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

Delivering Messagesin Disconnected Mobile Ad Hoc NetworksRitesh Shah and Norman C. HutchinsonDepartment of Computer Science, University of British Columbia{rshah,norm}@cs.ubc.caAbstract. Many routing protocols for mobile ad hoc networks havebeen developed. These protocols find a route to a destination if such aroute exists. We present a novel protocol that delivers messages betweendisconnected hosts, that is, when no route exists between them. Ourprotocol uses the nodes moving between the neighbourhoods of the sourceand destination nodes to act as carriers of the messages. We describe theprotocol in detail, provide an initial simulation-based evaluation of itsperformance compared to both a naive scheme and the optimal scheme,and discuss some extensions to the protocol that we are exploring.1 IntroductionAn ad-hoc network is a self-starting network formed on-the-fly by a group ofmobile nodes without the aid of any centralized administration or establishedinfrastructure. Ad-Hoc networks find their use in situations where no fixed wiredinfrastructure is available or has been damaged by natural or man-made disaster.Rapid advancement in wireless technology and increasingly affordable pricesof wireless devices have made ad-hoc networks a reality. This has fuelled a lot ofresearch activity in the field. Several protocols [1], [5], [6] have been developed tofind and maintain routes between the nodes of an ad-hoc network. These routingprotocols can be divided into three broad categories. First are the pro-activeprotocols, that use periodic advertisements to broadcast routing information,such as DSDV [2]. Second are on-demand protocols, that search for routes ondemand,such as AODV [4] and DSR [3]. Third are those routing protocols thatuse a hybrid approach, which is a combination of the first two approaches. Whileeach approach has its advantages and disadvantages in finding a route betweentwo mobile hosts when one exists, none of them handle the case of messagedelivery between two disconnected hosts.Links in a MANET (Mobile Ad-Hoc Network) are susceptible to frequentbreakage due to movement of nodes. This may cause some nodes to get disconnectedfrom others. A message destined to such a disconnected node results ina delivery failure irrespective of the routing protocol used. Different protocolshandle this situation differently but at most they invalidate the route, if therewas one already in use and inform the source about the situation.Why is the question of message delivery among disconnected hosts important?Consider a disaster relief scenario. Relief workers are working on severalS. Pierre, M. Barbeau, and E. Kranakis (Eds.): ADHOC-NOW 2003, LNCS 2865, pp. 72–83, 2003.c○ Springer-Verlag Berlin Heidelberg 2003