2010 2nd International Conforence on Education Technology and Computer (ICETC)

Implementation and Performance Evaluation of

AODV in Wireless Mesh Networks using NS-3

Arnrita Bose Paul, Shantanu Konwar,Upola Gogoi, Angshuman Chakraborty, Nilufar Yeshrnin.

Department of Computer Applications, Assam Engineering College,

Guwahati, Assam, India. E-mail: {amritabosepaul, shantanu.220984, upola.aec,

angshuchakra, nilu.yesh}@gmail.com.

Abstract- Wireless Mesh Networks (WMNs) are a radio-based network technology that has gained considerable importance in network research community. It is a multi-hop wireless access network where nodes can act both as a host as well as a router. One of the factors that influence the performance of

WMNs is the underlying routing protocol used. Since implementation of wireless routing protocols in a real test bed is difficult, hence, simulation environment is being considered for performance evaluation of a routing protocol in a wireless

scenario. Recently, a new network simulator called NS-3, which is in its developing stage, demands a great potential (as claimed by the developers group) for performance analysis of different routing protocols. In this paper, we aim to implement

and analyze the performance of Ad hoc On-Demand Distance Vector (AODV) routing protocol in NS-3, which is one of the candidate routing protocol proposed by IETF group for WMNs. For this, we have implemented AODV in NS-3.6 and

extensive simulations have been carried out for calculation of Throughput, Packet Delivery Ratio (PDR), and Normalized Routing Overhead (NRO).

Keywords- WMNs, AODV, WLANs, NS-3, NRO, PDR, IETF.

I. INTRODUCTION Wireless Mesh Networks (WMNs) have emerged as one

of the most promising technology [1] [8] [9] for providing robust and reliable broadband Internet applications. This type of network is characterized by self organizing, self configuring, and require minimal upfront investment in deployment. One of the important factors influencing network performance is the underlying routing protocol used for forwarding data packets within the network. Routing in WMNs is a challenging job due to its dynamically changing topology of client nodes. There is as such no dedicated routing protocol developed for WMNs, so it has become important to cite out a routing protocol which suits best in the WMNs scenario.

Considering the dynamically changing nature of client nodes, it has been felt that a reactive routing protocol would have better adaptability for client WMNs [1]. In this paper, we aim to implement and analyze the performance of Ad hoc On-Demand Distance Vector (AODV) routing protocol, which is one of the candidate routing protocol proposed by IETF group for WMNs [6]. Moreover, AODV has been

Sukurnar Nandi

Department of Computer Science & Engineering, Indian Institute of Technology Guwahati,

Guwahati, Assam, India. E-mail: sukumar.nandi@gmail.com.

found to outperform DSR [3] in heavy traffic load and high mobility scenarios [3] [4] [10].

Simulation is one of the important tool for assessing the performance of routing protocols in a Wireless scenario. Till date, the performance evaluation of most ad hoc routing protocols has been carried out in a simulation test bed using NS-2 [12]. Recently, a new network simulator called NS-3 [5], which is in its developing stage, demands a great potential (as claimed by the developers group) for performance analysis of different routing protocols. Available release of NS-3.6 is lacking AODV routing protocol in it. NS-3 developers group is designing the code for AODV but not ported in NS-3.6 release as the code is in its testing stage. We have implemented AODV code in NS-3.6 and extensive simulations have been carried out for its performance evaluation in terms of throughput, Packet Delivery Ratio (PDR), and Normalized Routing Overhead (NRO).

The rest of the paper is organized as follows: Section II and section III deals with the comprehensive analysis of WMNs and AODV protocol for client WMNs respectively. A brief summary of Network Simulator called ns-3 has been discussed in section IV. Performance analysis of the protocol is presented in section V. Finally, section VI concludes the paper.

II. WIRELESS MESH NETWORKS By defmition, Wireless Mesh Network (WMN) is a set of

wireless nodes that can communicate with each other, forwarding each other's packets. Each node operates both as a host and as a wireless router [2]. Clients can connect to WMNs routers using common networking interfaces (e.g., Ethernet, 802.11, Bluetooth). Nodes exchange information only with its neighbors, thus coverage of the network depends on the underlying radio technology, number of nodes and their location in relation to one another. There is no infrastructure required to roll-out such a network, therefore the deployment cost is low as compared to other WLANs. WMNs have the potential to deliver Internet broadband access, wireless local area network coverage and network connectivity for stationary or mobile hosts at low costs both for network operators and customers. They promise greater flexibility, increased reliability, and improve

978-1-4244-6370-11$26.00 © 2010 IEEE V5-298

20i 0 2nd international Conforence on Education Technology and Computer (ICETC)

perfonnance over conventional WLANs. WMNs have potential for reliability because they follow a completely decentralized approach. When a single node goes down its neighbors simply fOld another route around it. The main characteristic of WMNs is communication between nodes over multiple wireless hops on a meshed network graph. Efficient routing protocol provides paths through the wireless mesh and react to dynamic changes in the topology, so that mesh nodes can communicate with each other even if they are not in direct transmission range. Intennediate nodes along this path forward packets to the destination.

The architecture of WMNs can be classified into three main groups based on the functionalities of nodes [1]:

• Infrastructurelbackbone WMNs: This type of WMNs includes mesh routers fonning an infrastructure backbone for clients that connect to them. Widely used radio technology in WMNs is IEEE 802.11. Mesh routers fonn a mesh of self­configuring, self-healing links among themselves. Some mesh routers are mounted with gateway functionality for connecting the backbone to the Internet.

• Client WMNs:

•

A mesh router is not required for these types of architecture. Here client nodes constitute the actual network to perfonn routing and configuration functionalities as well as providing end-user applications to customers. It is basically a peer-to­peer network among client devices. In client WMNs, nodes consists of one type of radio only, so requirements on end-user devices are increased as compared to infrastructure meshing since they have to perfonn additional functions such as routing and self-configuration.

Hybrid WMNs: Hybrid architecture is the combination of infrastructurelbackbone and client meshing. Mesh clients can access the network through mesh routers as well as direct meshing with other mesh clients is also pennissible in this architecture.

""'--.. I\d"" ... .....

t!tAou..:<>u._ .... ,lt.

Figure I. Hybrid WMNs Architecture

III. AODV FOR CLIENT WMNs AODV routing protocol is reactive in nature [11]. Nodes

in AODV request a route only when it needs one. It allows multi-hopping among the actively involved nodes that wants to establish and maintain an ad-hoc network. AODV is based upon Distance Vector Algorithm. Thus, nodes that are not active members of the communication process need not keep a route to the destination. AODV uses three types of messages to discover and maintain links.

• Route Request (RREQ) • Route Reply(RREP) • Route Error(RERR)

Any node that wants to fOld a route to another node, broadcasts a Route Request (RREQ) to all its neighbor nodes. The RREQ traverses through the network until it reaches the destination node or to a node that has a valid route to the destination. Then, a route is made available back to the source by unicasting a Route Reply (RREP) message [7].

AODV keeps track of the following infonnation for each routing table entry.

• Destination IP Address - IP address for the destination node.

• Destination Sequence Number - Sequence Number for this destination.

• Hop Count - Number of hops required for reaching the destination.

• Next Hop - Neighbor node that has been selected to forward packets to the destination.

• Lifetime - Time period during which a route is assumed to exist.

• Active Neighbors List - Neighbor nodes actively using the route table entry.

• Request Buffer - Used for ensuring that a particular request is processed only once.

Route Establishment: Whenever a node wants to send packets to a destination

node whose route is unknown, or the previously existing route has become invalid, the source node has to broadcast a RREQ to all its neighboring nodes. The requesting node will wait for a RREP. Within a specified time interval, if the source node does not receive the RREP, it will rebroadcast the RREQ or will assume that no route exists to the destination. When a neighboring node receives the RREQ but does not have a valid route to the destination, it will rebroadcast the RREQ to its neighboring nodes. This is called forwarding of RREQs. The forwarding node also keeps a temporary reverse route to the Source IP Address in its routing table entry. This is essential to forward the RREP back to the requesting source node. When the RREQ reaches the destination or any intennediary node that has a valid route to the destination, a RREP is unicasted back to the source node. When the RREP reaches the source node a valid route exists between the source and the destination [7].

V5-299

20i 0 2nd international Conference on Education Technology and Computer (ICETC)

Route Maintenance: AODV uses special HELLO messages [11] to keep track

of the neighbor nodes, which is broadcasted by each active node taking part in the communication process to indicate its presence in the network. When any node stops sending HELLO messages to its neighbors, the neighbor nodes assumes a link breakage with that particular node, and sends a RERR message to all other active nodes using that route [7]. The nodes which receive this message can then either stop sending data to that particular node or request for a new route by sending a new RREQ.

IV. ABOUT NS-3 NS-3 is a discrete event-driven network simulator for

Internet systems, targeted primarily for research and educational community. It helps researchers to study Internet protocols and large-scale network systems in a controlled environment. NS-3 has the following features for performing simulations [5].

• It is written in C++ with optional Python interface. Project focus to date has been on setting the long-term architecture rather than developing new models.

• Research generally involves both simulations as well as test bed implementation. If the simulator is not able to closely relate a model to a real system it would be hard to compare results or validate the model. NS-3 provides solution to this problem by modeling nodes like a real computer and supporting key interfaces such as sockets API and IP/device driver interface (in Linux). It also allows reuse of kernel and application code.

• It allows software integration that conforms to standard input/output formats enabling other tools to be reused such as pcap trace output, ns-2 mobility script and has also added support for running implementation code. With Wireshark, NS-3 trace can be viewed.

• NS-3 provides integration with real systems that provide better support for the researcher moving between simulation and test beds or live experiments.

• It has a new tracing model that decouples trace sources from trace sink. Various trace sources for packet receptions, state machine transitions are implemented in the system.

• NS-3 includes a well documented attribute system in which object attributes are organized and documented in the Doxygen.

V. PERFORMANCE EVALUATION

A. Assumptions:

Our simulation model is based on the following assumptions:

• Client Mesh Architecture as depicted in Fig. 2.

Figure 2. Client Mesh Architecture

• All Nodes are mobile. • Each node can behave both as a client and a

router. • Since it is a Client WMN scenario all nodes are

wireless and in Adhoc mode. • All nodes are having a single interface and

running AODV protocol in that interface. • All nodes have same capabilities (i.e., same

coverage area, same antenna) but their functionalities are independent of one another.

• All nodes are randomly placed and follow a 2d­walk-mobility pattern.

• Traffic flows between participant nodes either directly or via any intermediary neighboring node.

• Nodes can either receive or transmit at a time. • There is no turnaround time between

transmitting and receiving; nodes can switch between transmit and receive instantly.

• Mobility is uncorrelated among the nodes and links fail independently.

B. Simulation Environment:

Simulation Model:

Our AODV routing model is built on top of the IEEE 802.11 MAC model of NS-3 and random 2d-walk model is adopted for driving mobile clients. Random 2d-walk mobility model as described in [5] states that each instance moves with a speed and direction chosen at random with the user-provided random variables until either a fixed distance has been walked or until a fixed amount of time. If a node hits one of the boundary (specified by a rectangle) of the model, it rebounds on the boundary with a reflexive angle and speed. This model is often identified as a Brownian motion model.

In our simulation study, the speed is varied from 1 rnlsec to 2rn1sec. Each node maintains a routing table which is updated during the route discovery process of the protocol. Thus a dynamic on-demand route is calculated and selected for delivery of data packets. Table-l depicts the parameters set for the simulation model that is common for all our simulations. The other attributes of our simulation viz., number of nodes, mobility and traffic load are changed from scenario to scenario.

V5-300

20i 0 2nd international Conference on Education Technology and Computer (ICETC)

TABLE!. PARAMETERS FOR SIMULATION MODEL

Simulation Parameters Value

Simulator NS-3 (VERSION 3.6)

Operating System Linux (Fedora core II (64 bit»

Simulation Time 50 sec

Simulation Area IOOm x 100m

Number of Nodes 20 for sparse & 40 for dense

Transmission Range 50 meters

Movement Mode Random 2d-walk

Speed of Mobile Nodes I mlsec and 2 mlsec

Traffic Type CBR

Data Payload 512 bytes

Packet Rate 20 p/sec- 80 p/sec

Mac Layer 802.11 DCF with RTS/CTS

Radio Frequency 2.40Hz

Radio Channel Rate 2Mbps

Propagation Loss Model Friis Propagation Loss Model

Propagation Delay Constant Speed Propagation Delay Model Model

C. Performance Metrics We use the following perfonnance metrics to analyze the

AODV protocol in the Client WMNs scenario. • Throughput • Packet Delivery Ratio (PDR) • Nonnalized Routing Overhead (NRO)

D. Results and Analysis We have simulated AODV in different networking

scenarios using NS-3 simulator. The scenarios and results along with detailed analysis are presented below.

Scenario!: To analyze the perfonnance of AODV in tenns of

throughput, PDR and NRO in a sparse network comprising of 20 nodes, we perfonned simulation by varying number of data packets sent per second while keeping number of flows constant. Number of packets varied per flow ranges from 20 packets/sec to 80 packets/sec. Other parameters considered for simulations are same as referred in the Table-I.

Fig.3 depicts aggregate network throughput against increasing traffic load. It is observed that in case of sparse network, throughput decreases with increasing mobility of nodes. It can be explained by the fact that, due to increased mobility of nodes the packets intended for a destination are lost on the way because of displacement of intennediary nodes or the destination node itself.

0.4

0.35

------==== : • .....

;; "- 0.3

.s= ... " 0.25 0

� 0.2 .. __ 1m/sec .. 0.15 :."

:.. 0.1 __ 2m/sec ... ..

0.05

0

20 30 40 50 60 70 80

Packets/sec

Figure 3. Throughput (in sparse nlw)

It has been observed that as traffic load varies, network throughput for both mobility patterns increases to a certain point and then reaches a saturated point according to the network conditions, e.g. 50 packets/sec in the sparse network and thereafter maintains a steady state irrespective of increased traffic load.

� 0.9 e. 0.8 .g 0.7 : 0.6 � O.S

� 0.4

� 0.3 � 0.2 :. 0.1 o 20 30 40 50 60 70

Packets/sec

Figure 4. Packet Delivery Ratio (in sparse nlw)

FigA shows that PDR in a sparse scenario decreases gradually when the packet sending rate is increased. This trend in PDR of AODV is due to the buffering capacity of each node in the simulator. And as the mobility is doubled the PDR degrades gradually.

0.25,----------------

�

j 0.2 +------/-�---------� � � 0.15 +------,f---�-_r_-_"<_--..... -� � � 0.1 t----------------�

z

Packet.s I Second

Figure 5. Normalized Routing Overhead (in sparse n/w)

-+--1 mlsec

___ 2m/sec

Fig.5 shows the NRO for Sparse Networks in WMN scenario. Initially, NRO increases with increasing packet

V5-301

20i 0 2nd international Conforence on Education Technology and Computer (ICETC)

sending rate and at certain point it starts decreasing. In case of high mobility, higher NRO is observed. This behavior of NRO is due to the fact that AODV [2] creates routes on demand and control packet sending rate is high in a reactive protocol.

Scenario II: To analyze performance of AODV in a dense network

comprising of 40 nodes, we measure throughput, PDR and NRO. Simulation is carried out by varying number of data packets sent per seconds while keeping the number of flows constant. Numbers of packets varied per flow ranges from 20 packets/sec to SO packets/sec. Other parameters considered for simulations remain same as referred in Table-1.

0.7

.. 0.6 " � O.S

� 0.4

l 0.3

� 0.2

� 0.1

o

20 30 40 SO 60 70 80

Packets'sec

Figure 6. Throughput (in dense nlw)

�lm/sec ___ 2m/sec

Fig.6 depicts aggregate network throughput against increasing traffic load. Like sparse network, similar behavior is observed in dense network. But comparatively, throughput in case of dense network is found to be better than sparse network due to better availability of routes.

12

.. � 02

o

20 30 40 50 60 70

Packet/",c

Figure 7. Packet Delivery Ratio (in dense nlw)

Fig.7 shows the decrement of PDR with increasing packet sending rate. But as compared to sparse network, PDR is better in dense network and with high mobility PDR decreases gracefully. Fig.S shows NRO for a dense network. Initially, NRO decreases as the packet sending rate increases. It decreases to a certain point, and then it starts increasing and maintains a

0.2S

1 0,20

� � 0. 15

.� "'

... 0.10 -+-lm/sec

. � -+-2m/sec

1 O.os

z

0.00 '0 30 40 50 60 70

Packets I Second

Figure 8. Normalized Routing Overhead (in dense n/w)

nearly constant increase rate. In case of nodes having a speed of 2 mlsec, NRO is much higher than low mobility scenario. This behavior of NRO is due to the fact that AODV creates routes on demand and the control packet sending rate is high .

VI. CONCLUSION AND FUTURE WORK

Routing creates a communication path between source and destination nodes, and forward packets on that route. A protocol which ensures high throughput, high packet delivery ratio, and low overhead, in presence of changing networking conditions, is considered to be a good one for any networking scenario. In our work we have implemented AODV protocol in NS-3 for client WMNs and its performance has been evaluated through extensive simulations. From the obtained results, we conclude that AODV performs better in dense network than in sparse network for client WMNs. Random 2d-walk model is used in our simulation which can be termed as worst case behavior for random movement of nodes and conclude that performance of AODV cannot degrade beyond the simulated results we obtained via simulation.

We have used throughput, PDR and NRO as performance metrics to compare and analyze performance of AODV routing protocol. The other performance metric viz., End to End delay shall also be taken into consideration. We shall explore the effects of Random Way-Point model for node mobility in our future work.

ACKNOWLEDGEMENTS

The work has been carried out as a part of the Research and Development Project titled "Investigation of Security Issues in Wireless Mesh Networks and development of a Secure Routing and Authentication Protocol", funded by Department of Information Technology (DIT), Govt. of India.

REFERENCES

[I) I. F. Akyildiz, X. Wang and W. Wang, "Wireless mesh networks: a survey" Computer Networks, 47(4): 445-487, 2005.

[2) Tony Larsson and Nicklas Hedman, Master Thesis: Routing Protocols in Wireless Ad-hoc Networks - A Simulation Study, 1998.

V5-302

2010 2nd International Conference on Education Technology and Computer (ICETC)

[3] Samir R. Das, Charles E. Perkins, Elizabeth M. Royer and Mahesh K. Marina. "Performance Comparison of Two On-demand Routing Protocols for Ad hoc Networks." IEEE Personal Communications Magazine special issue on Ad hoc Networking, February 2001, p. 16-28.

[4] Mehran Abolhasan, Tadeusz Wysocki and Eryk Dutkiewicz, A review of routing protocol for mobile ad hoc networks, June 2003, doi: 10.10 16/S 1570-8705(03)00043-X.

[5] NS-3. http://www.nsnam.orgl.

[6] Ian D. Chakeres and Elizabeth M. Belding-Royer, AODV Routing Protocol Implementation Design, Proc. Of the 4th ACM international symposium on Mobile Ad hoc Networking and Computing, 2003.

[7] C. Perkins, E Belding-Royer and S. Das, Ad hoc on-demand distance vector (AODV) routing, RFC 3561, July 2003.

[8] M. L. Sichitiu, "Wireless Mesh Networks: Oppurtunities and challenges," in Proc. Of the Wireless World Congress, (Palo Alto,Ca),May2005.

[9] R. Bruno, M Conti, and W. Wang, "Mesh Networks: Commodity multihop ad hoc networks," IEEE communications Magazine, vol. 43, pp.l23-131,Mar2005.

[10] Saad Khan, Azad Amir Pirzada, and Marius Portmann, "Performance Comparison of Reactive Routing Protocols for Hybrid Wireless Mesh Networks", in The 2nd International Conference on Wireless Broadband and Ultra Wideband Communications (AusWireless 2007)

[II] C.Perkins, E. Belding Royer, and S. Das Ad-hoc On demand Distance Vector (AODV) routing, RFC 3561 IEEE communication Magazine, Vol. 43,pp. 123-131, July 2005.

[12] http://www.nsnam.orgldocs/ns-3-overview.pdf

V5-303