###### Abstract  
Wireless sensor networks (WSNs) and the Internet of Things (IoT) are increasingly making an impact in a wide range of domain-specific applications. In IoT-integrated WSNs, nodes generally function with limited battery units and, hence, energy efficiency is considered as the main design challenge. For homogeneous WSNs, several routing techniques based on clusters are available, but only a few of them are focused on energy-efficient heterogeneous WSNs (HWSNs). However, security provisioning in end-to-end communication is the main design challenge in HWSNs. This research work presents an energy optimizing secure routing scheme for IoT application in heterogeneous WSNs. In our proposed scheme, secure routing is established for confidential data of the IoT through sensor nodes with heterogeneous energy using the multipath link routing protocol (MLRP). After establishing the secure routing, the energy and network lifetime is improved using the hybrid-based TEEN (H-TEEN) protocol, which also has load balancing capacity. Furthermore, the data storage capacity is improved using the ubiquitous data storage protocol (U-DSP). This routing protocol has been implemented and compared with two other existing routing protocols, and it shows an improvement in performance parameters such as throughput, energy efficiency, end-to-end delay, network lifetime and data storage capacity. WSNs; IoT; heterogeneous WSN; multipath link routing protocol (MLRP); hybrid-based TEEN; ubiquitous data storage protocol (U-DSP) +
Footnote †: journal: _articles  
0000-0001-999-22000/0000-00001-9999-22000/00001-99999-22000/00001-99999-22000/00001-99999-22000/00001-99999-22000/0001-999999-22000/0001-999999-22000/0001-999999-22  
information is gathered and transmitted to the base station (BS). The sensor and data communication units of SNs consume more energy and once the entire energy is exhausted, it expires or is unable to process [1]. Hence, a node that is considered dead is unsuitable for either replacing with or recharging using an alternate power source. Hence, balancing the power utilization of a SN is more essential. To overcome these challenges, several developers have used clustering approaches [2], which can scale up the network lifetime and provide remarkable efficiency. Furthermore, it is supportive in maintaining power as numerous reliable clusters are formed. These clusters, based on the techniques used, can either be considered temporary or permanent. Moreover, clustering distributes the nodes that are placed jointly, which is accomplished based on similarity metrics such as the distance from the base station (BS), radius of transmission and density of the cluster. After the clusters are formed, a node from the cluster is chosen as the cluster head (CH) whose responsibility is to organize the data gathered from cluster members (CM) and transmit those data to the BS. When a single node cluster is considered, it mandatorily communicates with the sink rather than the BS, which finally results in a reduction in power utilization. In WSNs, the serious threats, along with the technical challenges, which arise due to the nature of resource constraints and its limited availability [3], have to be focused on to ensure revision and distribution. With WSNs in an open area, the sensors are more vulnerable to the unfriendly environment that arises due to humidity, increased temperature, pressure, snow, rain, dust and so on. These affect the functions of the wireless sensor network, and hence a demand arises to introduce robust and flexible SNs. Moreover, general and future challenges are constrained to the limited resources, the limited ability of communication, fault tolerance, stability, mobility, bandwidth, precision, reliability, availability, heterogeneity, accountability, uncontrollable setup and denial of service (DoS). Above all, some specific challenges have turned the attention of the researchers towards the utilization of power, network duration, throughput, security and routing protocols.