GeoQuorums: Implementing Atomic Memory in Mobile Ad Hoc Networks

Abstract

We present a new approach, the GeoQuorums approach, for implementing atomic read/write shared memoryin mobile ad hoc networks. Our approach is based on associating abstract atomic objects with certain geographiclocations. We assume the existence of focal points, geographic areas that are normally “populated” by mobile nodes.For example, a focal point may be a road junction, a scenic observation point, or a water resource in the desert. Mobilenodes that happen to populate a focal point participate in implementing a shared atomic object, using a replicated statemachine approach. These objects, which we call focal point objects, are then used to implement atomic read/writeoperations on a virtual shared object, using our new GeoQuorums algorithm. The GeoQuorums algorithm uses aquorum-based strategy in which each each quorum consists of a set of focal point objects. The quorums are used tomaintain the consistency of the shared memory and to tolerate limited failures of the focal point objects, caused bydepopulation of the corresponding geographic areas. We present a mechanism for changing the set of quorums onthe fly, thus improving efficiency. Overall, the new GeoQuorums algorithm efficiently implements read and writeoperations in a highly dynamic, mobile network.