# A Review on Internet of Things for Defense and Public Safety
## 5 Building IoT for Tactical and Emergency Environments  
In order to understand the complex adoption of IoT for defense, this section will briefly review the basics of IoT landscape (a graphical overview of the main elements can be seen in Figure 10) to support the requirements previously explained. First, it focuses on the architecture with an overview of the most important elements. Next, the section examines the main standardized protocols and technologies. The increasing number of IoT proposed architectures has not converged to a reference model [113] or a common architecture [114]. In the latest literature, it can be distinguished among several models, as it can be seen in Figure 11. For example, the basic model which has three layers (application, network and perception layers) was designed to address specific types of communication channels and does not cover all the underlying technologies that transfer data to an IoT platform. Other proposals include a middleware based layer [115], a Service-Oriented Architecture (SOA) based model [116], and a six-layer model. There are differences between these models: for example, although the architecture is simpler in the three-layer model, layers are supposed to run on  
Figure 11: The IoT architecture. (**a**) Three-layer; (**b**) Middleware-based; (**c**) Service-Oriented Architecture (SOA)-based; (**d**) Six-layer. Figure 10: IoT landscape. resource-constrained devices, while a layer like \"Service Composition\" in the SOA-based architecture takes a rather big fraction of the time and energy of the device. Next, we provide a brief description on the functionality of the most common layers. * Perception layer: this first layer represents the physical elements aimed at collecting and processing information. Most COTS IoT devices are designed for benign environments and currently focus on home automation, personal services and multimedia content delivery. Miniaturized devices such as transducers (sensors and actuators), smartphones, System on Chips (SoCs) and embedded computers are getting more powerful and energy efficient. The next generation of processors includes new hardware features aimed at providing highly trusted computing platforms. For example, Intel includes an implementation of the Trusted Platform Module (TPM) designed to secure hardware through cryptography. Technologies such as ARM TrustZone, Freescale Trust Architecture, and Intel Trusted Execution enable the integration of both software and hardware security features [32]. Plug-and-play mechanisms are needed by this layer to configure heterogeneous networks. Big data processes are initiated at this perception layer. This layer transfers data to the Object Abstraction layer through secure channels. * Object Abstraction Layer: it transfers data to the Service Management layer through secure channels. To transfer the data, the protocols used in the COTS IoT nodes either use existing wireless standards, or an adaptation of previous wireless protocols in the target sector. Typically, IoT devices should operate using low power under lossy and noisy conditions. Other functions like cloud computing and data management processes are handled at this layer [117]. * Service Management Layer or Middleware: this layer enables the abstraction of specific hardware platforms. It processes the data received, takes decisions and delivers the services over network protocols [118]. * Application Layer: it provides the services requested to meet users' demands. * Business Management Layer: this layer designs, analyzes, develops and evaluates elements related to IoT systems, supporting decision-making processes based on Big Data. The control mechanisms for accessing data in the Applications layer are also handled by this layer. It builds a business model based on the data received from the Application layer. Moreover, this layer monitors and manages the underlying four layers, comparing the output of each one with the output expected to enhance services and maintain users' privacy [119].