Simulation and Performance Evaluation of AODV, DSDV and DSR in TCP and UDP Environment

I.Vijaya TATA Consultancy Services (TCS)

Kolkata (West Bengal), India ivijaya@rediffmail.com

Amiya Kumar Rath College of Engineering (CEB) Bhubaneswar

Bhubaneswar(Orissa), India amiyamiya@rediffmail.com

Abstract – 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. A number of routing protocols such as Dynamic Source Routing (DSR), Ad Hoc on-Demand Distance Vector Routing (AODV) and Destination-Sequenced Distance-Vector (DSDV) have been implemented. In this paper, an attempt has been made to compare the performance of two prominent on-demand reactive routing protocols: DSR and AODV, and proactive DSDV protocol in TCP (Transmission Control Protocol) and UDP (User Datagram Protocol) environments. A simulation model with Media Access Control (MAC) is used to study interlayer interactions and their performance implications. These include the measurement of network throughput using TCP and UDP as well as the delay in transmission of packets using TCP. Correlation between the two sets of results is found to be satisfactory enough to validate the simulation process. Given this validation, based on similar simulation techniques, the investigation of a larger scale Ad-hoc network is then carried out. These simulations are carried out using NS-2 simulator. The results presented in this work illustrate the importance in carefully evaluating and implementing routing protocols in an ad hoc environment.

Keywords- Ad Hoc Network, Performance Analysis, AODV, DSR, DSDV, NS, UDP, TCP.

I. INTRODUCTION Evaluating the performance of Mobile adhoc wireless

network is important because it allows determining the types of applications that can be supported on such networks. Wireless Local Area Networks (WLANs) have enjoyed widespread acceptance over the past few years as they can provide network connectivity for mobile users. One of the main problems in successful deployment of WLANs relates to the requirement of expansion of its coverage area without investing too much in costly infrastructures. Ad-hoc wireless networks can offer appealing solutions to this problem. A wireless Ad-hoc network consists of wireless nodes communicating without the need for a centralized administration, in which all nodes potentially contribute to the routing process [1]. Wireless Ad-hoc network offers several attracting features. The first of these, relates to ease and simplicity.

Adding a node to the network depends only on its capability to reach one or more available neighboring nodes. The second is that wireless Ad-hoc networks allow the users

to overcome the geographical and location limitations. This is because all nodes in the network can provide network connectivity for their neighboring nodes as opposed to a single access point in an infrastructure mode wireless network.

In this paper, we report on collection and comparison of data that include the average throughput between nodes in the network using TCP and UDP transport protocol, and delay in packet transmission using TCP. The validation is based on comparison and analysis of the results of the physical experiments with those obtained from the simulation. Following the validation, the results for simulation of larger networks are reported. The simulation techniques can then be expanded for investigation of other important issues in Ad-hoc networks such as routing and security.

There are many routing protocols in MANET, the popular ones being AODV, DSR and DSDV. Although a lot of research work is done on individual protocols but not enough research is done on comparing these protocols under different environments such as UDP and TCP. This is essential considering the fact that these protocols behave differently or perform differently in different environments. By analyzing how a protocol performs under a certain environment, the shortcomings of the protocol can be found out and more research could be done on removing those shortcomings. Further, this research work also helps in choosing a protocol best suited to particular conditions by finding out the pros and cons of the tested protocols. The objective is to analyze, simulate and do a comparative analysis of three MANET routing protocols namely AODV, DSR and DSDV under different environments. These three protocols have different properties and based on the way they are designed, they behave differently in different environments. Therefore it becomes essential to analyze each protocol by simulating it in an ideal environment and find out how it performs, so that appropriate methodologies could be followed in the future research works to improve on the areas where a protocol is lacking.

II. BACKGROUND AND PRELIMINARIES Problems with routing in Mobile Ad-hoc Networks Asymmetric links: Most of the wired networks rely on the symmetric links which are always fixed. But this is not a case with ad-hoc networks as the nodes are mobile and constantly changing their position within network. For example, consider a MANET (Mobile Ad-hoc Network)

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where node B sends a signal to node A but this does not tell anything about the quality of the connection in the reverse direction [23]. Routing Overhead: In wireless adhoc networks, nodes often change their location within network. So, some routes are generated in the routing table which leads to unnecessary routing overhead. Interference: This is the major problem with mobile ad-hoc networks as links come and go depending on the transmission characteristics, one transmission might interfere with another one and node might overhear transmissions of other nodes and can corrupt the total transmission. Dynamic Topology: This is also the major problem with ad-hoc routing since the topology is not constant. The mobile node might move or medium characteristics might change. In ad-hoc networks, routing tables must somehow reflect these changes in topology and routing algorithms have to be adapted. For example, in a fixed network routing table updating takes place for every 30sec [24]. This updating frequency might be very low for ad-hoc networks.

III. ROUTING PROTOCOLS Figure 1 depicts broad classification of different routing protocols. The characteristics of each are described in the sub sections.

Figure 1: Routing Protocols

The routing protocols DSR, AODV and DSDV are often used as reference protocols when a new protocol shall be evaluated. To understand the characteristics of these protocols they are described in the sections below and their performance is evaluated in section IV.

A. DSR DSR [3-5] is a reactive routing protocol designed for ad hoc networks up to 200 nodes. It is a source routing protocol, in which the source specifies the complete route to the sink. The intermediary nodes just forward the packet based on the route specified by the source. It maintains a route cache, and as long as there is a route to the sink in the cache, no route discovery has to be performed. The route cache can contain multiple paths to a node and 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 broadcasted. When the route request reaches the target, a route reply is returned to the source. If the links are bi-directional then the reply is sent back over the same route where the request traveled, otherwise it is returned via a route cached in the destination or by being piggybacked on a route request. When a used link is broken a route error message is sent back to the source and the path is invalidated.

B. AODV AODV [3][6-7] is a reactive routing protocol designed for ad hoc networks up to thousands of nodes. In this, nodes maintain traditional routing tables specifying the next hop to take to reach the destination. AODV specifies two different ways in which a link break can be detected. Either all nodes regularly broadcast a ‘hello’ message to its one-hop neighbors, which makes it possible for them to verify the link operation, or it is detected by a link signaling mechanism when the link is used. When a link break is detected the end nodes (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 performed using an expanding ring search. In an expanding ring search the route discovery area is limited by the Time to live (TTL) field in the IP header. A sequence of route requests are performed with increasing TTL until the destination is found or a set limit is reached. If a state route to the destination is available that hop count can be used as an initial TTL limit.

C. DSDV DSDV [3][8] is a table driven routing protocol that is an enhanced version of the distributed Bellman-Ford algorithm. In all table driven protocols each node maintains a table that contains the next hop to reach all destinations. To keep the tables up to date they are exchanged between neighboring nodes at regular intervals or when a significant topology changes are observed.

IV. SIMULATION RESULTS AND OBSERVATIONS In this section, we present our simulation efforts to evaluate our observations that compare the performance of the protocols that we described previously in Section III in different environments. The simulations were performed under two protocols i.e. UDP and TCP as the base protocols as given in the table.

TABLE I. TRAFFIC ENVIRONMENT

Protocols AODV, DSR, DSDV Simulation time 2000 seconds

#of nodes 10-50 Map size 800mx800m Max speed 25m/s

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Mobility model Random way point Traffic Type Constant bit rate (CBR) Packet Size 512 bytes Connection rate 4pkts/sec Pause time 0, 5, 10, 15, 20, 25 #of connections 10,20,30,40

A. Throughput of Received Packets This represents the number of packets received within a given time interval. Figure 2 shows that throughput for AODV in UDP increases gradually over time increase is consistent. For DSR, that the throughput increases gradually over time but the spikes show that there is sudden increase in throughput at times which shows a lack of consistency at certain periods. For DSDV protocol, it is constant from 10 to around 25 seconds and then it jumps suddenly. Then it remains almost constant for certain time period and then it jumps again. Figure 3 shows that the throughput for AODV in TCP is high initially and then it drops suddenly, then it rises and remains almost constant for the rest of the time period. DSR depicts that the throughput rises constantly and the rise is consistent i.e. it rises in constant intervals. For DSDV throughput is very high in the initial stage and the rise in throughput is maintained throughput the time interval.

Figure 2: Throughput of Packets Received in UDP environment

Figure 3: Throughput of Packets Received in TCP environment

B. Throughput of Dropped Packets This represents the number of packets dropped within a given Time Interval.

From Figure 4 we see that the throughput of dropping packets for the AODV protocol is low. Only at a couple of times, it shows a jump in the dropping rate, but nonetheless, the overall rate of packet drop is less. Packet drop throughput for the DSR protocol is also less, even less than AODV protocol and for DSDV protocol is very high. It means that it drops packets frequently. From Figure 5 the throughput of dropping packets for the AODV protocol is pretty much high. It shows high jumps at certain places which means that the packets are frequently dropped. Packet drop is less than the AODV protocol although it also shows certain amount of packet drop at time and DSDV is very low, almost close to zero.

Figure 4: Throughput of Packets dropped in UDP environment

Figure 5: Throughput of Packets dropped in TCP environment

C. End to End Delays It represents the delay encountered between the sending and receiving of the packets. From the figure 6 we find out that there is some initial delay caused in the throughput which is probably the delay caused during the route discovery process by AODV. After that, as the throughput increases, the end to end delay also increases but becomes almost constant. DSR shows that an initial delay is introduced to start the throughput and then it drops somewhat and then it rises suddenly to very high levels and then again drops. For DSDV the end to end delay is almost zero. Only at a single point, it shows a sharp rise but overall it is negligible. Figure 7 depicts that the end to end delay increases gradually and then it drops and then shows some variation in the delay. This means that AODV does introduce some

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delay in the throughput which is possibly caused because of the route discovery process. DSR shows that there is small delay in receiving the initial packets but after that, the delay increases gradually. After that, very high delay is introduced between data packets. For DSDV the delay is less for initial some time and then it rises to high levels. Then it suddenly drops and remains almost constant.

Figure 6: End-to-End delay in UDP environment

Figure 7: End-to-End delay in TCP environment

D. Packet Delivery Fraction Packet Delivery Fraction (PDF): The ratio of the data

packets delivered to the destinations to those generated by the CBR (Constant Bit Rate) sources is known as PDF. From the figure 8 & 9, the on-demand protocols, DSR and AODV performed well delivering the greater % of the originated data. When the no. of nodes increases AODV performs better as nodes attain a stable path and become stationary. DSDV performance drops because more packets drop due to link breaks. DSR performs poorly with reduced pause time. Variation in speed of nodes has less impact on AODV protocol. DSDV produces more sent packet as it recovers from dropped packets. DSR performs less compared to the other two protocols. DSR performs well when the number of nodes is less as the load will be less. However its performance declines with increased number of nodes due to more traffic in the network. The performance of DSDV is better with more number of nodes than in comparison with the other two protocols. The performance of AODV is consistently uniform.

Figure 8: Packet delivery fraction in UDP environment

Figure 9: Packet delivery fraction in TCP environment

E. Routing Load The number of routing packets transmitted per data packet delivered at the destination. Each hop wise transmission of a routing packet is counted as one transmission. From figure 10 & 11 DSR shows significantly lower routing load than AODV, with the factor increasing with a growing number of sources. When the number of sources is low, the performance of DSR and AODV is similar regardless of mobility. With large numbers of sources, AODV starts outperforming DSR for high mobility scenarios. AODV starts outperforming DSR at a lower load with a larger number of nodes. DSR always demonstrates a lower routing load than AODV. The major contribution to AODV’s routing over-head is from route requests, while route replies constitute a large fraction of DSR’s routing overhead. Furthermore, AODV has more route requests than DSR, and the converse is true for route replies.

Figure 10: Routing Load in UDP environment

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Figure 11: Routing Load in TCP environment

V. CONCLUSION This paper work presents a detailed comparative analysis of

three MANET protocols i.e. AODV, DSR and DSDV under two different environments i.e. UDP and TCP. The concluded facts are quoted below.

TABLE II. UDP RESULTS

Comparison Results under UDP

TRP(Higher is better)

TDP(lower is better)

EED(lower is better)

PDF

AODV Most consistent Packet drop

similar to DSR

Maximum delay

introduced

90%

DSR Lack of consistency(sud

den jumps in throughput)

Least packet drop

Delay within acceptable

limits

95%

DSDV Least consistent Highest packet drop

Minimum delay

85%

TABLE III. TCP RESULTS

Comparison Results under TCP

TRP(Higher is better)

TDP(lower is better)

EED(lower is better)

PDF

AODV Lack of consistency

Highest packet drop

High delay 98%

DSR Least consistency

Packet drop

acceptable

High delay 98%

DSDV Most consistent

Least packet drop

Minimum delay

introduced

88%

VI. FUTURE SCOPE DSR uses source routing and does not depend on timer based activities. So it is a fully reactive protocol which

initiates a route discovery process only when it has data to send. Though there are some disadvantages of this protocol, it is a robust protocol for use in mobile ad hoc network. Our future works will include the modification to the basic DSR so as to reduce the routing overhead for the performance optimization. Our work can be extended to various other protocols like TORA, ZRP. We can also analyze performance of such protocols on the performance parameter like standard deviation, energy consumption, etc. In this simulation study, we have not used large no of nodes and simulation time was 1000s. Increasing both of them will increase computational time which was limited due to various reasons. Thus, in future we will carry out more vigorous simulation so as to gain better understanding of such networks and subsequently helps in development of new protocols or modification in existing protocols.

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