Traditionally, route discovery in MANETs operates in a source-initiated manner. This unilateral operation is unbalanced and inherently not ideal for MANETs. We propose a new scheme called bilateral route discovery (BRD), where both source and destination actively participate in a route discovery process. BRD has the potential to reduce the control overhead by one half. As an underlying protocol for BRD, we propose gratuitous route error reporting (GRER). GRER bypasses the failed link and notifies the destination of a broken route. The destination can thus play an active role in the upcoming route re-discovery. The results of an extensive simulation study confirm the effectiveness of the BRD approach.

We present a lightweight hierarchical routing model, Way Point Routing (WPR), in which a number of intermediate nodes on a route are selected as waypoints and the route is divided into segments by the waypoints. Waypoints, including the source and the destination, run a high-level intersegment routing protocol, while the nodes on each segment run a low-level intrasegment routing protocol. One distinct advantage of our model is that when a node on the route moves out or fails, instead of discarding the whole original route and discovering a new route from the source to the destination, only the two waypoint nodes of the broken segment have to find a new segment. In addition, our model is lightweight because it maintains a hierarchy only for nodes on active routes. On the other hand, existing hierarchical routing protocols such as CGSR and ZRP maintain hierarchies for the entire network. We present an instantiation of WPR, where we use DSR as the intersegment routing protocol and AODV as the intrasegment routing protocol. This instantiation is termed DSR over AODV (DOA) routing protocol. Thus, DSR and AODV—two well-known on-demand routing protocols for MANETs—are combined into one hierarchical routing protocol and become two special cases of our protocol. Furthermore, we present two novel techniques for DOA: one is an efficient loop detection method and the other is a multitarget route discovery. Simulation results show that DOA scales well for large networks with more than 1,000 nodes, incurring about 60 percent-80 percent less overhead than AODV, while other metrics are better than or comparable to AODV and DSR.

On-demand routing protocols are preferred in mobile ad hoc networks where resources such as energy and bandwidth are constrained. In these protocols, a source discovers a route to a destination typically by flooding the entire or a part of the network with a route request (RREQ) message. The destination sends a route reply (RREP) message to the source after receiving the RREQ. The RREP travels hop by hop on the discovered route in reverse direction or on another route to the source. Sometimes the RREP can not be sent to the intended next hop by an intermediate node due to the dynamic network topology or network congestion. Existing on-demand routing protocols handle the undeliverable RREP as a normal data packet - discard the packet and send a route error message to the destination (initiator of the RREP). This is highly unacceptable because a RREP message has a lot at stake - it is obtained by a large number of RREQ transmissions, which is an expensive and time-consuming process. Furthermore, the source may have to start another round of route discovery to establish the route because of the loss of the RREP. This will exacerbate the situation. In this paper, we propose the idea of salvaging route reply (SRR) to improve the performance of on-demand routing protocols. SRR attempts to salvage an undeliverable RREP in two possible ways: looking up the route cache for an alternate path and conducting a one-hop SRR route discovery. We present an implementation of SRR in AODV routing protocol. The results of an extensive simulation study confirm the performance improvement in all critical metrics, namely, packet delivery ratio, control overhead and end-to-end delay.