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Sensor networks are increasingly being deployed for fine-grain monitoring of physical environments subjected to critical conditions such as fire, leaking of toxic gases and explosions. A great challenge to these networks is to provide a fast, reliable and fault tolerant channel for events diffusion, which meets the requirements of query-based, event-driven and periodic sensor networks application scenarios, even in the presence of emergency conditions that can lead to node failures and path disruption to the sink that receives those events. This paper presents a fault tolerant and low latency algorithm, which we refer to as PEQ (Periodic, Event-Driven and Query-Based Protocol), that meets sensor networks requirements for critical conditions surveillance applications. The algorithm uses the publish/subscribe paradigm to disseminate requests across the network and an ack-based scheme to provide fault tolerance. The algorithm was implemented using NS-2 simulator and compared to the Directed Diffusion paradigm. Important metrics were evaluated showing that the proposed algorithm can be a proper solution to meet constraints and requirements of events delivery in critical conditions monitoring applications.

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Applications that require fine-grain monitoring of physical environments subjected to critical conditions, such as fire, leaking of toxic gases and explosions, pose a great challenge to sensor network protocols. These networks have to provide a fast, reliable, fault tolerant and energy aware channel for events diffusion, which meets the requirements of query-based, event-driven and periodic sensor networks application scenarios. These requirements have to be met even in the presence of emergency conditions that can lead to node failures and path disruption to the sink. This paper presents HPEQ (Hierarchical Periodic, Event-driven and Query-based), a cluster-based routing protocol that groups sensor nodes to efficiently relay the sensed data to the sink. In HPEQ protocol nodes with more residual energy are selected as aggregator nodes that relay data to the sink by uniformly distributing energy dissipation among the nodes, and reducing latency and network data traffic. HPEQ is based on a previous protocol, PEQ, that meets sensor networks requirements for critical conditions surveillance applications. HPEQ uses the publish/subscribe paradigm to disseminate requests across the network. The algorithm was implemented using NS-2 simulator and compared to PEQ and to the Directed Diffusion paradigm. Important metrics were evaluated showing that the proposed algorithm can be a potential solution to meet constraints and requirements of events delivery in critical conditions monitoring applications.