Page 2 Lecture Notes in Computer Science 2865 Edited by G. Goos ...

5 Related WorkDelivering Messages in Disconnected Mobile Ad Hoc Networks 81The problem of message delivery among disconnected Mobile Ad-Hoc Networksis not new to the research community. In particular, the idea of using intermediatenodes to relay messages among disconnected hosts has also been proposedearlier by Li and Rus [7]. Different research groups have approached the problemof delivery in a disconnected network from the perspective of different MANETapplications and hence have come up with different solutions. Karumanchi et.al. [8] describe the problem of network partitioning in a MANET formed bya group of firefighters involved in a firefighting mission. Each firefighter is requiredto update its location information to servers in the network and must beable to obtain location information of other firefighters by querying the servers.Their solution employs quorum-based strategies to update and query informationin a partitioned network. Wang and Li [9] describe the problem of networkpartitioning among group of mobile nodes that are requesting and downloadinginformation on demand from a centralized service. Their goal is to provideservice coverage even when the network is partitioned by replicating the serviceto appropriate nodes before a partition takes place. They employ a partitionprediction scheme to predict partitioning in the network before it occurs [12].Li and Rus [7] consider the problem of network partitioning in a domain whereit is possible to instruct mobile nodes to change their trajectories, such as in arobotic network where a team of robots is deployed to perform sensing tasks ina remote or hazardous environment.6 Future WorkWe have not reseached the parameter space completely, we plan to run moresimulations and determine the sensitivity of our protocol to more parameters. Weare also considering several extensions and improvements to our basic scheme.These are described in the next subsections.6.1 Reducing OverheadThe network overhead seems to override the benefit of replication in our protocolwhen the number of nodes is large. We are working on several approaches tosolve this problem. One of them is to use a cache to buffer the neighbour listsof neighbouring nodes as it seems wasteful to ask for neighbour lists for eachmessage. A cache entry containing the neighbour list of a mobile node would bevalid for a short period of time and all neighbour list requests sent to the mobilenode within that period will be serviced from the cache. This can help reduceneighbour list request and reply traffic in the network. But this would raise otherissues; specifically, the status information provided by a neighbour in a NBREPmessage would be lost. It is to be evaluated how much of a trade-off this is betweenreducing overhead and accuracy. Another approach to reduce neighbourlist request traffic is to broadcast the NBREQ message. One approach to reduce