I. Introduction
Wireless sensor networks (WSNs) have been receiving a considerable attention as an alternative solution for scalable monitoring and data collection in a hostile or unattended area. A WSN consists of resource-constrained sensor nodes (later nodes) in terms of sensing, computing, or communicating capability. As a part of rapidly emerging Internet of Things (IoT), where a myriad of multiscale nodes and devices are seamlessly blended, WSNs will play an important role in building a ubiquitous computing and communication infrastructure. With the prevalence of cloud, social media, and wearable computing as well as the reduced cost of processing power, storage, and bandwidth, it is envisaged that wirelessly connected smart nodes and devices under IoT will enhance flexible information accessibility and availability as well as change our life further.