Performance Analysis of Routing Protocols in Mobile Ad Hoc Networks

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International Journal of Emerging Technology and Advanced Engineering

Website: www.ijetae.com (ISSN 2250-2459, ISO 9001:2008 Certified Journal, Volume 8, Issue 1, January 2018)

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Performance Analysis of Routing Protocols in Mobile Ad Hoc

Networks

Mona Sayed Mohmmed

1

, Ghassan M T Abdalla

2

1

Department of Electrical and Electronic Engineering, University of Khartoum, Sudan

2_{Department of Electrical and Electronic Engineering, University of Khartoum, Sudan, Tabuk University, KSA}

Abstract— A mobile Ad-Hoc network is a collection of autonomous wireless nodes without any fixed infrastructure and centralized administration. This paper evaluates the performance of Mobile Ad-Hoc Network Routing Protocols Dynamic Source Routing (DSR), Ad-Hoc On Demand Distance Vector (AODV) and Destination-Sequenced Distance Vector (DSDV) under different performance metrics like throughput, packets dropped, normalized routing overhead, end-to-end delay and optimal path length. The performance evaluation is done in different mobility scenarios and different traffic load using network simulator (NS-2). Protocol evaluations are based on the simulation of 50 wireless nodes forming an ad hoc network, moving over 1000m × 1000m flat space for 300 seconds of simulated time. From the results we note that DSR achieves performance better at low speed (v=1) and low traffic load (maximum number of connections =10) whereas DSDV has better performance when number of connections =20 and v=1 m/s. AODV gives better performance at high traffic (maximum number of connections =20) and high speed (v=20 m/s).

Keywords— Ad-Hoc network, AODV, DSDV, DSR, NS-2.

I. INTRODUCTION

An ad hoc network is a collection of wireless mobile nodes dynamically forming a temporary network without the use of any existing network infrastructure or centralized administration. In areas in which there is little or no communication infrastructure or the existing infrastructure is expensive or inconvenient to use, wireless mobile users may still be able to communicate through the formation of an ad hoc network. In such a network, each mobile node operates not only as a host but also as a router, forwarding packets for other mobile nodes in the network that may not be within direct wireless transmission range of each other. Each node participates in an ad hoc routing protocol that allows it to discover ―multi-hop‖ paths through the network to any other node [1, 2]. Such networks find applicability in disaster management environment, crowd control, military applications and conferences [3]. Routing is one of the major concerns in these networks due to its frequent changing topology and the absence of centralized administrator.

There are many ways to classify the mobile ad hoc network (MANET) routing protocols, depending on how the protocols handle the packet to deliver from source to destination. Routing protocols in MANETs are broadly classified into two types: proactive and reactive protocols. Table driven or proactive protocols maintain consistent, up to-date routing information from each node to every other node in the network. These protocols require each node to maintain one or more tables to store routing information. On demand or reactive protocols, the routes are created as and when required. When a source wants to send to a destination, it invokes the route discovery mechanisms to find the path to the destination. In addition they can be categorized by the number of paths they retain to each destination: single path or multipath. The single path category includes protocols such as Ad-Hoc On Demand Distance Vector (AODV), Temporally-Ordered Routing Algorithm (TORA), Destination-Sequenced Distance Vector (DSDV), where each node has just one path for each destination [4]. The rest of the paper is organized as follows, in the next section available routing protocols are reviewed; section 3 includes a description of the simulation model used. Section 4 introduces and discusses the performance evaluation metrics and simulation results. The paper is concluded in section 5.

II. ADHOCNETWORK ROUTING PROTOCOLS

In this section, the key features of the simulated protocols DSDV, DSR, and AODV protocols are introduced.

A. Destination-Sequenced Distance Vector (DSDV)

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Routing table updates are periodically transmitted throughout the network in order to maintain table consistency. The node also transmits its routing table if a significant change has occurred in its table from the last update sent. So, the update is both time-driven and event-driven. The routing table updates can be sent in two ways: - a "full dump" or an incremental update [5, 7]. A full dump sends the full routing table to the neighbors and could span many packets whereas in an incremental update only those entries from the routing table that have changed since the last update are sent. If there is space in the incremental update packet then those entries whose sequence number has changed may be included [7]. When the network is relatively stable, incremental updates are sent to avoid extra traffic and full dump updates are relatively infrequent. In a fast-changing network, incremental packets can grow big so full dumps will be more frequent [1]. Each route update packet, in addition to the routing table information, also contains a unique sequence number assigned by the transmitter. The route labeled with the highest (i.e. most recent) sequence number is used. If two routes have the same sequence number then the route with the best metric (i.e. shortest route) is used [6]. Nodes also keep track of the settling time of routes, or the weighted average time that routes to a destination will fluctuate before the route with the best metric is received. By delaying the broadcast of a routing update by the length of the settling time, mobiles can reduce network traffic and optimize routes by eliminating those broadcasts that would occur if a better route was discovered in the very near future [8].

B. Dynamic Source Routing (DSR)

DSR uses source routing rather than hop-by-hop routing, with each packet to be routed carrying in its header the complete, ordered list of nodes through which the packet must pass [6]. The key advantage of source routing is that intermediate nodes do not need to maintain up-to-date routing information in order to route the packets they forward, since the packets themselves already contain all the routing decisions. This fact, coupled with the on-demand nature of the protocol, eliminates the need for the periodic route advertisement and neighbor detection

packets present in other protocols [9]. The DSR protocol

consists of two mechanisms: route discovery and route maintenance [1]. When a mobile node has a packet to send to some destination, it first consults its route cache to determine whether it already has a route to the destination. If it has an unexpired route to the destination, it will use this route to send the packet. On the other hand, if the node does not have such a route, it initiates route discovery by

broadcasting a route requestpacket [1, 9].

This route request contains the address of the destination, along with the source node‘s address and a unique identification number. Each node receiving the packet checks whether it knows of a route to the destination. If it does not, it adds its own address to the

route record of the packet and then forwards the packet

along its outgoing links [9]. To limit the number of route requests propagated on the outgoing links of a node, a mobile only forwards the route request if the request has not yet been seen by the mobile and if the mobile‘s address

does not already appear in the route record. A route replyis

generated when the route request reaches either the destination itself or an intermediate node which contains in its route cache an unexpired route to the destination [6]. DSR uses two types of packets for route maintenance: - Route Error packet and Acknowledgements [10]. When a node encounters a fatal transmission problem at its data link layer, it generates a Route Error packet. When a node receives a route error packet, it removes the hop in error from it's route cache. All routes that contain the hop in error are truncated at that point. Acknowledgment packets are used to verify the correct operation of the route links. This also includes passive acknowledgments in which a node hears the next hop forwarding the packet along the route [4].

C. Ad Hoc On-Demand Distance Vector (AODV)

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In order to maintain routes, AODV normally requires that each node periodically transmit a HELLO message, with a default rate of once per second. Failure to receive three consecutive HELLO messages from a neighbor is taken as an indication that the link to the neighbor in question is down [8]. Alternatively, the AODV specification briefly suggests that a node may use physical layer or link layer methods to detect link breakages to nodes that it considers neighbors. When a link goes down, any upstream node that has recently forwarded packets to a

destination using that link is notified via an

UNSOLICITED ROUTE REPLY containing an infinite metric for that destination. Upon receipt of such a ROUTE REPLY, a node must acquire a new route to the destination using Route Discovery as described above [1, 15].

III. SIMULATION MODEL

We made a simulation model using NS2 simulator in order to evaluate the performances of Ad-Hoc network routing protocols. The traffic sources are Constant Bit Rate (CBR). The mobility model uses ―random waypoint model‖ in a rectangular field of 1000m x 1000m with 50 nodes. Five different quantitative metrics were used to compare the performance of routing protocols against mobility of the nodes and traffic load conditions. The performance metrics considered for evaluation of these routing protocols are as follows: throughput, packets dropped, normalized routing overhead, end-to-end delay, and optimal path length. In Table 1, we have summarized the model parameters that have been used for our experiments.

1 The traffic model:Constant bit rate (CBR) traffic sources were used. The source-destination pairs were spread randomly over the network. The packet size was fixed to 512bytes. When defining the parameters of the communication model, the transmission rate used was 4 packets per second and the network contained 10 or 20 connections. Varying the number of CBR sources equivalent to varying the transmission rate. Hence, for these simulations the sending rate was fixed at 4 packets per second.

TABLEI SIMULATION PARAMETERS

Parameter Value

Simulator NS 2.35

MAC Type 802.11

Simulation Time 300 seconds Channel Type Wireless Channel Routing Protocol DSDV, AODV, DSR Antenna Model Omnidirectional Simulation Area 1000 m x 1000 m

Traffic Type CBR

Packet Size 512 bytes

Connection Rate 4 packets/sec # of connections 10 and 20 Radio Propagation Model TwoRayGround Interface Queue Length 50

Interface Queue Type DropTail/PriQueue (DSDV and AODV)

and CMUPriQueue (DSR) Number of nodes 50

Speed 1m/s and 20 m/s

Pause Time 0, 30, 60, 120, 200, 250, 300 sec

Mobility Model Random Way point Mobility

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IV. PERFORMANCE EVALUATION

A.Performance Evaluation Metrics

1 Throughput: The number of packets received by the destination within a given time interval.

2 Packets Dropped: It occurs when one or more packets fail to reach to their destination.

3 Normalized Routing Overhead: The number of routing packets transmitted per data packet delivered at the destination.

4 End-to-End Delay:It includes all possible delays caused by buffering during route discovery, queuing delay at the interface, retransmission delays at the MAC, propagation and transfer times.

5 Optimal Path Length: The average number of hops taken by a delivered packet on its way to the destination. Optimal path length increases as the number of hops on optimal path increases.

B.Simulation Results

Figure (1-15) show the effect of mobility for DSDV, DSR and AODV protocols with respect to various performance metrics. Three scenarios were taken. First scenario was low mobility (v=1m/s) and low traffic (maximum number of connections =10), second scenario was low mobility (v=1m/s) and high traffic (maximum number of connections =20) and third scenario was high mobility (v=20m/s) and high traffic (maximum number of connections =20).

1 Throughput

Fig.1 shows the throughput in kilobits/second vs. the pause time for DSDV, AODV and DSR. The velocity (v=1m/s) and maximum number of connections =10. Fig.2 and Fig.3 shows the throughput of DSDV, AODV and DSR in kilobits/second for v=1m/s and 20m/s respectively where the maximum number of connections=20. Efficient routing protocols must have high throughput. In the network with low load traffic (cbr sources=10), DSR outperformed AODV at 1 m/s. This was due to the use of route cache and overhearing properties of DSR routing protocol. When network is small, the effect of link failures and other factors such as the hidden terminal problem and congestion is not evident. As the number of traffic sources increase, problems of congestion, hidden terminal become more influential and thus lead to throughput degradation. Referring to Figure 2, DSDV outperforms AODV and DSR at the low speed scenario (v=1m/s) and maximum number of connections (cbr=20).

As DSDV is a proactive routing protocol, paths are readily available for traffic. DSDV maintains consistent paths in the network causing a low delay. Since throughput is the ratio of the total amount of data that a receiver receives from the sender to the time it takes for the receiver to get the last packet, a low delay in the network translates into higher throughput. DSR performed poorly in these ―stressful‖ situations (high mobility, more network load). This is mainly attributed to aggressive use of caching and lack of any mechanism to expire stale routes or determine the freshness of routes when multiple choices are available. By increasing the velocity to 20 m/s AODV outperforms DSDV. DSDV uses the table-driven approach of maintaining routing information; it is not as adaptive to the route changes that occur during high mobility. In contrast, the lazy approach used by the on-demand protocol, AODV to build the routing information as and when they are created makes it more adaptive and results in better performance. From these figures, it can be concluded that DSR outperforms AODV and DSDV in smaller networks and low and speed scenario. DSDV outperforms AODV and DSR in larger networks and low speed scenario. AODV performs better in networks with relatively high number of traffic sources and higher mobility.

2 Packets Dropped

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In DSR, with stale route, it is possible that the route was not validated and so it will cause loss of packets before source node was notified that the route is invalid. In AODV, a route which was not used for a period of expire time would be deleted.

FIGURE 1:THROUGHPUT VS. PAUSE TIME (V=1M/S), MAX NUMBER OF CONNECTIONS=10

FIGURE 2:THROUGHPUT VS.PAUSE TIME (V=1M/S), MAXIMUM NUMBER OF CONNECTIONS=20

FIGURE 3:THROUGHPUT VS.PAUSE TIME (V=20M/S), MAXIMUM NUMBER OF CONNECTIONS=20

FIGURE 4:PACKETS DROPPED VS.PAUSE TIME (V=1M/S), MAXIMUM NUMBER OF CONNECTIONS=10.

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FIGURE 6:PACKETS DROPPED VS.PAUSE TIME (V=20M/S), MAXIMUM

NUMBER OF CONNECTION =20

3 Normalized Routing load

Fig.7 and Fig.8 show the normalized routing load vs.

pause time with maximum number of connections =10 and 20 respectively, at speed = 1m/s. Fig.9 shows the

normalized routing load vs. pause time with maximum

number of connections 20 and speed = 20m/s. Fig. 7 shows that in terms of routing overhead, DSR outperforms AODV and DSDV at low load traffic (10 connections) and low speed (v=1m/s). The superiority of DSR comes from the nature of its routing operation. As a reactive protocol, DSR sends routing traffic into the network only when the source has data to send thus eliminating the overhead due to unnecessary routing traffic. DSR uses source routing in its operation thereby making the source aware of the entire path the packets will flow. All intermediate nodes use cached information to relay traffic and do not send replies during route discovery. Only the destination node sends the replies to route requests. The presence of multiple routes in DSR reduces the number of route discoveries in case of link failure. These factors coupled with the absence of periodic updates in DSR, has the net effect of reducing the amount of routing traffic. In the present study the routing overhead in AODV was higher than in DSR despite both being reactive protocols. In AODV, every intermediate node sends route request replies to the source. Control overhead increases due to the multiple route replies to single route request packets. Furthermore, when a single node in the path fails, a route error message propagates to all its neighbors due to the absence of multiple paths to use as alternative routes for the traffic. This initiates a full-scale route rediscovery process thus increasing the routing overhead.

Referring to Fig.8 and Fig.9, it can be seen that in the presence of high mobility (v=20 m/s), link failures can happen very frequently. Link failures trigger new route discoveries in AODV since it has at most one route per destination in its routing table. Thus, the frequency of route discoveries in AODV is directly proportional to the number of route breaks. The reaction of DSR to link failures in comparison is mild and causes route discovery less often. The reason is the abundance of cached routes at each node. Thus, the route discovery is delayed in DSR until all cached routes fail. But with high mobility, the chance of the caches being stale is quite high in DSR. Eventually when a route discovery is initiated, the large number of replies received in response is associated with high MAC overhead and cause increased interference to data traffic. Hence, the cache staleness and high MAC overhead together result in high overhead traffic for DSR (significant degradation in performance for DSR) in high mobility scenarios. In lower mobility scenarios, DSR often performs better than AODV, because the chance of finding the route in one of the caches is much higher. Routing overload for DSDV was almost constant. This is because of its proactive nature. DSDV sends periodic updates at regular intervals independent of any route changes or not. So they offer constant routing overhead in all cases.

FIGURE 7:NORMALIZED ROUTING VS.PAUSE TIME (V=1M/S),

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MAXIMUM NUMBER OF CONNECTION=20

4 End-to-End Delay

Fig.10 and Fig.11 show end-to-end delay vs. pause time with maximum number of connections = 20, at speed = 1m/s and 20m/s respectively. Fig.12 shows the end-to-end delay vs. pause time with maximum number of connections = 20, at speed = 20m/.

As the figures show, the average end-to-end delay was less at DSDV protocol than for the DSR. DSR is an On-Demand source routing protocol, and this is the major reason for it having a higher End-to-End Delay, where route is looked only when needed and there is a route discovery mechanism happening every time and it also has to carry a large overhead each time, thus the higher delay. Although DSR maintains multiple routes to the same destination in the cache, but it lacks any mechanism to determine the freshness of a route. It also does not have any mechanism to expire the stale routes. With high mobility link breaks become more frequent and there is the chance of the cached routes becoming stale quickly. DSR, being unable to determine a fresh route, may pick up a stale route for packet delivery. Moreover, every intermediate node can extract the information before forwarding the data packet and use this information to update its own cache entries. Therefore, selecting a stale route from a particular node‘s cache may pollute the cache entries of other nodes as well. This requires DSR to initiate more route discoveries which further adds to the increasing delay. AODV on the other hand has only one route per destination in the routing table, which is constantly updated based on sequence number and DSDV has to continuously update the whole routing table periodically and when needed, which leads to a slight delay in delivery.

5 Optimal Path Length

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FIGURE 10:END-TO-END DELAY VS.PAUSE TIME (V=1M/S), MAXIMUM

NUMBER OF CONNECTIONS=10

FIGURE 11:END-TO-END DELAY VS.PAUSE TIME (V=1M/S), MAXIMUM NUMBER OF CONNECTIONS=20

FIGURE 12:END-TO-END DELAY VS.PAUSE TIME (V=20M/S),

MAXIMUM NUMBER OF CONNECTIONS=20

FIGURE 13:OPTIMAL PATH LENGTH VS.PAUSE TIME (V=1M/S),

MAXIMUM NUMBER OF CONNECTIONS =10.

MAXIMUM NUMBER OF CONNECTIONS =20

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V. CONCLUSION

At low mobility scenario (v=1m/s) and low traffic load (cbr=10) DSR performed better than DSDV and AODV in terms of throughput, packets dropped and NRL. This can be attributed to the use of source routing and route cache. However, it had high delay because DSR is an On-Demand source routing protocol, and this is the major reason for it having a higher End-to-End Delay, where route is looked only when needed and there is a route discovery mechanism happening every time and it also has to carry a large overhead each time, thus the higher delay. If the traffic load and/or the mobility increases, DSR will perform poorly. This is mainly attributed to the aggressive use of caching, and lack of any mechanism to expire stale routes or determine the freshness of routes when multiple choices are available. Aggressive caching, however, seems to help DSR at low loads and also keeps its routing load low. DSDV outperformed DSR and AODV at low speed (v=1m/s) and high load. DSDV gave the lowest normalized routing load for more than 10 connections at low and high speed. It also had low End-to-End delay almost at all scenarios because it is table driven, for it has more routes in its routing table that has already been found. Therefore, this protocol sends the packets to the desired destinations faster, with no need for the route discovery process. It also had the best optimal path compared to DSR and AODV at all the scenarios. DSDV performance is worst when mobility is high. This poor performance is because of the reason that DSDV is not on demand and it keeps only one route per destination therefore lack of alternate routes and presence of stale routes in the routing table when nodes are moving at higher rate leads to packet drops. At high mobility and high traffic load AODV performs better in throughput, PDF and packets drop. AODV finds the routes on demand. It uses routing tables, one route per destination, and destination sequence numbers, a mechanism to prevent loops and to determine freshness of routes which makes it more adaptive and result in better performance.

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