## 1 Introduction  
The Industrial Internet of Things (IIoT) is a recent and growing research area concerning the application of the Internet of Things (IoT) and related technologies such as Wireless Sensor Networks (WSN) in order to improve the productivity/performance of several industrial processes and systems [1]. The IIoT leverages the IoT paradigm to improve connectivity, efficiency, scalability and cost savings of different manufacturing industries and organizations. The IIoT has been recently applied in several important domains including in smart industry applications [2; 3; 4], smart manufacturing [5] and smart city applications [6; 7; 8]. Despite being contemporary, the success of the IIoT strongly depends on the advances being made in the study of WSNs [9]. This dependence exists because most IIoT deployments are mostly based on the use of sensors, which are components of the WSNs. In this regard, several existing research challenges regarding WSNs are actively under consideration in the literature. One problem is the growing heterogeneity being created by the increased development and deployment of different sensor nodes in WSNs, which prevent the co-existence of different WSN nodes on a shared physical infrastructure. This heterogeneity introduces difficulties including the interoperability problem across different administrative domains, slow deployment rates of WSNs, conflicting goals and economic interests of different WSNs node vendors, and the increasing cost of WSN deployments. In order to address these challenges, the concept of virtualization in sensor networks has been introduced. Sensor network virtualization is aimed at providing flexibility in the deployment of WSNs, providing cost-effective solutions, improving seamless interoperability and enhancing security and management facilities. In technical terms, a virtualized wireless sensor network (VWSN) is formed by delivering logical connectivity to a subset of collaborating nodes in order to accomplish a specific task or application at a given time. These nodes are grouped based on the physical condition that these nodes may be tracking or monitoring per time. Based on the success of VWSNs, the recent concept of overlay VWSN (OVWSN) has consequently gained similar popularity, particularly for enhancing the performance of WSNs. The concept of OVWSN, especially within the existing WSN infrastructure, will increase the reuse of different sensor infrastructures. This is possible because virtualization decouples the network infrastructure from the application services and replaces current direct connections with virtual/logical links. These logical links require the application services to choose the optimal node(s) to use in a particular situation, as opposed to the fixed allocation of nodes to a specific application task(s). The physical resources are thus allocated on-the-fly and on-demand using possible dynamic resource allocation techniques. This concept ensures that resources are efficiently utilized and shared between different application tasks. Current and future deployment of sensor networks will require efficient and powerful devices to be used as sensor nodes. Thus, feature-rich and resource-abundant devices should be available to create a platform for VWSN, such that sensor nodes can share resources among a variety of applications to avoid unnecessary and redundant deployment of nodes. Virtualization allows users (applications and services) to use resources dedicated to them [10; 11]. By complementing the concept of virtualization, overlaying further allows the creation of new services at the edge of the existing infrastructure with little or no change to the underlying hardware. A combination of virtualization and overlay services will enable robust, scalable and resilient WSNs. Besides, virtualization addresses the gap of domain-specificity in wireless sensor deployment.