Hydro: A Hybrid Routing Protocol for Low-Power and Lossy Networks

Existing routing protocols for sensor networks either exclusively focus on collection-based traffic, or optimize for point-to-point traffic in a homogeneous network. As these networks become more general, a mix of these workloads in a heterogeneous setting is expected, while still abiding by the resource constraints of low-power and lossy networks (L2Ns). Our design leverages the predominantly two-tiered topology of L2N deployments, with capable border routers supplementing resource-starved in-network nodes, and optimizes for the typical traffic workloads consisting mainly of collection based traffic with specific instances of point-to-point traffic. We present Hydro, a hybrid routing protocol that combines local agility with centralized control. In-network nodes use distributed DAG formation to provide default routes to border routers, concurrently forming the foundation for triangle point-to-point routing. Border Routers build a global, but typically incomplete, view of the network using topology reports received from in-network nodes, and subsequently install optimized routes in the network for active point-to-point flows. Building on the vast existing literature on distributed DAG formation in L2Ns and centralized routing in large-scale networks, our contribution lies in the merging of these ideas in the form of a routing protocol that addresses the needs of L2Ns while remaining grounded in their inherent constraints. Evaluations across testbeds and deployments demonstrate the performance and functionality of Hydro across a variety of workloads and network conditions.