O3: Optimized Overlay-Based Opportunistic Routing

Opportunistic routing achieves significant performance gain under lossy wireless links. In this paper, we develop a novel approach that exploits inter-flow network coding in opportunistic routing. A unique feature of our design is that it systematically optimizes end-to-end performance (e. g., total throughput). A key challenge to achieve this goal is a strong tension between opportunistic routing and inter-flow network coding: to achieve high reliability, opportunistic routing uses intra-flow coding to spread information across multiple nodes; this reduces the information reaching an individual node, which in turn reduces inter-flow coding opportunity. To address this challenge, we decouple opportunistic routing and inter-flow network coding by proposing a novel framework where an overlay network performs overlay routing and inter-flow coding without worrying about packet losses, while an underlay network uses optimized opportunistic routing and rate limiting to provide efficient and reliable overlay links for the overlay network to take advantage of. Based on this framework, we develop the first optimization algorithm to jointly optimize opportunistic routes, rate limits, inter-flow and intra-flow coding. We then develop a practical opportunistic routing protocol (O3) based on the optimization results. Using Qualnet simulation, we study the individual and aggregate benefits of opportunistic routing, inter-flow coding, and rate limits. Our results show that (i) rate limiting significantly improves the performance of all routing protocols, (ii) opportunistic routing is beneficial under high loss rates, whereas inter-flow coding is more effective under low loss rates, and (iii) O3 significantly out-performs state-of-the-art routing protocols by simultaneously leveraging optimized opportunistic routing, inter-flow coding, and rate limits.