Performance Analysis of Wireless Mobile Adhoc NetworkRouting Protocols

I.VijayaTATA Consultancy Services

Kolkata, Indiaivijaya@rediffmail.com

Amiya Kumar RathDept. of Computer Science

College of Engineering, BhubaneswarBhubaneswar, India

amiyaamiya@rediffmail.com

Abstract – An ad hoc network is a collection of wireless mobile nodes dynamically forming atemporary network without the use of any existing network infrastructure or centralizedadministration. A number of routing protocols like Dynamic Source Routing (DSR), Ad Hoc On-Demand Distance Vector Routing (AODV) and Destination-Sequenced Distance-Vector (DSDV) havebeen implemented. Routing in ad hoc networks is a complex problem and a multitude of routingprotocols have been developed. This paper compares the results from four independentevaluations of the three routing protocols DSR, AODV and DSDV. DSDV show inferior performancecompared to the other two. Comparing DSR and AODV no conclusive results can be drawn sincethe different evaluations come to different conclusion.

We quantify the effect of node mobility and message length on the BER of an average multi-hop route using a recently developed communication-theoretic framework for adhoc wirelessnetworks [2]. We study the network performance such as throughput, delivery ratio, and end-to-end delay when position-based routing is used. The performance differentials are analyzedusing varying simulation time. These simulations are carried out using the ns-2 networksimulator. The results presented in this work illustrate the importance in carefullyevaluating and implementing routing protocols in an ad hoc environment.

Keywords- Performance, Analysis, Ad Hoc Network, AODV, DSR, DSDV, NS2.

I. INTRODUCTION Evaluating the performance of Mobile Adhoc Wireless Networks is thus importantbecause it allows one to determine the types of applications that can be supportedon such networks. Routing in ad hoc networks is a complex problem and a multitude ofrouting protocols have been suggested and evaluated. One reason for the large numberof protocols is that the efficiency of the protocols varies depending on mobilityand traffic pattern. Since mobile ad hoc networks is a relatively new research area,and the fact that no widespread real applications exist, relatively simple mobilityand traffic models have been used to evaluate ad hoc routing protocols. Due todifferent protocol configurations and different models and model configurationsprotocol evaluations have come to different conclusions. The network performancemetrics evaluated in these studies are usually network layer related parameters suchas packet delivery ratio, average end-to-end delay, and average hop count, andcontrol packet overhead. In this work an attempt has been made to compare theperformance of two prominent on demand reactive routing protocols and one proactive

routing protocol for MANETs: - On demand Distance Vector (AODV), Dynamic SourceRouting (DSR) and Destination Sequenced Distance Vector (DSDV) protocols. DSR andAODV is a reactive gateway discovery algorithm where a mobile device of MANETconnects by gateway only when it is needed. As per our findings the differences inthe protocol mechanics lead to significant performance differentials for both ofthese protocols. In addition, we investigate the impact of the link distance, namelythe geographic distance for a hop, on the end-to-end network throughput. This workis a comprehensive simulation study on the impact of various factors on theperformance of MANETs. It also provides guidelines for future protocol and algorithmdesign. Further DSR has performed well for the performance parameters namelydelivery ratio and routing overload while AODV performed better in terms of averagedelay and DSDV performed well providing loop free path and removed the count toinfinity problem. We demonstrate that even though DSR and AODV share similar on-demand behavior as compared to DSDV, the differences in the protocol mechanisms canlead to significant performance differentials.

II. BACKGROUND AND PRELIMINARIES

Mobility Models:The mobility pattern of nodes affects the performance of an ad hoc network [1] andpossibly the relative performance of routing protocols. For this reason it isimportant to choose a mobility model that closely resembles the mobility pattern ofthe network where the routing protocol will be used, otherwise the results will bemisleading. There are two types of mobility models used in simulations; traces andsynthetic models [1]. The advantage of a trace is that it represents an actual caseto benchmark the routing protocol against. The problem with traces is that they canbe costly and difficult to acquire, and for new applications it is not possible toget a trace. In a synthetic model the mobility of nodes are modeled, often usingsome kind of random movement. In the most commonly used synthetic mobility the nodesmove around in an open unobstructed space [3][1]. In a real-world scenario it isvery unlikely environment is obstruction free. In [3] Jardosh et al. create anenvironment model that has obstructions here nodes only may move along predeterminedpaths. Their model is still very rough, but it shows that by hanging theenvironment a routing protocol (in their case AODV) do get a different performance.Another problem with some of the more commonly used mobility models is that thestatistical properties of the initial state does not correspond to the statisticalproperties of the steady state, resulting in a settling time [14][15]. During thesettling time the statistical properties of the node states constantly changes,which means that the data collected during this time is of limited value. The steadystate properties of a model might also not be what the user desired. For thesereasons it is important to know the statistical properties of the models used and touse models that do not have a settling time. As shown by [3] and [14] the task ofcreating a representative and stable mobility model is non-trivial. Since mostmobility models used in ad hoc research have not been statistically stable and notreal-world representative further development of the synthetic mobility models areneeded to be able to properly evaluate the performance of ad hoc routing protocols.

The properties that are desirable in Ad-Hoc Routing protocols are

Distributed operation: The protocol should be distributed.It should not be dependent on acentralized controlling node. This is the case even for stationary networks. The difference is that the nodes in an ad-hoc network can enter or leave the network very easily and because of mobility the network can be partitioned.Loop free: To improve the overall performance, the routing protocol should guaranteethat the routes supplied are loop free. This avoids any waste of bandwidth or CPUconsumption.Demand based operation: To minimize the control overhead in the network and thus notwaste the network resources the protocol should be reactive. This means that theprotocol should react only when needed and that the protocol should not periodicallybroadcast control information.Security: The radio environment is especially vulnerable to impersonation attacks soto ensure the wanted behavior of the routing protocol we need some sort of securitymeasures. Authentication and encryption is the way to go and problem here lieswithin distributing the keys among the nodes in the ad-hoc network.Quality of Service Support: Some sort of Quality of service is necessary to incorporateinto the routing protocol. This helps to find what these networks will be used for.It could be for instance real time traffic support. It should be noted that none ofthe proposed protocols have all these properties, but it is necessary to rememberthat the protocols are still under development and are probably extended with morefunctionality.

III. ROUTING PROTOCOLS

Figure 1 Routing Protocols

Routing in ad hoc networks is a complex problem and much research is going on in thefield. A description of the problems and a set of routing protocols can be found in[3]. The routing protocols DSR, AODV and DSDV are often used as reference protocolswhen a new protocol shall be evaluated. To understand the characteristics of theseprotocols they are described in the sections below and their performance isevaluated in section V.

Adhoc Routing Protocols

Flat Routing Hierarchical Routing

Geographic position assisted routing

Proactive

Reactive

FSR FSLS OLSR DSDV BRF AODV DSR HSRCGSR ZRP LANMAR GeoCast LAR DREAM GPSR

A. DSR Dynamic Source Routing (DSR) [4][5][3] is a reactive routing protocol designed forad hoc networks up to 200 nodes. DSR is a source routing protocol, which means thatthe source specifies the complete route to the sink. The intermediary nodes justforward the package based on the route specified by the source. DSR maintains aroute cache, and as long as there is a route to the sink in the cache no routediscovery has to be performed. The route cache can contain multiple paths to a nodeand the choice of route to a destination is based on some selection criteria.If there is no route to the sink in the cache a route discovery has to be performed.To perform a route discovery a route request message is broadcast. When the routerequest reaches the target a route reply is returned to the source. If the links arebi-directional then the reply is sent back over the route the route requesttraveled, otherwise it is returned via a route cached in the destination or by beingpiggybacked on a route request.The destination replies to each different node that sends a route request, whichmeans that the source will be given multiple paths to the destination. When a usedlink is broken a route error message is sent back to the source and the path isinvalidated.B. AODVAd hoc On-Demand Distance Vector (AODV) Routing [6][7][3] is a reactive routingprotocol designed for ad hoc networks up to thousands of nodes. In AODV nodesmaintain traditional routing tables specifying the next hop to take to reach thedestination.If there is no information in the routing table of the source then a route requestis broadcast. A node that receives the route request and has an up-to-date path tothe destination will return it to the source and all nodes on the return path willupdate their routing tables. If no valid path is present in an intermediary nodethen the request is rebroadcasted. If a node receives multiple paths to thedestination the one with the highest utility is chosen.AODV specifies two different ways in which a link break can be detected. Either allnodes regularly broadcast a hello message to its one-hop neighbors, which makes itpossible for them to verify the link operation, or it is detected by a linksignaling mechanism when the link is used. When a link break is detected the endnodes (source and destination) are informed and it is up to them to find a new path.To reduce the route request broadcast storms the route discovery can be performedusing an expanding ring search. In an expanding ring search the route discovery areais limited by the TTL field in the IP header. A sequence of route requests areperformed with increasing TTL until the destination is found or a set limit isreached. If a stale route to the destination is available that hop count can be usedas an initial TTL limit.C. DSDVDestination Sequenced Distance Vector (DSDV) [8][3] is a table driven routingprotocol that is an enhanced version of the distributed Bellman-Ford algorithm. Asall table driven protocols each node maintains a table that contains the next hop toreach all destinations. To keep the tables up to date they are exchanged between

neighboring nodes at regular intervals or when a significant topology changes areobserved.

III. ROUTING PROTOCOL PERFORMANCEThis section summarizes and compares the results regarding the routing protocolsDSR, AODV and DSDV in the papers by Boukerche [9], Johansson et al. [10], Das et al.[11] and Broch et al. [12]. All papers except [11] compare all three routingprotocols discussed in this paper. [11] only compares AODV to DSR. [9] and [12] doeshave some additional routing protocols in their evaluations.Comparing the results in the papers directly is not possible since the testenvironments and used protocol features vary. What can be done is to see if theprotocol behavior is consistent between the papers. Common to all studies are thatthey use randomly distributed CBR sources and sinks and the random waypoint model asmobility model. CBR sources may not give results transferable to a real-worldscenario. The random waypoint model has the settling time problems discussed in [13][14][15]. From an initial linear distribution of speed and position it converges toa speed distribution where most nodes are moving slowly and the nodes a concentratedto the central part of the area (for details see [13][14][15]). This means that itis possible that none of the evaluations may be applicable to real world scenarios.Knowing these short comings the findings in the papers are described below. Therouting protocols are compared on the metrics throughput, delay and routingoverhead.A. ThroughputThe basic metric to measure throughput in is bits transmitted between source anddestination per time unit. To be able to relate this number to the desired outcomethe throughput is often presented as a ratio between transmitted packages anddelivered packages. Common to all tests is that DSDV has the poorest throughput. Thereason is that DSDV has problems dealing with mobility, and in highly mobilescenarios the throughput is often as low as 50% of the throughput in a staticsetting. The problem is that the routing table update mechanism is not fast enoughto update the routing tables when topology changes occur.When DSR and AOVC are compared there is no clear winner. According to Das et al.[11] DSR is superior for low loads with small number of nodes and AODV is better athigher loads. These conclusions are not supported by Boukerche [9]. In his tests DSRconsistently outperform AODV. But with moderate load and mobility both routingprotocols should have a throughput of at least 90%.B. DelayThe message transmission delay property is interesting for establishing theresponsiveness of applications, but there are two problems with the delaymeasurements in the source papers. First, the delay can only be computed on receivedmessages. This means that the throughput has to be acceptable before the delay isinteresting to consider. Secondly, only the average delay is reported. To be able tojudge the usefulness of the routing schemes for delay sensitive applications (likestreaming voice or video) the distribution of the delay is important to know. The papers [9][10][11] that discuss delay have different results. All papers agreeon that in general higher mobility and higher traffic load increase the delay. Das

and Johansson also show that when congestion starts to become a problem the delay atlow mobility is higher than at medium mobility. The reason for this is that severalflows are routed though the same network region resulting in congestion. Boukerchedoes not observe this behavior, which can indicate that he never loaded the networkmuch enough to get congestion. Das also observes that the correlation between end-to-end delay and number of hops is often small. The major part of the delay doescome from queuing at congested nodes. Comparing the relative merits of DSR and AODV the papers come to very differentresults. Boukerche finds that DSR has the highest average delay since thepromiscuous listening and related processing delays the packets at each hop. Dasfinds that DSR has a lower delay at low loads, but that AODV is better at highloads. Johansson finds that DSR is better than AODV. To be noted is that inJohanssons tests DSR does not used promiscuous listening.When it comes to DSDV themeasured delay is of the same magnitude as for DSR and AODV. But considering DSDV'sthroughput problems even at moderate mobility the delay is not a major concern.C. OverheadAll routing protocols generate traffic to maintain their routing tables. The twocommon ways to measure this traffic is in number of packets or number of bytes.Sometimes these numbers are related to the number of transmitted data packets orbytes. In contention based media access the cot to gain access to the mediadominates relative to the per-byte transmission cost, which means that it is moreimportant to reduce the number of routing packets than the absolute routing datasize.Comparing DSR to AODV all papers report that DSR has much lower packet overhead thanAODV. As expected the routing overhead increases as the mobility increases. At highmobility the numbers of routing packages are of the same magnitude as the datapackages for DSR. The AODV routing overhead is two to five times that of DSR underthe same conditions. One source of the AODV overhead is the regularly broadcastedhello messages. A factor reducing the SR packet count is promiscuous listening. Thelower packet overhead of DSR should translate into higher throughput for DSR sincemore channel bandwidth should be available for data packets, especially thecongestion point should be higher for DSR. But not only is the packet overheadimportant, the types of packets also affect actual bandwidth usage (see [11]. Forthe IEEE 802.11 MAC a broadcast package consumes less bandwidth than a point-to-point package. For AODV the overhead consists of a lot of broadcast packets, wherefor DSR there are more point-to-point packets. The net result is according to [11]that DSR and AODV use about the same bandwidth for routing packets. This shows thatthe lower layers affect the performance of routing protocols. The characteristics of the routing overhead of DSDV depend on its configuration asshown by Broch. In the configuration used by both Broch and Johansson the overheadis constant and independent of mobility. The reason for this is that route updatesconstantly need to be transmitted, but they are limited by a per node maximumtransmission interval. Boukerche report an extremely low overhead for DSDV.

IV. SIMULATION RESULTS AND OBSERVATIONSIn this section we present our simulation efforts to evaluate and observations thatcompare the performance of the protocols that we described previously in SectionIII.

Table -1 Simulation parameters

Protocols AODV, DSR, DSDVSimulation time

100 seconds

#of nodes 50Map size 500mx500mMax speed 20m/sMobility model

Random way point

Traffic Type

Constant bit rate (CBR)

Packet Size 512 bytesConnection rate

4pkts/sec

Pause time 0,10,20,40,100#of connections

10,20,30,40

Figure 3. Routing Packet Sent Vs. Pause Time

C. Routing OverheadAn important measure of the scalability of the protocol, and thus the network, isits routing overhead. It is defined as the total number of routing packetstransmitted over the network, expressed in bits per second or packets per second. Weevaluated that the highest amount of routing traffic is sent by AODV is followed byDSR and lastly by DSDV. The reason for incurring less overhead is that, it sends therouting traffic only when it has data to transmit, which eliminate the need to send

unnecessary routing traffic. AODV has routing overhead slightly higher than DSRbecause of multiple route replies to a single route request.

Figure 4. Packet Sent Vs. Pause Time

D. Packet Loss as a Function of Pause TimeWe observe that when the pause time is less the packet loss in DSR is more ascompared to AODV. But at higher pause time the packet loss in AODV increases this isdue to the reason that the route discovery process of AODV causes very long delaysdue to the amount of control packet transmitted which causes large number of packetsto wait in the queue. As a result of which packets in the queue get dropped whichcauses more packet loss in AODV.

Figure 5. Packet Loss Vs. Pause Time

V. CONCLUSIONWe have presented a detailed performance comparison of important routing protocolsfor mobile ad hoc wireless networks. AODV and DSR are reactive protocol while DSDVis proactive protocols. Both reactive protocols performed well in high mobility scenarios than proactive protocol. High mobilityresult in highly dynamic topology i.e. frequent route failures and changes. Bothproactive protocols fail to respond fast enough to changing topology. Routingoverhead in Proactive protocols remains almost constant while in AODV it increaseswith increase in mobility.

Both AODV and DSR use reactive approach to route discovery, but with differentmechanism. DSR uses source routing and route cache and does not depend on theirtimer base activity. On other hand AODV uses routing tables, one route perdestination, sequence number to maintain route. The general observation fromsimulation is that DSR has performed well compared to all other protocols in termsof Delivery ratio while AODV outperformed in terms of Average delay. DSR howevergenerates lower overhead than AODV while DSDV generate almost constant overhead dueproactive nature. Poor performance of DSR in respect of average delay can beaccounted to aggressive use of caching and inability to delete stale route. But itseems that caching helps DSR to maintain low overhead.High mobility results in frequent link failures and the overhead involved inupdating all the nodes with the new routing information as in DSDV is much more thanthat involved AODV and DSR, where the routes are created as and when required. Thegeneral observation from the simulation is that for application-oriented metricssuch as packet delivery fraction and delay AODV, outperforms DSR in more “stressful”situations (i.e., smaller number of nodes and lower load and/or mobility), withwidening performance gaps with increasing stress (e.g., more load, higher mobility).DSR, however, consistently generates less routing load than AODV.

VI. FUTURE SCOPE Dynamic source routing protocol is designed for use in multi-hop wireless ad hocnetworks of mobile nodes. DSR uses source routing and does not depend on timer basedactivities. So it is a fully reactive protocol which initiates a route discoveryprocess only when it has data to send. Though there are some disadvantages of thisprotocol, it is a robust protocol for use in mobile ad hoc network. Our future workswill include the modification to the basic DSR so as to reduce the routing overheadfor the performance optimization. Our work can be extended to various otherprotocols like TORA. We can also analyze performance of such protocols on theperformance parameter like standard deviation, energy consumption, etc. In this simulation study, we have not used large no of nodes and simulation time was1000s. Increasing both of them will increase computational time which was limiteddue to various reasons. Thus, in future we will try to carry out more vigoroussimulation so as to gain better understanding of such networks and subsequentlyhelps in development of new protocols or modification in existing protocols.

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