Multi-hop Ad Hoc Networks are self-organizing networks characterized by dynamically changing topology due to node mobility and time varying characteristics of the wireless channel. Routing is a crucial issue in these networks. Several routing protocols have been proposed which fall into either of these categories: proactive, reactive or hybrid routing protocols. Proactive protocols have the advantage of less route establishment latency but suffer from heavy control overhead. Since routes maintained may never be used, system resources are unnecessarily wasted making proactive approaches less efficient. The reactive protocols overcome this drawback. These incur less overhead due to their "on demand" nature; nodes maintain routing information only when it is needed. Hence reactive protocols e.g AODV, DSR etc are preferred and widely adopted. But the on-demand behavior of these approaches itself leads to another problem, e.g the "broadcast storm" problem and thus challenges their usability. In this paper we highlight limitations and operational challenges of widely adopted reactive protocols and survey different optimization approaches suggested to overcome these challenges.

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The multi-hop ad hoc networks are self organizing networks with dynamic topology. The reactive and proactive protocols are designed to handle these dynamically changing networks. Ad Hoc On-Demand Distance Vector (AODV) Routing Protocol is one such Reactive protocol that has been widely adopted in MANETs. In this protocol, routes are maintained as and when required, i.e. they operate 'On Demand'. AODV relies on 'Hello' messages to maintain local link connectivity. The hello messages are sent periodically, the period of which is defined by 'AODV hello interval. In this paper, we investigate the performance of AODV protocol by varying the hello interval. The performance is analyzed in terms of Quality of Service parameters such as throughput, End-to-end Delay and PDR. Our experimental results show that the performance of AODV is improved when hello interval is increased.

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