The term MANET (Mobile Adhoc Network) refers to a multihop packet based wireless network composed of a set of mobile nodes that can communicate and move at the same time , without using any kind of fixed wired infrastructure. MANET are actually self organizing and adaptive networks that can be formed and deformed on-the-fly without the need of any centralized administration.

As for other packet data networks, one –to-one communication in a MANET is achieved by unicast routing each single packet. Routing in MANET is challenging due to the constraints existing on the transmission bandwidth battery power and CPU time and the requirement to cope with the frequent topological changes resulting from the mobility of the nodes. Nodes of a MANET cooperate in the task of routing packets to destination nodes since each node of the network is able to communicate only with those nodes located within its transmission radius R, while the source and destination nodes can be located at a distance much higher than R.

A first attempt to cope with the mobility is to use the specific techniques aimed to tailoring the conventional routing protocols to the mobile environment while preserving their nature. For this reason the protocol designed around such techniques are referred to as table-driven or proactive protocols. To guarantee that routing tables are up to date and reflect the actual network topology, nodes running a protocol continuously exchange route updates and re calculate paths to all possible destinations. The main advantage of the proactive protocols is that a route is immediately available when is needed for data transmissions. However if The user traffic is not generated, and then resources are wasted due the proactive route update mechanism.

In this paper, we address the problem designing a proactive protocol scheme that does not rely on any timer-based mechanism. This scheme guarantees that valid cached routes are never removed while stale routes are removed aggressively .This proactive caching scheme has been embedded in the Zone Routing Protocol (ZRP) framework.



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