International Journal of Science and Research (IJSR), India Online ISSN: 2319-7064 Volume 2 Issue 5, May 2013 www.ijsr.net A Novel TAB Based Preemptive Multi-Hop Local Repair Algorithm for AODV in MANET Deepika Patil 1 , Nitika Vats Doohan 2 1 Dept of CSE (PG Research Scholar), SDBCT Indore, M.P., India 2 Dept of CSE (H.O.D), SDBCT Indore, (M.P), India Abstract: Maintaining the routing information for an infrastructure less network of MANET is considered as a complicated task. So many protocols deals with this routing updates like AODV, DSR, and TORA. During this route construction sometimes the route failure occurs & route repairing mechanism has to be initiated whenever it is required. Now this failed route has to be replaced before the loss of data. Considering AODV there are two approaches which deal with this link breakage. Link breaks between the routes can be handled either by reformation of new shortest route from the source to destination (Complete Source Repair), or intermediate route (Partial Local Route Repair) is formed. One of the key challenges in this context is that which one of the two is best and when to apply which of the two route repair strategies. In existing algorithm standard AODV uses a fixed hop count based threshold as a basis for deciding when to invoke Local Repair or Source Repair in case of a link break. The problem arises with this type of repairing mechanism is that the network is not clear that at which time what algorithms needs to be applied. So some condition has to be identified on the basis of which the decision can be taken. Also the decision must be pre-emptive so that the loss of data can be avoided before occurrence. This work proposes a novel Threshold Alarm Based Preemptive Route Repair Algorithm (TAB-PRRA) for Multi-Hop Local repair in AODV. It focuses on measuring those parameters which provides prior information (Preemptive) of link failure before its occurrence and also if the link break occurs that the network must know the time to start the route discovery. Keywords: MANET, AODV, TAB (Threshold Alarm Based), PRRA (Preemptive Route Repair Algorithm), RREQ, RREP. 1. Introduction Mobile ad hoc network (MANET) is the most innovative and challenging area of wireless networking. MANET is an autonomous collection of mobile users that communicate over relatively band width constrained wireless links. Some situations in which user-required infrastructure is not available, cannot be installed, or cannot be installed in time in a given geographic area. In these situations, mobile ad hoc network provides the needed connectivity and network services. Routing in MANET is a Dynamic Optimization Problem as the search space changes over time. The routing policy is defined as the rule that specifies what node to take next at each decision node to reach the destination node. Due to the time varying nature of the topology of the networks, traditional routing techniques such as distance-vector and link-state algorithms that are used in fixed networks, cannot be directly applied to mobile ad hoc networks. The constraints of MANETs demand the need of specialized routing algorithms that can work in a decentralized and self- organizing way. The routing protocol of a MANET must dynamically adapt to the variations in the network topology. The routing scheme in a MANET can be classified into two major categories – Proactive and Reactive [1]. The proactive or table driven routing protocols maintain routes between all node pairs all the time. It uses periodic broadcast advertisements to keep routing table up-to-date. This approach suffers from problems like increased overhead, reduced scalability and lack of flexibility to respond to dynamic changes. The reactive or on-demand approach is event driven and the routing information is exchanged only when the demand arises. The routing is initiated by the source. 2. Background With changing technology mobile devices getting smaller, cheaper, more convenient, and more powerful, they also run more applications and network services. All of these factors are fueling the explosive growth of the mobile computing equipment market seen today. New alternative ways to deliver connectivity have been gaining increased attention in recent years. These are focused around having mobile devices within the transmission range connect to each other through automatic configuration, setting up an ad hoc mobile network that is both flexible and powerful. By this way, mobile nodes communicate with each other and receive Internet services through an Internet gateway node, effectively extending both network and Internet services to non infrastructure [15, 16]. 2.1 Ad hoc On-Demand Distance Vector Routing AODV is an on-demand, single path, loop-free distance vector protocol [2]. It combines the on-demand route discovery mechanism in DSR with the concept of destination sequence numbers from DSDV. However, unlike DSR which uses source routing, AODV takes a hop-by-hop routing approach. Below we give an overview of some key features of the AODV protocol required for the development of AOMDV in the following section. 2.2 Route Discovery and Route Maintenance In on-demand protocols, route discovery procedure is used by nodes to obtain routes on an ‘as needed’ basis. In AODV, route discovery works as follows. Whenever a traffic source needs a route to a destination, it initiates a route discovery by flooding a route request (RREQ) for the destination in the network and then waits for a route reply (RREP) [3]. When an intermediate node receives the first copy of a RREQ 279