## 2 Internet of Things (IoT): Specifications & Security Challenges
### Characteristics of IoT  
IoT has multiple features and characteristics that make it distinguished and can be summarized as follows [3; 14]:  
* Heterogeneity: IoT networks contain several types of devices that work together to form a reliable communication channel. This means different technologies, protocols, paradigms, and capabilities are used based on constraints related to the computational power of the hardware. Such technologies include wireless sensor networks (WSN), radio-frequency identification (RFID), near-field communication (NFC), and others.
* Large-Scale Architecture: A massive number of IoT network devices are connecting at a large scale level which leads to constraints on communication capabilities. Multiple challenges are introduced with regard to this matter in terms of design, storage, speed, efficiency, accessibility, and security of IoT networks. It requires standardized technologies to enhance performance and ensure proper scalability.
* Power and Cost Constraints: Due to the huge increasing number of IoT-connected devices, low-power, and low-cost solutions are used to adapt the complexity of these networks and smooth their workflow.
* Interconnectivity: Connections between IoT devices are used to conduct global and local information at various times and from any place. The type of connectivity can be determined based on the IoT-provided services. Local connections take place in services such as autonomous vehicles while the global ones can be seen in smart home services where access requires management of critical infrastructure.
* Close Proximity: IoT networks have used close proximity where dedicated short-range communication instead of using network-centric communications as in the traditional Internet. This minimizes the use of central authority through key enabling technologies of IoT such as Device-to-Device communication (D2D) and Machine-to-Machine communication (M2M).
* Reliability and Latency: IoT networks have supported the workflow of critical services using Ultra-Reliable and Low Latency communication. This can help these services such as robotic surgery, intelligent transportation system, and others by ensuring strict criteria in terms of delay and reliability of IoT network performance.  
* Autonomic Computing: IoT networks are considered an autonomic computing system that includes self-configuration, self-optimization, self-healing, and self-protection properties. Their properties contribute by allowing automatic configuration, automatic performance boosting, automatic error detection, and automatic defense mechanism, respectively. These properties support the operation of IoT systems in emergency and disaster situations [20].
* Intelligence: Smart services are incorporated with IoT networks where a decision is made in a timely manner. This can be achieved by performing analysis and processing on the massive amount of IoT-generated data followed by taking proper actions without human intervention.  
Additionally, there are multiple areas where IoT applications are adopted such as smart environment, smart agriculture, smart transport, smart health, smart energy, defense manufacturing, and industrial engineering [21].