Querying time indexed information in mobile Ad hoc networks

Time indexed information refers to information whose instance producing time is used as the search key for its access. One common scenario of querying time indexed information is to discover the information instance whose producing time is the closest to a given queried time. However, in the context of mobile ad hoc networks (MANETs), lack of infrastructure support, node mobility, and potential packet loss in wireless communications make querying time indexed information a challenging task. This paper describes a Self-Organizing Mechanism for querying Time indexed Information in MANETs, termed SOMTI. Using SOMTI, each instance producer h discovers routes to a set of instance producers whose instance producing times are the closest to a set of computed time points both before and after h's instance producing time. These routes form a web of search indices, which allow queries received by any instance producer to be forwarded in the manner of n-ary search for the instance producer whose instance producing time is the closest to the queried time. Both mathematical analysis and simulation study show that SOMTI is scalable with the number of nodes and the query producing rate. In addition, simulations results demonstrate that the goodness, in terms of the closeness to the queried time, of the discovered instance is always better than competing approaches under various node mobility speeds, query generation rates, and the number of nodes in the network, which demonstrates the effectiveness of SOMTI.