is correct.
topology of size 500 m x 500 m                                                      The cycle of invalidation of old path and discovery
maximum speed of each node 20 m/s                                         of a new path might occur many times, and for many source-
simulation time 180s                                                      destination pairs over the course of the simulation. Hence the
transmission rate (packet rate) 10 m/s                                    average value of these times is taken as the convergence time
The number of nodes is varied in the range [10,100] in steps              of that algorithm for that scenario.
of 10 (to represent 10 node densities). Pause time is varied in           This procedure has been carried out in perl.
the range [0,180] in steps of 20 (to represent 10 pause times).
                                                                          Throughput : If y number of packets delivered within t time
B. Performance Metric                                                     at a node then the throughput at the node could be defined as
                                                                          y/t. By definition, the throughput needs to be calculated at the
    A trace file contains a lot of information which may not be           bottleneck node, not sender. For the throughput calculation, in
required to analyze the performance of the protocol. We are               general divide the successfully received packets by the
always interested in some amount of information that is                   simulation time will give the answer. In the trace file there are
sufficient to predict the efficiency of the protocol. The                 different levels of received packets such as the RTR or AGT
following performance metric is needed to be taken into                   level. The packets received by the node in its AGT level will
consideration in order to analyze and compare the                         be the real received packets. Here these packets are filtered
performance of AODV and AODV+G                                            from the trace file using perl script.

Convergence Time : In [15], convergence time has been                     Packet Delivery Ratio : The ratio between the number of
defined as the time between detection of an interface being               packets successfully received by the application layer of a
down, and the time when the new routing information is                    destination node and the number of packets originated at the
available. [16] defines a route convergence period as the                 application layer of each node for that destination.
period that starts when a previously stable route to some
destination becomes invalid and ends when the network has
obtained a new stable route for. Similarly, we define                                   V. EXPERIMENTAL RESULTS
convergence time as the time between a fault detection, and
restoration of new, valid, path information.                                       Graphs are one of the ways to analyze and compare
          [15] calculates convergence time in the IP backbone.            the results of the trace file. Other methods can also be used
The authors arrive at the value of convergence time by                    for comparison like tabular form showing required output
deploying entities called ‘listeners’, which listen to every link         data of the trace file. Simple MS Excel or MATLAB also
state PDU being sent by the is-is protocol. The time when the             work for plotting graphs. In this paper the graphs are plotted
first ‘adjacency down’ packet is observed is taken as the time            using xgraph in NS2.

                                                                                                     ISSN 1947-5500
                                                            (IJCSIS) International Journal of Computer Science and Information Security,
                                                                                                              Vol. 8, No. 5, August 2010

         In order to be able to cover most if not all the types
of scenarios the algorithms might face, we varied both the
node density (number of nodes) and the node mobility (pause
time). The node density (number of nodes) was varied in the
range [10,100] in steps of 10 (10 different node densities).
    The upper limit of this range was chosen to be 180
because the simulation time is 180s in all the cases. Thus a
pause time of 180 implies that the nodes pause in their initial
positions for 180 seconds – the entire duration of the
simulation. Hence this represents the case where nodes are
completely static. Similarly, pause time 0 represents very high
mobility where the nodes are in constant motion. Thus we
tested each algorithm over 10 node densities x 10 pause times
= 100 scenarios.

A. Convergence Time                                                              Figure 3: 30 nodes, varying pause time

    Convergence time of AODV and AODV+G is calculated
using perl script. This script parses trace file created by
simulating AODV and AODV+G algorithms to calculate
convergence time. In each graph, the node density is fixed
and the pause time is varied.

                                                                                 Figure 4: 40 nodes, varying pause time

           Figure 1: 10 nodes, varying paused time

           Figure 2: 20 nodes, varying pause time                               Figure 5: 50 nodes, varying paused time

                                                                                                 ISSN 1947-5500
                                               (IJCSIS) International Journal of Computer Science and Information Security,
                                                                                                 Vol. 8, No. 5, August 2010

     Figure 6: 60 nodes, varying paused time
                                                                    Figure 9: 90 nodes, varying paused time

     Figure 7: 70 nodes, varying paused time

                                                              Figure 10: 100 nodes, varying paused time

                                                                  Based on the above figures it is found AODV+G
                                                         convergence time is less than AODV in all assumed network
                                                         scenarios. It is also found that as the pause time increases the
                                                         convergence time of AODV+G decreases. Convergence time
                                                         of both AODV and AODV+G increases as the node density

                                                         B.. Throughput

                                                                  Here node density is varied from 10 to 100 in steps
                                                         of 10 nodes. For each node density both the algorithms are
                                                         simulated with varied paused time from 0s ts 180s in steps of
Figure 8: 80 nodes, varying paused time                  20s. Average throughput in each node density is taken and the
                                                         graph is plotted as show in figure 12.

                                                                                    ISSN 1947-5500
                                                          (IJCSIS) International Journal of Computer Science and Information Security,
                                                                                                            Vol. 8, No. 5, August 2010

                                                                                                VI. CONCLUSION

                                                                               AODV and AODV+G mobile Ad-hoc routing
                                                                      protocols have been presented and evaluated using well know
                                                                      network simulator NS2( version 2.33 ). AODV+G is gossip
                                                                      based AODV, here GOSSIP3(.65,1,1) is used. These two
                                                                      protocols are evaluated using the network performance metric
                                                                      convergence time. Here we observed that AODV+G
                                                                      converged well than compared to AODV in all assumed
                                                                      network scenarios. We also noticed that with the very low
                                                                      node density throughput and packet delivery ratio of AODV
                                                                      is more than AODV+G. With node density more than 30
                                                                      nodes AODV+G performs better than AODV. We can extend
                                                                      our work to compare the performance of Adaptive Gossip-
    Figure 12: Throughput AODV Vs AODV+G
                                                                      based Ad Hoc Routing (AGAR) with Gossip-based Ad Hoc
                                                                      Routing (AODV+G) using convergence time, throughput and
        From the above figure we observed that AODV with              packet delivery ratio.
the low density performance well than AODV+G. As the
node density increases AODV+G throughput increases. With                                        ACKNOWLEDGMENT
the node density more than 30 nodes the throughput of
AODV+G is almost double than AODV.                                       We wish to acknowledge our Principal Dr K Rajanikanth,
                                                                      M. S .Ramaiah Institute of Technology,Bangalore-54 and
C. Packet Delivery Ratio                                              Professor and Head of the Department at CSE Prof .V.
                                                                      Muralidharan for their encouragement which helped us
         Here node density is varied from 10 to 100 in steps          produce this work..
of 10 nodes. For each node density both the algorithms are
simulated with varied paused time from 0s ts 180s in steps of                                   VII. REFERENCES
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                                                                                                       ISSN 1947-5500
                                                                          (IJCSIS) International Journal of Computer Science and Information Security,
                                                                                                                            Vol. 8, No. 5, August 2010

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                           AUTHORS PROFILE

The authors are Faculty and Post graduate Student at M S
Ramaiah Institute of Technology, Bangalore working in the
area of performance evaluation of routing algorithms at the
R&D labs, Department of Computer Science and

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