The IoT architecture is distinguished in six layers as indicated below :
- • Coding Layer; It is related to the basic layer of the IoT architecture where the object of interest is provided with a code for the sake of unique identification.
- • Perception Layer: This layer is also known as device layer or recognition layer. The devices are usually RFID sensors, IR sensors, and sensors that are responsible for the temperature, pressure, moisture, speed, location, etc. The data sensor gathers the information, converts it to digital signal, and transmits it to Network layer.
- • Network Layer; It is responsible for secure data transmission between Perception and Middleware layer. This layer receives the information from the
Perception layer in digital form and then sends it to the Middleware layer for further processing.
- • Middleware Layer: This layer uses ubiquitous computing, cloud computing, fog computing, edge computing, etc., to access the database directly and store the required information in it.
- • Application Layer: This layer provides the personalized service on the basis of user needs, using the result of the processed data.
- • Business Layer: The Business layer is the higher level of the IoT architecture, where various business models are generated for the effective business strategies (Figure 6.3).
IoT Technologies for Smart Cities
The development of IoT network utilizes various communication protocols and consists of several objects that can be measured, inferred, understood, and can change the entire environmental conditions. Based on that, the IoT ecosystem consists of smart devices and other relevant technologies that can be described as follow:
- • Radio-Frequency Identification (RFID): The RFID systems consist of readers and tags which are playing a key role in the IoT. This technology can be applied to any IoT object carrying out the automatic identification and assign a unique digital identity to each object. The reason behind that is to be incorporated in the network and related to the digital information and service 
- • Wireless sensor network (WSN): The advantage of a WSN is that it can be used in many cases such as healthcare, government, and environmental sendees. Furthermore, the WSN can be integrated with RFID system to obtain information regarding the position, movement, temperature, etc .
- • Addressing: The interconnection between people and objects, in order to establish smart environments is crucial for favorable outcomes of the IoT. This is because uniquely addressing the large-scale combination of objects is vital for controlling them via the Internet 
FIGURE 6.3 IoT Architecture Layers
- • Middleware: The middleware plays a key role in the interconnection of the objects to the application layer. The key objective of the middleware is to concisely integrate the functionalities and communication capabilities of all involved devices .
- • Cloud Computing: The cloud computing technology is one of the core parts of the IoT as it stores, processes and presents the analysis of all aggregated data from various IoT devices. It can converge many servers on to one cloud platform with an objective to share the resources and access them from anywhere and anytime. As the IoT devices increase rapidly and fully depend on the cloud, there is a need for more development of this technology to unleash its true power .
- • Data Storage and Analytics: The critical factors that affect the growth of data are its storage, data ownership, and data expiry. Algorithms that make use of intelligent data and are either evolutionary, centralized, or distributed should be designed for effective decision making. The systems thus created must possess characteristics such as interoperability, integration, and adaptive communications. The system is based on modular architecture for hardware and software development .
- • Visualization: Visualization allows the user interaction with the virtual environment. The visualization of the IoT application can be easily achieved through the advances in the touch screen and speech recognition technologies. The conversion of data into information to knowledge will lead to faster decision-making process .
IoT Applications for Smart Cities
The IoT utilizes the Internet to incorporate heterogeneous devices with each other. In this regard and in order to facilitate the accessibility, all available devices should be connected to the Internet. In order to achieve this target, sensors can be developed at different locations for collecting and analyzing data to improve the usage.
Smart Homes: As indicated in the ENISA’s report , smart home environments have the ability to integrate multiple IoT devices and services that collect, process, and exchange data. They provide users with the possibility to control and adapt the status of their home, either manually or automatically. There exist interactions that take place between the internal and external actors of smart home devices and services. Smart Home Environments being an emerging domain and because the liabilities are not well defined, it becomes important for all actors to develop adapted security measures to prevent cyber-threats. For that purpose, there is a need to secure Smart Home Environments and effectively reduce the threats.
Smart Healthcare: Smart healthcare is an intelligent infrastructure that uses intelligent infrastructure that uses sensors to perceive information, transmits information through the IoT, and processes the information using supercomputers and cloud computing. Smart healthcare is defined as a health service system that uses technology such as wearable devices, IoT. and mobile internet to dynamically access information, connect people, materials, and institutions related to healthcare. Smart healthcare can also promote interaction between all parties in the healthcare field, ensure that participants get the services they need, help the parties make informed decisions, and facilitate the rational allocation of resources. In a nutshell, smart healthcare is a higher stage of information construction in the medical field . The various components of smart healthcare include emerging on body sensors, smart hospitals, and smart emergency response. In smart hospitals, various mechanisms are used, including ICTs, cloud computing, smartphone apps, and advanced data analysis techniques [I].
Smart City and IoT: Challenges and Opportunities
Smart cities challenges are categorized into city traffic, citizen behavior, and city planning. Sensors for GPS, GIS attached with vehicles can analyze the traffic in real time. Big data research challenges of smart cities are categorized into two. Business challenges (Planning, Sustainability, Cost, Integration with Cloud computing) and Technological challenges (Privacy, Data analytics, Data formats, and QoS). Smart city challenges originate from its design to operation such as design & implementation cost, technology identification, heterogeneity of devices, volume of data, Cybersecurity issues, dynamic future adoption, and connectivity speed. With the available network technologies and mechanisms, smart city is getting matured and more realistic .
- • Design and Implementation Cost: Smart IoT requires procurement and installation of new devices and software for stepping into cloud & big data paradigm. Most of the existing city administrative procedures have to be changed accordingly. Placing the sensors in the appropriate locations without affecting the people’s convenience and privacy is still a concern .
- • Heterogeneity: The devices, technologies, software, and platform are different for each IoT system. All these data should be integrated and processed in the cloud. Interoperability issues impact the IoT integration and device communication. Though standards are existing, it is not evolved completely to manage the different IoT platforms .
- • Volume of data & devices: Considering multiple thousands of sensors installed in the city and monitored almost of the day in real time, volume is so huge to handle. Data generation, communication and processing require separate tools and strategy for each IoT system. Sensor and IoT devices deployment at large scale in a city poses significant challenges in managing, processing, and interpreting the big data they generate .
- • Cybersecurity: Prevention of intrusion is important in cyber-physical systems. As the internet is the backbone of IoT. cyber-attacks are very common and hackers try to steal the citizen data. Hence, it is necessary to design and implement IoT system against these types of attacks .
- • Dynamic adoption: IoT technologies are getting matured every day and adapting to the newer with the existing IoT system is quite challenging with minimal changes. IoT sustainability is required for the long run of smart cities by identifying the system which accepts the new technical viability .
- • Connectivity speed: Most of the IoT systems generates real-time data and should be processed and available immediately. Hence, high-speed networks such as 4G/5G is essential in the IoT communication gateway .
• Security Issues: Smart IoT should be secure since it involves lot of citizens network is the major challenge in the smart cities project. Though there were many technological solutions available, intrusion may happen, which is inevitable. Both proactive and reactive measurements have to be placed in the IoT design .