Performance Evaluation of Routing Strategies in MANETs

Transcription

1 Performance Evaluation of Routing Strategies in MANETs MUHAMMAD SHABBIR Mirpur, Azad Kashmir PAKISTAN Abstract: - Ad hoc networks are gaining increasing popularity in recent years because of their ease of deployment. No wired base station or infrastructure is supported, and each host communicates one another via packet radios. In ad hoc networks, routing protocols are challenged with establishing and maintaining multihop routes in the face of mobility, bandwidth limitation and power constraints. In this paper, the distance vector based Wireless Routing Protocol () and Adaptive Distance Vector protocol (), the link state based reactive protocol Fisheye State Routing (), the on-demand routing protocol Dynamic Source Routing () and Associativity Based Routing protocol (), and the location based reactive protocol Location-Aided Routing protocol () are simulated using OPNET Modeler and compared under various network scenarios (e.g., different mobility patterns, mobility rates, traffic patterns, etc). Our study shows that overall, all protocols performed much better with the group mobility model than with the random waypoint model. and, especially, are the main beneficiaries of the group mobility model. Each protocol s performance degraded as mobility rates increased. On-demand protocols were highly effective and efficient in most of our scenarios. Extra delay in acquiring routes, though, makes them less attractive in delivering real-time traffic. further improved an on-demand protocol by using location information, but produced more overhead to exchange location information. Key-Words: - MANET,,,,,, 1 Introduction A Mobile Ad Hoc Network (MANET) is an autonomous system of functionally equivalent mobile nodes, which must be able to communicate while moving, without any kind of wired infrastructure. These networks are found very appropriate for an environment where either the infrastructure is lost or where deploy an infrastructure is not very cost effective. As the necessity of exchanging and sharing data increases in our daily life, users demand ubiquitous, easy connectivity, and fast networks whether they are at work, at home, or on the move. Moreover, the mobile users require connectivity of all their personal electronic devices (PEDs) in an ad hoc manner. The network that provides connectivity in an ad hoc manner is referred to as Mobile Ad Hoc Network (MANET). However, MANETs are not only limited to civilian use but are also used in disaster recovery (such as fire, flood, and earthquake), law enforcement (such as crowd control, search, and rescue), and tactical communications (such as soldiers coordinating moves in a battlefield) [1]. Thus research in the area of mobile ad hoc networking has received wide interest. The entire life-cycle of MANETs can be classified as: First, Second, and Third Generation mobile ad-hoc networks. The ad hoc networks of these days are considered to be the third generation. The first generation called the PRNET (Packet Radio Networks) was emerged in PRNET a kind of distance-vector based routing, in combination of ALOHA (Arial Locations of Hazardous Atmospheres) and CSMA (Carrier Sense Multiple Access) approaches for medium access control were used on experimental basis to provide diverse networking capabilities in a combat situation. In 198s the second generation of MANETs comes into being by further improvement in ad hoc networks and implementation as a part of the SURAN (Survivable Adaptive Radio Networks) program. A packetswitched network provided the mobile battlefield an infrastructure less situation. The SURAN program was proved to be beneficial in improvement of the radios performance by making them smaller, cheaper, ISSN: ISBN:

2 and pliant to electronic attacks. The thought of commercial MANETs inwards in 199s, with laptop/notebook computers. In the same days, the suggestion of a collection of mobile nodes was proposed at some research meetings/conferences [2]. The research community had started to look into the prospect of deploying ad-hoc networks in other areas of application after adoption of the term ad hoc networks by the IEEE subcommittee. In the meantime, work was going on to progress the previously built ad-hoc networks. Some of the outcomes of these efforts are GloMo (Global Mobile Information Systems) and the NTDR (Near-term Digital Radio). The GloMo provided an office environment with Ethernet-type multimedia connectivity anytime and anywhere in handheld devices. The only existent non-prototypical ad-hoc network that is in use today is NTDR. It is selforganized into a two-tier network using clustering and link-state routing. Development of diverse channel access approaches now in the CSMA/CA and TDMA molds, and some other routing and topology control mechanisms were some of the other inventions of that time [3]. Later on to standardize routing protocols for MANETs, the MANET working group within the (IETF) Internet Engineer Task Force was created in mid 199s. The invention of reactive and proactive routing protocols was the development of routing within the working group and the larger community. Shortly, a medium access protocol that was based on collision avoidance and tolerated hidden terminals, making it usable for building MANET prototypes out of laptops/notebooks and PCMCIA cards was chosen a standard by IEEE subcommittee. Some other ad-hoc network standards that benefited ad-hoc networking were Bluetooth and HYPERLAN [2]. 2 MANET Routing Protocols Routing protocols proposed for wireless mobile ad hoc networks can be generally categorized by the routing strategy. First, there are protocols that are distance vector based. Pure distance vector algorithms (e.g., Distributed Bellman-Ford [4], Routing Internet Protocol (RIP) [5], etc.) do not perform well in mobile networks because of slow convergence and count-toinfinity problem [6]. Thus, newly proposed protocols modify and enhance the distance vector algorithm. Protocols of this type include Wireless Routing Protocol () [7], Destination Sequence Distance Vector (DSDV) [7] and Adaptive Distance Vector () [9] routing protocol. Second, there are protocols that are based on link state algorithm. Protocols such as Fisheye State Routing ()7], and Optimized Link State Routing (OLSR) [7] are typical link state protocols. Third, the protocols that are only proposed for ad hoc networks are on-demand routing. These routing protocols do not maintain route to each destination of the network on a continual basis. Instead, routes are established on demand by the source. When a route is needed by the source, it floods a route request packet to construct a route. Upon receiving route request, the destination selects the best route based on route selection algorithm. Route reply packet is then sent back to the source via the newly chosen route. In ondemand routing protocols, control traffic overhead is greatly reduced since no periodic exchange of route tables are required. Typical on demand routing protocols are Dynamic Source Routing () [7], Ad-Hoc On Demand Distance Vector (AODV) 7] routing, and Associative-Based Routing () [7]. Fourth, with the arrival of Global Positioning System (GPS) [8], protocols making use of node location information while building routes have been proposed recently. With the knowledge of node position, routing can be more effective at the cost of overhead required to exchange location information. Routing protocols that require GPS are Location-Aided Routing () [7], Distance Routing Effect Algorithm for Mobility (DREAM) [9], and Greedy Perimeter Stateless Routing (GPSR) [1]. 3 Performance Evaluation In this paper, performance evaluation of protocols from different classes under different network scenarios (i.e., mobility rates and mobility patterns etc) is presented. The OPNET Modeler a wireless network simulation platform is used to simulate the protocols. The results achieved helps us to study advantages and disadvantages of each protocol studied. 3.1 Simulation Model A network of 4 mobile nodes placed randomly within a 6x6 meter area with the propagation ISSN: ISBN:

3 range of radio interface for each node 2 meters and 2Mb/s channel capacity without network partitions is modeled. For each scenario, multiple runs with different seed numbers were conducted and collected data was averaged over those runs. For our experiments, a free space propagation model [11] with a threshold cutoff was chosen. The power of signal attenuates as 1/d 2 in free space model, where d is the distance between radios. Radio capture effect is taken into account. In the radio capture phenomenon the arriving signal is received if the capture ratio (the minimum ratio of an arriving packet s signal strength relative to those of other colliding packets) [11] is grater than the predefined threshold value, while other interfering packets are dropped. In our experiments we use the IEEE protocol with Distributed Coordination Function (DCF) [12] as the MAC layer. Under independent ad hoc configuration wireless channel is shared by mobiles using the basic access method DCF. Carrier Sense Multiple Access/ Collision Avoidance (CSMA/CA) with acknowledgments is used as the access scheme. For channel reservation, virtual carrier sense and Request to Send/Clear to Send (RTS/CTS) control frames for unicast may be allowed to nodes. If the packets are larger than a given threshold fragmentation of packets is allowed. However, fragmentation was not used in our simulations as data packets are small. The physical carrier sense is augmented by the virtual carrier sense in determining when mobile nodes recognize that the medium is busy by setting timers based upon the reservations in RTS/CTS packets. In the presence of high bit error and loss rates; fragmentation is helpful as it reduces the size of the data units that need to be retransmitted. To simulate a constant bit rate source, a traffic generator was developed with a data pay load of 512 bytes. We have chosen this value because smaller payload sizes penalize protocols that append source routes to each data packet. Five data sessions with randomly selected sources and destinations were simulated. Each source transmits adapt packets at a rate between.5 packet/sec, up to 5 packet/sec. Two different mobility patterns; random waypoint model [13] and the group mobility model were implemented. The implementation of Random Waypoint Model is as follows: each mobile node randomly selects one location as the destination and travels toward this destination with constant velocity chosen uniformly and randomly from (, V max ), where V max is the maximum allowable velocity for each mobile node. The node stops for a duration defined by the parameter T pause (pause time). After the pause time, the node again chooses another random destination and move toward it. This process is repeated again and again until the simulation completes. The velocity and direction of a node are chosen independently of the other nodes. In our simulations we have chosen Tpause= 1 seconds and mobility speed varies from km/hr to 7 km/hr. Note that the stationary period is not considered in computing node speed. Group mobility model is used in situations when hosts in an ad hoc network form groups and nodes in the groups are moving in a similar manner. This kind of mobility is called as group mobility. For our simulations of group mobility model, we divide our network into four groups and each group contains 1 nodes. Nodes in the same group are placed close to each other. Each group may move differently from others but nodes within a group move with a same speed and in a similar direction. Movement of each group and each node in a group can be characterized as Exponentially Correlated Random Mobility (ECRM) [14]. 4 Simulation Results 4.1 Results of Random Waypoint Model Packet Delivery Ratio Packet delivery ratio is defined as the ratio of data packets successfully delivered to the destinations and data packets originated by the sources. The effectiveness of a routing protocol is indicated by packet delivery ratio. Over all,, and routing protocols have very high packet delivery ratios, especially when subject to comparatively low mobility. Slight performance degradation is observed with mobility. Route taken by Route Request may already be broken when the source sends data or even when Route Replies are being returned back to the source in highly mobile situations. It is found that, the performance degradation at high mobility speed is due to the delay resulting from discovering routes. Although, is ISSN: ISBN:

4 an improvement of basic but does not perform much better than. Since, has several optimization features that are not implemented in. Another, factor is that, when nodes moves at high speed the location information used by may become out-of-date. Packet Delivery Ratio Fig.1: Packet Deliver Ratio as function of mobility speed When compared to other protocols, and showed less effectiveness especially at high mobility rates. Due to faster movement of nodes link connectivity changes more often which causes triggering of more update messages. An acknowledgement is required to send back by the neighborhood nodes for each triggered update, and this adds to control overhead. Many changes required being adsorbed and propagated; temporary loops may do exist and the network view converged slowly. An enormous amount of packets generated by triggered updates, acknowledgements, and loops, contributed towards collisions, congestion, and packet drops. was found sensitive to mobility. In update messages are time-triggered only, not event-triggered. As mobility speed increases, routes to remote destinations become less accurate; consequently some of the link state information maintained in route tables became vague. By shortening periodic update interval, this problem may be resolved, but at the cost of excessive routing overhead. It is seen from the Figure 1 that all protocols perform well under low mobility rates, but as, the mobility speed increases they become less effective Hop Distance Hop distance is the average number of hops traveled by data packets that reached their destinations successfully. Hop distance is closely related to the packet delivery ratio in highly mobile situation when links changes frequently, because different routing protocols give different packet delivery ratios. So, one might not confused that a low hop count indicates effectiveness of route selection. This might true only in the situations when different routing protocols have the same packet delivery ratio. Therefore, higher the packet delivery ratio, the higher the hop distance. Low hop distance means that most of the data packets are intended for delivery to nearby nodes and packets sent to remote hosts are likely dropped. Thus, the information about the survivability of the protocols is provided by the hop count. Average Hop Count Mobility Speed Fig. 2: Hop Count as a function of Mobility Speed Figure 2 shows, that the protocols that delivered more data packets as was shown in Figure 1 have higher average hop distance. Grater the distance between source and destination, grater will be the number of intermediate nodes that data packets need to visit. If the packets are required to visit many links, the probability of a packet being dropped becomes grater, particularly if network topology changes frequently. Therefore, more data packets may be drooped, if routing protocol cannot handle topology changes rapidly. So the effectiveness of protocols degraded Number of Total Packets Transmitted per Data Packets Delivered It is the measure of each data packet transmitted. The packets that are eventually drooped and retransmitted by intermediate nodes are included in this measure. This measure can be viewed as the efficiency of delivering data [15], because this figure is divided by the number of packets delivered to the destinations. ISSN: ISBN:

5 Figure 3 shows the average number of data and control packets transmitted per data packet delivered. Since, most link layer protocols are contention based; therefore, this measure is particularly significant in ad hoc networks. As compared to other protocols, and show much lower values. has less packets transmitted than and. Even though the difference is very small, this difference is due to limiting the propagation of Route Request using location information. Average No. of Total Packets Transmitted/Data Packets Deliverd Fig.3: Number of Total Packets transmitted/data Packets Delivered as a function of Mobility Speed 4.2 Results of Group Mobility Model Packet Deliver Ratio The packet delivery ratio of each protocol in the group mobility model is shown in Figure 4. Packet Delivery Ratio Fig. 4: Packet Delivery Ratio as a function of group mobility speed As compared to the random waypoint model all protocols are able to deliver more data packets successfully. This can be observed from the vertical scales of Figure 1 and Figure 4. In the group mobility model there are relatively few link changes because nodes in the same group move similarly. Route breaks occurred much less frequent even in highly mobile situations as compared to the random waypoint model. The network view converges more quickly because of few update packets are sent. This shows a spectacular improvement in. Under the group mobility model the most improved protocol is. Average No. of Total Packets Transmitted/Data Packets Delivered Fig. 5: Number of Total Packets Transmitted per Data Packets Delivered as a function of Group Mobility Speed Number of Total Packets Transmitted per Data Packets Delivered Figure 5 shows the average number of total packets transmitted per data packet delivered as a function of group mobility speed. As compared to the random waypoint model this measure also improved. The efficiencies are enhanced accordingly because protocols delivered more data. 5 Conclusion Performance evaluation of six routing protocols (,,,,, and ) representing different routing categories was conducted. Many different scenarios were considered and simulations were run. It was found that each protocol showed capability in different scenarios. It was found that, in general, with the group mobility model all protocols performed much better as compared to the random waypoint model. The main beneficiaries of group mobility model were the and. The results showed that performance of each protocol degraded with increased mobility rates. ISSN: ISBN:

6 In most of our scenarios we found on-demand protocols extremely effective and efficient. However, on-demand protocols are less attractive in delivering real-time traffic because of extra delay in acquiring routes. By the use of location information further improved an on-demand protocol. However, more over head is produced in exchanging location information. For different network scenarios each protocol has its advantages and disadvantages. Therefore, no one can easily determine a single routing strategy, which is best for all the network scenarios. References: [1]. H. Xiaoyan, M. Gerla, Y. Yunjung, X. Kaixin, and T. J. Kwon, Scalable Ad Hoc Routing in Large, Dense Wireless Networks using clustering and Landmark, 22 IEEE International Conference on Communications, vol. 5, pp , April 22. [2]. Kavita Taneja and R. B. Patel, Mobile Ad hoc Networks: Challenges and Future, Proceedings of COIT 27, National Conference on Challenges and Opportunities in Information Technology, Mandi Gobindgarh, India, pp [3]. R. Ramamathan and J. Redi, A Brief Overview of Ad Hoc Networks: Challenges and Directions, IEEE Communication Magazine, vol. 4, issue 5, May 22, pp [4]. Dimitri P. Bertsekas and Robert G. Gallager, Data Networks, Prentice Hall, Englewood Cliffs, [5]. G. Malkin, RIP version 2 Carrying Additional Information, Internet Draft, draft-ietf-ripv2- protocol-v2-5.txt, June [6]. Andrew S. Tanenbaum, Computer Networks, 4 th Edition, Prentice Hall, August 22. [7]. Roberto Beraldi and Roberto Baldoni, The Unicast Routing Techniques for Mobile Ad hoc Networks in The Handbook of Ad Hoc Wireless Networks, edited by M. Ilyas, CRC Press, pp [8]. E.D. Kaplan (editor), Understanding the GPS: principles and Applications, Artech House, Boston, MA, February [9]. Jorg Widmer, Martin Mauve, Hannes Hartenstein and Holger FuBler, Position-Based Routing in Ad Hoc Wireless Networks in The Handbook of Wireless Ad Hoc Networks, edited by M. Ilyas, CRC Press, pp [1]. Yu-Chee Tseng and Chih-Sun Hsu, Location- Aware Routing and Applications of Mobile Ad Hoc Networks in the Handbook of Wireless Ad Hoc Networks, edited by M. Ilyas, CRC Press, pp [11]. T.S. Rappaport, Wireless Communications: Principles and Practice, Prentice Hall, December 31, 21 [12]. IEEE Computer Society LAN MAN Standards Committee, Wireless LAN Medium Access Protocol (MAC) and Physical Layer (PHY) Specification, IEEE Std The Institute of Electrical and Electronics Engineers, New York, NY, [13]. J. Broch, D.A. Maltz, D.B. Johnson, Y.-C. Hu, and J. Jetcheva, A Performance Comparison of Muti-Hop Wireless Ad Hoc Network Routing Protocols, Proceedings of the ACM/IEEE International Conference on Mobile Computing and Networking (MOBICOM), Dallas, TX, October 1998, pp [14]. R. Ramanathan and M. Steenstrup, Hierarchically-Organized, Multihop Mobile Wireless Networks for Quality-of-Service Support, ACM/Baltzer Mobile Networks and Applications, special issue on Mobile Multimedia Communications, vol. 3, no. 1, June 1998, pp [15]. M.S. Corson and J. Macker, Mobile Ad Hoc Networking (MANET): Routing Protocol Performance Issues and Evaluation Considerations, Request for Comments 251, Internet Engineering Task Force, January ISSN: ISBN: