# Enhanced Three Layer Hybrid Clustering Mechanism for Energy Efficient Routing in IoT
## 1 Introduction  
Wireless Sensor Network (WSN), which is also called ear and eyes of Internet of Things (IoT), becomes an important research topic due its increasing role and usage in many applications. WSN as a connecting bridge between real and digital worlds is a fast growing field of IoT that provides the required data from the field accurately with low cost. The common vision of different IoT wireless systems is usually associated with same concept, use of networked embedded devices to achieve intelligent monitoring and management. Devices are interconnected to transmit useful measurement information and control instructions via distributed sensor networks. WSN is widely used in both delay tolerant and real time applications. Some well known usages of WSNs are: Smart cities and smart homes applications, environment and wildlife monitoring, security and military related applications, disaster management and rescue applications, and others [1]. The application area of WSN is enlarging day by day, with rapid development in the fields of low power consuming wireless communication [2] and digital electronics [1]. WSN consists of one or more sink nodes, and many sensor nodes. Usually a large number of homogeneous nodes are deployed randomly in the field of interest to collect required attributes and transmit them towards the sink node, which in turn forwards these data packets to the nearest station. A sensor node is typically a tiny electronic device equipped with: Low cost micro controller with very low power consumption, one or more sensors that gather data of interest from the surroundings, limited battery which is assumed to neither be replaced nor recharged as the power source, flash memory, and transceiver that uses Radio Frequency (RF) for communication with other nodes. Laser and infrared are also can be used for communication instead of RF in some WSN applications, but they are sensitive to atmospheric conditions, and also require line of sight. RF based communication is most popular in WSN applications. License free Industrial Scientific and Medical (ISM) frequencies radio bands such as 433 MHz, 915 MHz, and 2.4 GHz are mostly used in WSNs. It is obvious that these small low cost sensor nodes are neither accurate nor powerful as compared to the expansive macro sensor nodes, but a good quality sensor network still can be made by using large number of these nodes together. Normally, these nodes are deployed randomly in remote areas where deployment of large expansive nodes is not possible due to high cost or harsh environment. Sensor nodes have limited source of power and their batteries in most cases cannot be recharged or replaced due to many reasons such as: Large number of deployed sensor nodes, random deployment of sensor nodes, remote location of the sensing region, and harsh environment. Therefore, energy remains the main issue and there is always a need for algorithms and mechanisms that reduce network energy consumption and balance consumption of power between all deployed sensor nodes, in order to prolong the network life time. Unlike sensor nodes, the sink node is assumed to have no power constraints and its main task is to gather sensed information from the deployed sensor nodes and forward them to the nearest station. A sensor node mainly use energy in two conditions. The first condition is when a sensor node performs tasks such as transmitting data packets, receiving data packets, processing requests; which are called useful tasks. While operations such as transmission and reception of control packets with neighboring nodes for upper or lower layer head selection or for choosing better forwarder, retransmissions, overhearing, processing redundant packets, and similar other operations come under second condition, which is considered a waste of energy. Network lifetime is considered a major factor in performance evaluation of routing protocols for WSN when sensor nodes have limited power source.