Salvaging Route Reply for On-Demand Routing Protocols in Mobile Ad-Hoc Networks

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