Mobile ad hoc networks (MANETs) consist of a collection of mobile nodes which may move freely. These nodes are dynamically self-organized into arbitrary network without any fixed infrastructure. One of the fundamental challenges in MANETs is the design of dynamic routing protocols with a good performance and less overhead. Many routing protocols have been proposed for MANETs such as Ad hoc On-demand Distance Vector Routing (AODV) and Dynamic Source Routing (DSR). These two protocols are on-demand routing protocols, and they could improve the scalability in MANETs by limiting the routing overhead when a new route is requested. However, due to the mobility of nodes in MANETs, frequent link breakages may occurs which may lead to frequent path failures and route discoveries, which can increase the overhead of routing protocols by sending the Hello packets and reduce the packet delivery ratio and increasing the end-to-end delay between the nodes. Thus, reducing the routing overhead in route discovery is a very essential problem. The conventional on demand routing protocols uses flooding to discover a route. They broadcast a Route Request (RREQ) packet to the networks, and the broad casting induces excessive redundant retransmissions of Route Request packet.
There are two types of routing protocols. They are proactive routing protocol and reactive routing protocol. Proactive routing protocol maintains fresh lists of destinations and their routes by periodically distributing routing tables throughout the network. Its advantage is the low latency and its disadvantage is high routing overhead. Reactive routing protocol finds a route on demand by flooding the network with Route Request packets. Its advantage is low overhead and its disadvantage is high latency time in route finding. The Hybrid routing protocol is the combination of the advantages of proactive and reactive routing. The routing is initially established with some proactively prospected routes and then serves the demand from additionally activated nodes through reactive flooding. Proactive routing protocols are OLSR, Reactive routing protocols such as AODV, DSR, etc.,.
The coverage area concept is used to adjust the rebroadcast probability of a node. If a mobile node is located near to a sender, which means it takes a small additional coverage area and its neighbors may receive the same broadcasting message from others, thus its rebroadcast probability will be set lower. On the contrary, if a mobile node is located in the area far from sender, which means its additional coverage area is large. So it has to be set with high rebroadcast probability. The coverage area can be estimated from the distance between sender and receiver node, and the distance can be estimated by signal strength
There are two deterministic timer-based broadcast schemes:
Dynamic Re’ector Broadcast (DRB) and Dynamic Connector Connector Broadcast (DCCB). This schemes can achieve full reachability over an idealistic lossless MAC layer, and this schemes are robustness.
Robust Broadcast Propagation (RBP) protocol in wireless network is to provide near perfect reliability for ‘ooding, and this protocol has a good ef’ciency. For broadcasting they presented a new perspective: which is not to make a single broadcast more ef’cient but to make more reliable from a single broadcast, which means by reducing the frequency of upper-layer invoking ‘ooding to improve the overall performance of ‘ooding.
It may causes the broadcast storm problem, which may leads to a considerable number of packet collisions, especially in dense networks. Solutions like probability-based, distance based, counter-based, location based and neighbor knowledge based approaches have been proposed to overcome the drawbacks of flooding. This paper proposes neighbor coverage based probabilistic rebroadcast protocol along with zone routing protocol for reducing routing overhead in MANETs. NCPR comes under a reactive routing protocol so its latency time is high. So we are adding the hybrid routing protocol (ZRP) to reduce the latency time. Hybrid routing protocol has been used to reduce the control overhead of proactive routing protocol and decrease the latency caused by route discovery in reactive routing protocol. In ZRP proactive routing protocol is Intra-Zone Routing Protocol(IARP) used inside the routing zones, reactive routing protocol is Inter-Zone Routing Protocol(IERP) used between routing zones.
Broadcasting is an effective mechanism for route discovery, but in broadcasting the routing overhead can be large, especially in high dynamic networks. The broadcasting causes large routing overhead and causes many problems such as redundant retransmissions, collisions and contentionss. Thus, optimizing the broadcasting by route discovery is an effective solution for improving the routing performance.
Zhang proposed the number of rebroadcasts can effectively optimize the broadcasting. He found that the neighbor knowledge methods performs better than the area based method and the probability based method. He implements a novel scheme to calculate the rebroadcast delay for determining forwarding order. The nodes which have more common neighbors with the previous node have the lower delay. The rebroadcast probability is composed of two parts they are additional coverage ratio and thed connectivity factor. By combining these two parts we can set a reasonable rebroadcast probability.
Kim proposed a probabilistic broadcasting based on coverage area and neighbour confirmation in mobile ad hoc networks. If a mobile node is located near to the sender, which means it takes small additional coverage and rebroadcast from this node can reach only less additional nodes, so its rebroadcast probability will be set to less value. On the other hand, if a mobile node is located far from sender, which means that the additional coverage from this node is more, its rebroadcast probability will be set to high value. The coverage area can be estimated from the distance between the sender and the receiver and the distance can be estimated by signal strength. He combines the advantages of probabilistic based and area based approach.
Sinha proposed the zone routing protocol with bidirectional link. The zone routing protocol employs a proactive (table driven) and reactive (ondemand) methods to provide scalable routing in the ad-hoc network. However, in the presence of unidirectional links when ZRP is used some routes may remain undiscovered. They propose extensions to ZRP to support its deployment when unidirectional links occurs. In particular, we propose a query enhancement mechanism that recursively builds a partial routes to a destination.
Hanashi proposed a dynamic probabilistic approach when nodes move according to the way point mobility and compare it with simple flooding AODV and fixed probabilistic scheme. Their approach dynamically set the rebroadcasting based on the number of nieghbors nodes distributed in the ad hoc network. We set the rebroadcast probability of a host according tothe number of neighbor nodes information available.
Khan proposed an angle-aware broadcasting algorithm as a contribution to address the broadcast storm problem. In this approach, rebroadcast probability is dynamically calculated, based on the angles covered by a node with respect to its neighbors, without using the latter knowledge information about the nodes or any complex calculations thereof. A dynamic angle aware probabilistic broadcasting algorithm sets the forwarding probability of a node based on the cover angle of a node with respect to its neighbors. If the covered angle is small, then the node has high retransmission probability; otherwise, the retransmission probability of a node will be low. In this scheme, the position of the sender and a node itself can be estimated by the Global Positional System or any other localization technique based on the angle of arrival or triangulation or signal strength indicators.
Mohammed proposed a new probabilistic counter-based method that significantly reduces the number of RREQ packets transmitted during route discovery operation. A new hybrid route discovery approach, known as probabilistic counter-based route discovery approach which combines the advantages of fixed probability-based and counter-based broadcast schemes to address the broadcast storm problem associated with existing on-demand routing protocols. We evaluate the new route discovery method by using AODV as it is one of the early routing protocols proposed in the literature that has been widely investigated and analyzed.