International Conference on Magnetics, Machines & Drives (AICERA-2014 iCMMD)

Mobility Based Comparison of Routing Protocols in Mobile Ad-hoc Networks

Arathy O PG Scholar, Communication Engineering

Amal Jyothi College of Engineering, Kanjirappally arathygpnth33@gmail.com

Binu Mathew Assistant Professor

Amal Jyothi College of Engineering, Kanjirappally binumathew@amaljyothi.ac.in

Abstract— Mobile wireless nodes without any controlling stations forms a Mobile Ad-hoc Network. Routing in MANET is an important issue to be considered. There are various routing protocols are developed for MANET. Selection of good protocol yield very good results. Another important consideration is the mobility models for the node movement. In this paper the routing protocols are compared based on various mobility models. As the mobility model changes the delay of the protocol also varies. End to end delay is taken as the performance measure.

Index Terms— Mobile Ad-hoc Network (MANET), Routing Protocols, Mobility Models, AODV, DSDV, DSR

I. INTRODUCTION The need for wireless communication increases day by

day. Wireless nodes are efficient because it does not require any wired connection for the setting of the network. The main wireless networks are usually used is ad-hoc networks, which can be setup easily without any difficulties. Mobile ad-hoc networks are being widely used in wireless networks. In Mobile ad-hoc network (MANET) the nodes can move freely without any controlling stations [1]. The nodes can act as network element as well as routers for forwarding data from one mobile node to another mobile node. The routing of data from one node to another requires a routing protocol. Since the MANETs are self-configuring the resources associated with it is very limited. So we have to select a routing protocol which is best and reduces the usage of network resources. A node is a network terminal which may be mobile having the capability to communicate with other nodes through wireless ports. Thus every node can send and receive data packets through the channel. This makes the MANET substantially different from other wireless networks. The sending of data in MANET depends upon the routing capability of intermediate nodes. So it requires a multi-hop transmission of data. The peculiarity of nodes is, they are small and battery powered making it mobile and portable. Resources are constrained and we have to make it more reliable. This can be done via the modification of protocol. The mobility model can play an important role.

The movement of nodes in MANET is taken by mobility models. Various type of mobility models are developed for wireless networks. For each and every application the selection of routing protocol and mobility model changes. The criteria for selecting these two are also varies according to our requirement. Various performance metrics can be included for judging the fairness of the results. In this paper the simulations are done using a discrete event simulator, known as NS2. Here also there are various possibilities for selecting the simulation tool. For which NS2 is widely used for the simulation of wireless scenarios. It can be used for the visualization of the simulation scenario, and it can also be used for various modifications according to our wish. There are two languages are used in NS2 [6]. The scripts of simulation are in the form of Tool Command Language (Tcl) and source codes are done in C/C++ [5].

Proactive, Reactive and Hybrid routing protocols are suggested for MANET. No protocol works well in all environments. The performance changes as the requirement changes. The proactive routing protocols are usually used for networks with small number of nodes. Reactive routing protocols fall into the category of on-demand routing protocols. It forms a route only there is a requirement for that. It is suggested that it can be used for large and high mobility scenarios. Hybrid routing is another type in which both proactive and reactive routings are mixed proportionally. The route packets based on zones in which they use proactive route discovery inside the zones and reactive route discovery outside the zones.

II. ROUTING IN MANET In order to route packets between nodes there is a

requirement of a routing protocol. Routing protocol simplifies the task of sending data in any network. Various routing protocol performs this task in different ways. The selection of a good routing protocol is important. The routing protocol must dynamically adjust the variations of the topology because of the rapid changing scenarios occurring in MANETs. Routing protocols developed for Internet is not suitable for MANET since it cause large amount of overheads. A brief idea of routing protocols used for MANET is presented below.

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International Conference on Magnetics, Machines & Drives (AICERA-2014 iCMMD)

A. Destination Sequenced Distance Vector (DSDV)

Distance vector protocol is based on destination sequence number is termed as DSDV routing protocol. The sequence numbers are used to verify the freshness of a route. Because of this loop formation can be prevented and make it as a better protocol. Every node has an associated routing table which contain the information regarding the routing in a wireless network. Once the network is formed and given the protocol as DSDV, at first each node forms a table. After starting routing using DSDV it continues until the topography remains same. The changes cause the updating of routing table. Otherwise the correct destination becomes unreachable from the source.

The routing table is broadcasted to each and every

neighbour node of the source. This is the mechanism adopted in this protocol for sending data about the topography of the network. The topography change mainly refers to the link breakage or failure of the route. The information about topology can be send using full or incremental units. Thus this protocol increases routing load.

B. Ad-hoc On-demand Distance Vector (AODV) and Ad-

hoc On-demand Multipath Distance Vector (AOMDV) AODV is an on-demand routing protocol in which the

route is built only when it is needed. There is no controlling stations because of that each node should carry out the routing decisions. If a node knows the route to destination there is no need AODV and the packets are send on the route. But there is no route to destination there should be a route discovery process. In AODV the routes are found out by disseminating route request packets to the neighbouring nodes. It is notifications to the destination that a node is want to send data. When a node receives RREQ, if it is the destination it send a reply back to the source. The reply packet is known as the RREP. If it is not the proper destination and it knows a route to the destination it also initiates broadcasting of RREQ [6]. When an RREP packet is unicasted to the source there is the setting up of a reverse path to the source. Usually the routes are found out by flooding of Hello packets. In AODV the hello packets are disabled. It is because the Hello packets induce increase in routing overhead. RREQ is forwarded by flooding the request as shown in Fig. 1.

Fig.1. Flooding of RREQ in AODV.

Fig.2. Reverse Propagation of RREP in AODV.

The RREQ packet contains the source and destination

address, sequence numbers, broadcasting ID and other information regarding the routing in Ad-hoc networks. If a link is failed and the routing process cannot be completed, a RERR packet is send to the source. When receiving the RERR packet a node can understand the failure of the route. So RERR packet can initiates another route discovery process for finding another route to the destination. When the RREP packet reach the source a reverse path is being built from destination to the source. The sending of data from source to destination is done through this path. The reverse path obtained via the propagation of RREP packet is as shown in Fig. 2.

Ad-hoc networks are highly dynamic and decentralised,

so the routes may change regularly. In order to achieve full connectivity another protocol which is a modification of AODV known as Ad-hoc on-demand multipath distance vector routing protocol (AOMDV) is proposed. Multiple paths are found out by this protocol if all the routes are failed in the case of AODV. The next hop in AODV is replaced by next hop and hop count pairs of all nodes are included in AOMDV.

C. Dynamic Source Routing (DSR) This protocol is especially designed for wireless mesh

networks [1]. As similar to AODV the routes are discovered only when it is required. So it is an on-demand routing protocol. But as different from AODV it uses source routing. There are two main process are used in DSR for routing. They are Route discovery and Route maintenance procedure. Since it use source routing each node must cache the address of the routes. Based on the cached data at each node the routing is carried out. For sending a reply back to the source the destination must know all the way to the source. The packet header will contain the entire route to the destination. It will increase the overhead associated with routing.

The route maintenance procedure is initiated when there

is a break in the route to the destination. At that time the route till the break is truncated and a new discovery of route is initiated. This all process can be done dynamically that is why it is known as dynamic source routing.

International Conference on Magnetics, Machines & Drives (AICERA-2014 iCMMD)

III. MOBILITY MODELS The mobility model defines the physical scenario of the

network of nodes, movements, direction and speed. Mobility models are also developed to increase the efficiency of the wireless networks. There are various types of mobility models and the functionality differs for each and every model. As the mobility model changes the basic behaviour of the network and applications are also change accordingly. Sometimes it becomes application dependent. With the mobility model we can find a user position in any mobile environment, which is a very relevant task. The mobility model developed for cellular networks are not suitable for Mobile ad-hoc applications. The following are the different mobility models used for ad-hoc networks.

A. Random Waypoint Model Random way point model is a type of random mobility

model. But it is more realistic than random model. In this epoch and pause concepts are introduced to modify it to be more realistic. A mobile node in the scenario has a number of epochs [3]. Each epoch consists of a motion section and a pause section. The nodes are uniformly distributed in the simulation area. At start each node selects a coordinate for the movement, and undergoes the motion interval section. After reaching the destination the next section begins, known as the pause section.

Fig.3. Movement of Nodes using Random Waypoint Model.

Uniformly distributed speed has two extremes,

minimum speed and maximum speed. This is used in the motion section. The pause time also has two extremes which are also uniformly distributed. The pause time is selected from [0, maxPauseTime]. If the pause time is zero, then it is a usual random mobility model. Fig. 3 shows the mobility pattern of the random waypoint model.

B. Manhattan Grid Model It is a type of grid model and is introduced for various

networking models. A node moves only in selected paths. The simulation area can be divided into blocks by two parameters. Here also pause time is introduced. The main peculiarity of this model is that a specific parameter known

as the minimum speed of the mobile node is also defined. By this parameter the node can take the speed arbitrarily as zero. Grid in Manhattan can have long paths with very slow speed of mobile node.

C. Gauss Markov Model Each mobile node in this model has to maintain two

separate values which are to be updated periodically. Speed and direction are taken as a vector in this model. This model is developed based on a tuning parameter. The starting positions of all mobile nodes are updated periodically. Normally the speed and direction is taken in to consideration and which is to be updated periodically. After the script is generated the field size is automatically updated as the movement starts.

D. Reference Point Group Mobility model This mobility model is a depiction of avalanche rescue

[3]. The mobile nodes are move with respect to a logical centre. The area under which the movement pattern can be found out based on the centre of movement of the nodes. Pattern of movement of nodes is shown in Fig. 4. In this the trajectory of 3 mobile nodes are shown. The position of nodes can be found out from the co-ordinate vectors.

Fig.4. Movement of Nodes using RPGM Model.

E. Static Scenario In this static scenario model by default nodes are

homogenously distributed over the simulation area. The parameters can be changed to obtain a non-homogenous scenario. For this an attraction point is defined and the area can be divided into several sections with varying density of nodes are also possible.

F. Probabilistic Random Walk Model The next position can be obtained by set of probabilities.

A probability matrix is defined which is the matrix which contain all the probabilities of the movement of the mobile node. Forward backward and still in both the x and y direction are also defined in this model. Node will travel with a fixed speed for a specific time once the direction of travel has been obtained. The model is as shown in Fig. 5. It shows the pattern obtained by only one node.

International Conference on Magnetics, Machines & Drives (AICERA-2014 iCMMD)

Fig.5. Movement of Nodes using Probabilistic Random Walk Model.

IV. SIMULATION ENVIROMENT In this section the details regarding the simulation of

routing protocols and mobility models are described. The simulations are done using a discrete event simulator known as Network Simulator version 2 (NS2.35). Table 1 shows the parameters of the network simulation.

TABLE 1. SIMULATION PARAMETERS

Simulation Parameters

Value

Simulator NS-2.35

Channel Type Channel/Wireless channel

Radio Propagation Model

Propagation/Two ray ground wave

Network Interface Type

Phy/WirelessPhy

MAC Type Mac/802.11

Interface Queue Type Queue/Drop Tail

Link Layer Type LL

Area(m*m) 500*500

Number of Nodes 25

The simulation scripts are written in Tcl code. Mobility

and a traffic files are loaded to the code for ease of comparison of various routing protocols and mobility models. The mobility file is the scenario generated for the mobility models described. These can be changed into corresponding NS file by giving proper commands. The number of nodes defining this simulation scenario is 25. Packet type selected for the simulation is constant bit rate traffic (CBR). The traffic file is generated using cbrgen.tcl NS2 file.

V. RESULTS AND ANALYSIS The performance of routing protocols when simulated

using various mobility models are as follows. The performance metric selected for the comparison is the end to end delay for transferring packets from one node to another. DSDV, AODV, AOMDV and DSR are taken for comparison. As protocol changes the end to end delay associated with the mobility model also changes. Table 2 shows the data obtained from the simulation, includes the delay associated with corresponding protocol.

From the comparison of mobility models for each of the protocol we can obtain the delay associated with mobility models. The mobility model with large delay is causing latency in sending packets. So in order to obtain a good mobility model we have to choose the model having low delay. Each of the mobility models having a certain type of movement pattern. A source node follow the movement pattern to the destination node then send the data packet.

TABLE 2. END TO END DELAY OF PROTOCOLS WITH MOBILITY MODELS

Mobility Models

End to End Delay

DSDV AODV AOMDV DSR

RWP 6.159 6.17 6.193 6.174

MG 6.163 6.234 6.181 6.173

GM 6.185 6.237 6.193 6.174

RPGM 6.164 6.177 6.161 6.172

STATIC 6.174 6.174 6.19 6.173

PRW 6.171 6.171 6.235 6.174

From the comparison of mobility models for DSDV routing protocol we can identify the model having low delay. DSDV which is a proactive routing protocol, each node in the network has a routing table for the transferring of data. In DSDV the model having low delay of 6.159 is the Random Waypoint model as shown in Fig. 6. By choosing this model for the movement of nodes can reduce the delay in sending the packets. For AODV also the RWP works with low delay of 6.17 as shown in Fig. 7. But AODV is an on-demand routing protocol. As seen from the figures Fig. 8 and Fig. 9, Reference Point Group Mobility (RPGM) model is having low end to end delay. For AOMDV about 6.16 and for DSR it is about 6.17. For these two protocols the model having capability of forming dynamic group will works with low delay

International Conference on Magnetics, Machines & Drives (AICERA-2014 iCMMD)

Fig.6. Mobility Model Comparison of DSDV Routing Protocol

Fig.7. Mobility Model Comparison of AODV Routing Protocol

Fig.8. Mobility Model Comparison of AOMDV Routing Protocol

Fig.9. Mobility Model Comparison of DSR Routing Protocol

VI. CONCLUSION In this paper mobility and routing in MANET is taken

into consideration. By analysing it using various mobility models and performing comparison between them obtain a result that helps us to select proper model for a routing protocol. The comparison is done using major routing protocols and important mobility models. A set of simulation scripts are generated and the mobility generation done using Bonn Motion, which is a scenario generation tool. We can select Random way point model for DSDV and AODV with low end to end delay. AOMDV and DSR, we can choose RPGM as the mobility model with smaller end to end delay. The comparison result shows that RWP works well for both Proactive and Reactive routing protocol. As a future work we can modify any of the protocol in NS2 for further improvement.

REFERENCES

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