## 1 Introduction  
Advances in electronic industry and producing sensors with high sensing and processing abilities could bring promising applications to various aspects of today's life; mainly, high-tech industries, healthcare systems, military, agriculture, and so on [1, 2]. Sensor-nodes are able to communicate with each other or with other devices to share their sensing information. Therefore, diverse types of network topologies can be constructed in the category of Wireless Sensor Networks (WSNs) [3]. Due to very vast developments in the Internet technology around the world, people become more interested to bring the Internet to all of the aspects of life. Indeed, there is no limitation for the applications that the Internet can involve for changing the style of humans' life. This very big goal could become achievable by the idea of IoT (Internet of Things) which was proposed in 1999 by [PERSON] [4, 5]. As shown in Figure 1, WSNs play a major role in IoT since sensor-nodes can provide the opportunity to observe and monitor any environment. Due to limited capabilities of the sensor-nodes and complexity of the environments; in most of the applications, a standalone sensor-node cannot connect to the Internetdirectly. Therefore, a WSN can work as a bridge between the sensor-nodes and the Internet. Clearly, any improvement in WSNs can extend the usability of IoT especially new improvements in large-scale WSNs which is our main concern in the current work [6]. In large scale WSNs, hundreds or even thousands of sensor-nodes are being distributed in harsh and unattended environments to capture natural phenomena and their changes. Due to the use of mostly non-rechargeable batteries in the sensor-nodes, balancing energy consumption is the main design issue that can guarantee the lifetime and reliability of the network. One of the common problems that is related to nonuniform energy depletion is hot-spot phenomenon in that the sensor-nodes which are closer to the base-station will die earlier in contrast to the sensor-nodes which are located far from the base-station by maintaining more than 90% of their initial energy [7]. Recently, employing mobile-sink(s) in the network becomes one of the efficient solutions to balance energy-consumption among the sensor-nodes [8; 9; 10; 11; 12; 13]. The main idea behind this solution is that the mobile-sink(s) can move across the network and harvest the data from the sensor-nodes and reduce or eliminate the number of hops in the fashion of multi-hop communication. Beside the simplicity of this idea, due to the limitations of mobile-sink as a vehicle that should move in a physical environment and the scale of WSNs, there are two main challenges which are in the state of research. The first challenge is about the fashion of movement for the mobile-sink(s) in the network. And the second one addresses the visiting strategy of the mobile-sink(s) that should visit all of the sensor-nodes one-by-one or adopting a visiting approach for a set of sensor-nodes which work as Rendezvous Points (RPs) in the network. Indeed, the application scenario is the most important factor that can lead to different considerations. Due to enough processing capabilities in most of the sensor-nodes recently, Event-Driven Wireless Sensor Networks (EWSNs) are introduced in [14; 15]. Compare to typical WSNs that each sensor-node is responsible for capturing measurement values and sending them to higher layers for further processing; In EWSNs, all of the sensor-nodes are able to process the measurement values individually, and then by recognizing an event, report the event-alarm to higher layers. Based on the nature of events in the environment, the sensor-nodes should be equipped with different algorithms for event detection. For example, some events can be defined based observing a value more than a predefined threshold such as (temperature \(\geq\) 70 \({}^{\circ}\)C). Therefore, a sensor-node triggers an event alarm by capturing a value more than the threshold.