Qutaiba A. Razouqi Ali H. Afsari Electrical Engineering Department, Kuwait University P.O.BOX: 5969 Safat. Code No:13060 Kuwait

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1 MEP -AODV: AODV-Based MAXIMUM ENERGY PATH ROUTING IN AD HOC NETWORKS Qutaiba A. Razouqi Ali H. Afsari Electrical Engineering Department, Kuwait University P.O.BOX: 5969 Safat. Code No:13060 Kuwait ABSTRACT This paper proposes a global path energy as an additional metric for route selection for the well known routing protocol Ad Hoc On-Demand Distance Vector (AODV). The resulting protocol is referred to as MEP -AODV. The motive behind this effort is to study the effect of the added metric on improving the lifespan of the Ad-Hoc communication network and the corresponding effect on the overall network performance. INTRODUCTION Ad Hoc network is a collection of two or more devices equipped with wireless communications and networking capability. The devices the form the ad hoc network can communicate within or outside their radio range and they are selforganizing and adaptive. In proactive protocols, all the nodes in an ad hoc keep track of routes to all possible destinations. Such protocols have the advantage that communications with arbitrary destinations experience minimal initial delay. However, proactive protocols suffer the disadvantage of additional control traffic that is needed to continually update stale route entries even if the route is not being used. This will waste bandwidth resources, can cause congestion at intermediate nodes, delays, and consume more energy which will affect the network life. The other category, on-demand, or reactive, protocols are designed so that routing information is acquired only when is needed. The nodes will keep track of only the needed routes and when it is needed. On-demand protocols may use far less bandwidth and reduce the network load. The drawback is long delay caused by the process of finding a route to the destination. The basic on-demand routing protocols are designed to find one route from the source to the destination nodes. Link breakage would trigger a route discovery process. High route discovery latency and frequent route discovery attempts can affect the network performance adversely. We try to overcome these issues by adding the energy metric that would provide a path with higher energy and will survive for a longer time. In this way, the chosen communication path between the endpoints will have to meet additional constraint. In the traditional protocols, the same paths will be utilized repeatedly, but with our protocol the load on the network will be distributed and the system lifetime will be maximized since a path would be preferred on others if it has a higher total energy. For some applications, it is vital to have a strong link that can hold the traffic for the longest time. This can be achieved if the selected route has enough energy to support the communication. Ad Hoc On-Demand Distance Victor Routing The Ad Hoc On-Demand Distance-Vector (AODV) [1] routing protocol * provides quick and efficient route establishment between nodes desiring communication and AODV was designed specifically for Ad Hoc wireless networks. The initial design of AODV is based on Destination-Sequenced Distance-Vector (DSDV) routing algorithm*. AODV is essentially a combination of both DSR and DSDV. It borrows the basic on-demand mechanism of Route Discovery and Route Maintenance from DSR, plus the use of hop-byhop routing, sequence numbers, and periodic beacons from DSDV. AODV was intended to reduce unwanted broadcasts as much as possible thus reducing the load on the network. DSDV issues broadcasts to announce every change in the network connectivity. Every time that two nodes enter the communication range of each other they require change in the network topology. This requires a broadcast to the rest of the nodes in the Ad Hoc network about the new connectivity information. Similarly, when two nodes drifts out of the direct communication

2 range of each other, a broadcast-triggered updated is needed to issue this link break. With AODV, no such network-wide broadcasts are required with every topology change. In fact, if the link status does not affect ongoing communication or multicast tree maintenance, no broadcast occurs. This localizes the effect caused by local movements. In DSDV, local movements have global effects. In AODV when a distant source is trying to use a broken link it causes a global effect. In addition to reducing the number of broadcasts resulting from a link break, AODV reduces the effect of stale routes as well as the need for route maintenance for unused routes. This is achieved by discarding the expired routes that are not used. This should be done carefully because it requires timing information and sometimes it is advantageous to age routes. AODV also minimizes the number of routes between any active source and destination. In this chapter, the design and protocol details for AODV are fully detailed. AODV PROPETIES AODV is an on-demand routing protocol. It does not maintain routes for every node to every other node in the network. Whenever a route to the destination is needed, it initiates a route discovery process and the route s remains as long as they are necessary. AODV is loop free at all times (it avoids the Bellman-Ford Count to infinity problem), even while repairing broken links [Perkins+ 1999] which offers quick convergence when the ad-hoc network topology changes. This loop freedom is accomplished through the use of sequence numbers. Each node maintains its own monotonically increasing sequence number, which increases each time it learns of a topology change of its neighborhood. Beside loop freedom, the use of the sequence number assures that the most recent route is selected whenever a route discovery is initiated. In addition, each multicast group has its own sequence number, which is maintained by the multicast group leader. AODV is able to provide unicast, multicast and broadcast communication ability. Combining all three communication forms in a single protocol has numerous advantages. AODV is capable of operating on both wired and wireless media, although it is specifically designed for the wireless domain. AODV algorithm When the local connectivity of the mobile node is of interest, each mobile node can become aware of the other nodes in its neighborhood by the use of several techniques, including local broadcasts known as hello messages. The routing tables of the nodes within the neighborhood are organized to optimize response time to local movements and provide quick response time for requests for establishment of new routes AODV uses a broadcast route discovery mechanism as is also used (with modifications) in the Dynamic Source Routing (DSR) algorithm. Instead of source routing, however, AODV relies on dynamically establishing route table entries at intermediate nodes. This difference pays off in networks with many nodes, where a larger overhead is incurred by carrying source routes in each data packet. To maintain the most recent routing information between nodes, the same concept of destination sequence numbers from DSDV is used. Unlike in DSDV, however, each ad-hoc node maintains a monotonically increasing sequence number counter which is used to supersede stale cached routes. The combination of these techniques yields an algorithm that uses bandwidth efficiently (by minimizing the network load for control and data traffic), is responsive to changes in topology, and ensures loop-free routing. Path Discovery The Path Discovery process is initiated whenever a source node needs to communicate with another node for which it has no routing information in its table. Every node maintains two separate counters: a node sequence number and a broadcast id. The source node initiates path discovery by broadcasting a route request (RREQ) packet to its neighbors. The RREQ contains the following fields: Source address Source sequence number Broadcast id Destination address Destination sequence number Hop count The pair < source address; broadcast id > uniquely identifies a RREQ. Broadcast id is incremented whenever the source issues a new RREQ. Each neighbor either satisfies the RREQ by sending a route reply (RREP) back to the source, or rebroadcasts the RREQ to its own

3 neighbors after increasing the hop count. Notice that a node may receive multiple copies of the same route broadcast packet from various neighbors. When an intermediate node receives a RREQ, if it has already received a RREQ with the same broadcast id and source address, it drops the redundant RREQ and does not rebroadcast it. Routes are maintained as follows. If a source node moves, it is able to reinitiate the route discovery protocol to find a new route to the destination. If a node along the route moves, its upstream neighbor notices the move and propagates a link failure notification message (an RREP with infinite metric) to each of its active upstream neighbors to inform them of the erasure of that part of the route. These nodes in turn propagate the link failure notification to their upstream neighbors, and so on until the source node is reached. The source node may then choose to reinitiate route discovery for that destination if a route is still desired. will be dropped if it is the source node or it has already heard this request before. So accepts only an earlier request packet and discards other duplicate requests. Receiving RREQ: 1. if ( (source addr, broacast ID) in request buffer ){ 2. discard request -- already heard and proccessed 3. } else { 4. add (source addr, broadcast ID) to request buffer 5. } We added an exception when the receiving node is the destination, then it accepts duplicate requests from different paths. PROPOSED MODIFICATION Without energy consideration, any routing protocol can suffer fast disruption of the network in the presence of concentrated traffic pattern. In the case of AODV, the first received rout request packet at the destination is the shortest path which will be used continuously. Figure 2. Route selection in the modified code. The path SX1-Y1-D is the selected path because it has a higher energy level. Figure 1. AODV condition checked when packet is received. rt represents the routing table and rrp is the route request packet. Sequence numbers in AODV insures loop freedom. Every node maintains a monotonically increasing sequence number for itself. It also maintains the highest known sequence numbers for each destination in the routing table (called destination sequence numbers ). The sequence number determines the freshness of the routing information. The route with the shortest hop count will be selected. This route may contain a low energy node that is on the verge of failure. We decided to add the cumulative energy level for all the nodes in the path to the route request packet. The total path energy level will be added as a third condition when selecting the route. When a node receives a route request packet, it As shown in figure 2, the path with the higher energy level will be selected when the two routes have the same number of hops. PERFORMANCE COMPARISION Three important performance metrics evaluated: are Packet delivery fraction: The ratio of the data packets delivered to the destinations to those generated by the CBR sources. Average end-to-end delay of data packets: This includes all possible delays caused by buffering during route discovery latency, queuing at the interface queue, retransmission

4 delays at the MAC, and propagation and transfer times. Normalized 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. RESULTS The simulation is conducted for 12 nodes. There are 5 active source-destination connections between the 12 nodes. A constant bit rate source (CBR) with sending rate of 4 bits/s and channel bandwidth of 0.1 Mb. The only difference between this manually created traffic and the traffic generated by the code provided by ns2 (cbgen) is that the source stops transmitting for a period then retransmits to the same destination node. We did this to provide a variation in the nodes energy levels. The simulations stop after 600 s. Figure 4. Normalized routing load vs. pause time Figure 5. Average Packet Delay vs. pause time The results show that our modified code performs better that the original AODV at high pause times (between 400 and 550 seconds). At these pause times our modified code has a lower routing load, lower delay, and better packet delivery fraction although it s performance degrades at stationary state. Figure 3. Packet delivery fraction vs. pause time CONCLUSIONS The proposed routing criterion is certainly not the ultimate solution to improve the robustness of the existing AODV protocol neither improve the network load distribution and power management. We will be pursuing our research in our future work to combine our route selection method with the multipath AODV developed by Marina [11]. We are studying also how we can use the energy information to determine route freshness beside its use in the route selection.

5 REFERENCES [1] Perkins, C., Royer, E., Ad-Hoc On-Demand Distance Vector Routing, Proc. 2nd IEEE Wksp. Mobile Comp. Sys. and Apps., Feb. 1999, pp [2] Broch, J., Maltz, D., et al. A performance comparison of multihop wireless ad hoc network routing protocols, Proc. of MOBICOM, 1998, pp [3]Samir Das, Charles E. Perkins, Elizabeth M. Royer, Mahesh K. Markina Performance comparison of two on-demand routing protocols for ad hoc networks. IEEE Personal Communications, , [4] Brown, T.X, Doshi, S., Zhang, Q., Optimal power aware routing in a wireless ad hoc network, IEEE LANMAN 2001 Workshop Proceedings, pp [13] Bor-rong Chen, Hwa Chang: Mobility Impact on Energy Conservation of Ad Hoc Routing Protocols [14] Juan-Carlos Cano and Pietro Manzoni. A Performance Comparison of Energy Consumption for Mobile Ad-Hoc Network Routing Protocols. Proceedings of the 8th International Symposium on Modeling, Analysis and Simulation of Computer and Telecommunication Systems, 2000, pages [15] Wei Yu, Jangwon Lee: DSR-based Energy - aware Routing Protocols in Ad Hoc networks. Proceedings of the International Conference on Wireless Networks (ICWN), Jun [16] Sally Floyd, Vern Paxson: "Difficulties in Simulating the Internet" [5] Fall, K., Varadhan, K., The ns Manual, (formerly ns Notes and Documentation), The VINT Project: A collaboration between researchers at UC Berkeley, LBL, USC/ISI and Xerox PARC [6] Johnson, D., Maltz, D., Dynamic Source Routing in Ad Hoc Wireless Networks, Mobile Computing, Chapter 5, pp , Kluwer Academic Publishers, [7] Maltz, D., Broch, J., Jetcheva, J., Johnson, D. The Effects of On-Demand Behavior in Routing Protocols for Multi-Hop Wireless Ad Hoc Networks, IEEE JSAC, August 1999, Volume 17, Number 8, pp [8] Veena Venugopal, Radim Barto, Michael J. Carter, Sai S. Mupparapu Improvement of Robustness for Ad Hoc Networks Through Energy -Aware Routing [9] Douglas S. J. De Couto, Daniel Aguayo, John Bicket, Robert Morris A High Throughput Path Metric for MultiHop Wireless Routing [10] Royer, E., Toh, C., A Review of Current Routing Protocols for Ad Hoc Mobile Wireless Networks, IEEE Personal Communications, April 1999, pp [11] Mahesh K. Marina, Samir Ranjan Das: Ad hoc on-demand multipath distance vector routing. Mobile Computing and Communications Review 6(3): (2002) [12] M. Yuksel, B. Sikdar, K.S. Vastola and B.K. Szymanski Workload generation for ns simulations of wide area networks and the Internet Proc. Communication Networks and Distributed Systems Modeling and Simulation, SCS, San Diego, CA, 2000, pp