A Survey on Investigating the Need for Intelligent Power-Aware Load Balanced Routing Protocols for Handling Critical Links in MANETs <s> AODV. <s> This paper presents the expected transmission count metric (ETX), which finds high-throughput paths on multi-hop wireless networks. ETX minimizes the expected total number of packet transmissions (including retransmissions) required to successfully deliver a packet to the ultimate destination. The ETX metric incorporates the effects of link loss ratios, asymmetry in the loss ratios between the two directions of each link, and interference among the successive links of a path. In contrast, the minimum hop-count metric chooses arbitrarily among the different paths of the same minimum length, regardless of the often large differences in throughput among those paths, and ignoring the possibility that a longer path might offer higher throughput.This paper describes the design and implementation of ETX as a metric for the DSDV and DSR routing protocols, as well as modifications to DSDV and DSR which allow them to use ETX. Measurements taken from a 29-node 802.11b test-bed demonstrate the poor performance of minimum hop-count, illustrate the causes of that poor performance, and confirm that ETX improves performance. For long paths the throughput improvement is often a factor of two or more, suggesting that ETX will become more useful as networks grow larger and paths become longer. <s> BIB001 </s> A Survey on Investigating the Need for Intelligent Power-Aware Load Balanced Routing Protocols for Handling Critical Links in MANETs <s> AODV. <s> This paper describes ExOR,an integrated routing and MAC protocol that increases the throughput of large unicast transfers in multi-hop wireless networks. ExOR chooses each hop of a packet's route after the transmission for that hop, so that the choice can reflect which intermediate nodes actually received the transmission. This deferred choice gives each transmission multiple opportunities to make progress. As a result ExOR can use long radio links with high loss rates, which would be avoided by traditional routing. ExOR increases a connection's throughput while using no more network capacity than traditional routine.ExOR's design faces the following challenges. The nodes that receive each packet must agree on their identities and choose one forwarder.The agreement protocol must have low overhead, but must also be robust enough that it rarely forwards a packet zero times or more than once. Finally, ExOR must choose the forwarder with the lowest remaining cost to the ultimate destination.Measurements of an implementation on a 38-node 802.11b test-bed show that ExOR increases throughput for most node pairs when compared with traditional routing. For pairs between which traditional routing uses one or two hops, ExOR's robust acknowledgments prevent unnecessary retransmissions,increasing throughput by nearly 35%. For more distant pairs, ExOR takes advantage of the choice of forwarders to provide throughput gains of a factor of two to four. <s> BIB002 </s> A Survey on Investigating the Need for Intelligent Power-Aware Load Balanced Routing Protocols for Handling Critical Links in MANETs <s> AODV. <s> Opportunistic routing is a recent technique that achieves high throughput in the face of lossy wireless links. The current opportunistic routing protocol, ExOR, ties the MAC with routing, imposing a strict schedule on routers' access to the medium. Although the scheduler delivers opportunistic gains, it misses some of the inherent features of the 802.11 MAC. For example, it prevents spatial reuse and thus may underutilize the wireless medium. It also eliminates the layering abstraction, making the protocol less amenable to extensions to alternate traffic types such as multicast. This paper presents MORE, a MAC-independent opportunistic routing protocol. MORE randomly mixes packets before forwarding them. This randomness ensures that routers that hear the same transmission do not forward the same packets. Thus, MORE needs no special scheduler to coordinate routers and can run directly on top of 802.11. Experimental results from a 20-node wireless testbed show that MORE's median unicast throughput is 22% higher than ExOR, and the gains rise to 45% over ExOR when there is a chance of spatial reuse. For multicast, MORE's gains increase with the number of destinations, and are 35-200% greater than ExOR. <s> BIB003 </s> A Survey on Investigating the Need for Intelligent Power-Aware Load Balanced Routing Protocols for Handling Critical Links in MANETs <s> AODV. <s> We provide a comparative analysis of various routing strategies that affect the end-to-end performance in wireless mesh networks. We first improve well-known link quality metrics and routing algorithms to enhance performance in wireless mesh environments. We then investigate the route optimality, i.e., whether the best end-to-end route with respect to a given link quality metric is established, and its impact on the network performance. Network topologies, number of concurrent flows, and interference types are varied in our evaluation and we find that a non-optimal route is often established because of the routing protocol's misbehavior, inaccurate link metric design, interflow interference, and their interplay. Through extensive simulation analysis, we present insights on how to design wireless link metrics and routing algorithms to enhance the network capacity and provide reliable connectivity. <s> BIB004
AODV stands for ad hoc on-demand distance vector routing. This on-demand routing is part of dynamic source routing (DSR). However, unlike DSR, which uses source routing, AODV takes a hop-by-hop routing approach. In addition, AODV combines the concept of destination sequence numbers from destination sequenced distance vector routing (DSDV). Since AODV is reactive in nature, it builds routes only as desired by source nodes. Therefore, nodes need not maintain routes to nonactive destinations. New route requests are handled in a quicker and easier manner than those in earlier routing protocols. The route discovery of AODV is based on the exchange of RREQ (route request) and RREP (route reply) packets. For AODV with HOP, the shortest-hop path is preferred, and, hence, there is no need to process and forward later received RREQs with the same broadcast ID unless they have a higher sequence number. Duplicate RREQs that carry a better cumulative link metric value must be forwarded, so that all the possible routes are considered. AODV ensures link breakages and breakdowns are handled efficiently. AODV utilizes an RERR packet to alert the link disconnection  . When a link failure is detected and RERR is triggered, every node that receives the RERR removes the corresponding entry from its routing table and rebroadcasts it. Source nodes that use the broken link bootstrap the route establishment process by sending an RREQ. As MANET routers are not stationary, link failures due to mobility are quite common. In addition, a link is disconnected and RERR is triggered when a transmission fails due to packet collisions, interference, or inadequate link rate selection, which often occurs temporarily. Although the route rediscovery process is crucial to maintain the end-to-end connectivity, unnecessary triggering of route recovery wastes network resources. Caching the link metrics with every route requests would solve this problem to a certain extent. This demands forwarding of link metrics over route requests to every neighbor because which neighbor becomes the next hop is very much unknown. This action would end up with a situation where there are larger route request messages with increasing neighbors and eventually leads to a sizeable overhead in route setup. Much similar to the significance of time to live filed (TTL), expected transmission count (ETX) is allowed for wireless networks. DSDV (destination-sequenced distance vector) and DSR (dynamic source routing) handle ETX to find paths with maximum throughput in multihop wireless networks BIB001 . However, maximum throughput is attained only approximately due to the frequently changing topology. The spanning tree variation of AODV, called AODV-ST (spanning tree)  , combines AODV with the spanning tree algorithm. However, this is being applied in wireless mesh networks. Again, MANETs with high dynamism may find this algorithm a bit difficult due to overhead caused by fast computation. In other words, to adapt to changing topology, if MANETs should admit to increase in overhead, this algorithm may result in faster computation of routes. In addition, computing routes after addition of new nodes becomes a very common problem, and, therefore, employing AODV-ST would cost much in MANETs. A good solution to the earlier problem is to use the tree based routing not compulsory but optional BIB004 . Recently, an efficient concept for multihop routing called opportunistic routing has been introduced in the literature BIB002 BIB003 . It has been, however, implemented for mesh networks. Studies have recorded an improvement in performance gain for this new concept when operating with multicast traffic. However, its contribution to unicast traffic is not that significant.