Technical Report MSC-2011-15

Title: A Density-Driven Publish Subscribe Service for Mobile Ad-Hoc Networks
Authors: Anna Kaplun
Supervisors: Roy Friedman
Abstract: We study a density driven virtual topography based publish/subscribe service for mobile ad-hoc networks. Mobile Ad-Hoc Networks (MANETs) are formed by a collection of mobile nodes, each equipped with wireless communication capabilities, without relying on any fixed infrastructure or centralized administration. In order to maintain network connectivity, each node may act as an ad-hoc router, forwarding data packets for other mobile nodes that may not be within direct transmission range of each other. We explore three variants of a publish/subscribe service that is based on the virtual topography. In the first, nicknamed 3DLS-Pub/Sub, nodes send their publications to the several hilltops using a local greedy walk. Based on the properties of the virtual topography, this walk usually follows a very short path. Then, periodically, each node sends a lookup message, which carries its subscriptions and traverses several hilltops. In each encountered hilltop, the lookup message checks whether the visited hilltop stores matching events. This way, it collects all matching events, and returns them to the initiator. The second approach, nicknamed LCDD-Pub/Sub, improves on 3DLS-Pub/Sub message count and message sizes by employing a network estimation mechanism. The last scheme, called LDDD-Pub/Sub, utilizes the opposite approach. That is, subscriptions are forwarded to the nearest hilltop. Events are published to multiple hilltops. Each hilltop through which the publication passes, checks which nodes have matching subscriptions, and forwards the event to them using optimized routing. This results in much faster event notification, at the expense of a higher message count. We perform an extensive simulation based study, in order to explore the operational envelop and performance of our proposed schemes. We also compare them with the tree-based publish/subscribe mechanism and an optimized flooding based scheme. Our results show that the density driven approach is superior to the others in most scenarios for most metrics. The only exception is for applications that require extremely fast notifications (sub-second). For the latter, flooding based is the most adequate, yet this comes with a price of transmitting much more messages than the tree-based and density-based approaches.
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