a paradigm shift in the Internet technology that is rapidly developing by the advancements in other enabling technologies such as sensor networks, mobile devices, wireless communications, networking, and cloud technologies that results into Industrial IoT (IIoT), an application of IoT in industries. So, now, we will discuss those associated technologies which bring such technological revolution in association with IoT.
1.3 IoT-Associated Technology
In Inter-networked of Things, stake holding technologies expect trillions of Sensors, billions of Smart Systems, and millions of applications in near future. There are numerous supportive technologies with IoT to perform smarter than before. IoT Associative Technology can be classified into four sub-topics, namely,
(i) Sensor and Actuators,
(ii) IoT Networking,
(iii) IoT Connectivity Technologies, and
(iv) IoT Communication Protocol.
(i) Sensor and Actuators: Sensor and Actuators are the most essential and core components of the IoT. As per oxford dictionary, the meaning of sensor is “It is a device which detects or measures a physical property and records, indicates or otherwise responds to it.” [31]. So, sensors basically sense the physical observable fact around us from an environment. As per the other sources [32], sensors can be defined as “A sensor detects (senses) changes in the ambient conditions or in the state of another device or a system, and forwards or passes this information in a certain manner”. According to this definition, a sensor can sense or detect the physical phenomena or measured properties such as temperature, humidity, smoke detection, and obstacle detection. So, we have different specific sensors that can be used to sense particular properties and cannot be used to sense or to detect, or be insensitive to the other properties surrounding us, i.e., specific physical properties can only be detected by specific sensors not bothering about other properties surrounding us. For example, a temperature sensor can sense heat (temperature) around us and then these sensed values are converted into its equivalent electrical signals.The smallest change that can be detected and can be measured by a sensor as an output is known as resolution. Based on the output, the sensor can be classified into two categories: Digital Sensor and Analog Sensor. Analog Sensor can generate or produce a continuous output signal equivalent to continuous measured property in nature; e.g., temperature, humidity, pressure, and speed are analog quantities. While Digital Sensor produces binary output (0 or 1, ON or OFF) signal. So, it generates a non-continuous (discrete) value in the form of bits that combine to gather generated byte as an output. Based on the output data types, sensors can be classified into two major groups: Scalar Sensor and Vector Sensor. Scalar Sensor generates output proportional to quantity measured from surroundings without considering its orientation or direction, e.g., physical quantity such as temperature and pressure. Vector Sensor generates the output that is proportional to quantity measured as well as its orientation or direction, e.g., physical quantities such as sound and velocity.Based on sensed information from sensors, actuators basically perform some actions (actuates) on the physical environment. So, here, actuators take actions based on what has been sensed and in that way controls a system that can be acted upon an environment. In this context, the actuators require some control signal and source of energy to function further. So, when actuators receive such control signals, they convert the energy into mechanical motion. Based on their functional domains, we have three broad categories of actuators such as pressure-based actuators (hydraulic and pneumatic), electric-based actuators (electrical, thermal, and magnetic), and mechanical-based actuators. Other than these types of actuators, other popular actuators are used in industries. Agriculture uses Soft actuators. Soft actuators are polymer-based actuators designed to handle delicate objects and used in robotics.“Transducer” is another associative term which can be used for both Sensors and Actuators [33]. So, actuators sense the surroundings in the form of information and are converted into electrical signals; such control signals are received by actuators and action is taken accordingly. For example, in “soil moisture and water level monitoring application”, agriculture soil water/moisture level in a farm is sensed by specific sensors, is converted into electrical signal, and is provided to the actuator as “solenoid valve”. Solenoid valves consist of a mechanism that allows or stops the water flow. So, depending on the electrical signal received from the sensor (water/moisture level), this solenoid valve as an actuator can actuate, i.e., flow water or stop water.
(ii) IoT Networking: IoT Network consists of several components such as Device (The Thing), Local Network, Internet, Backend services, and Applications. Here, in case of “Device”, it consists of a collection of sensors and actuators that can act as one component in the entire IoT Network. These become different nodes in the IoT Network that can be communicated with each other. As shown in Figure 1.3, a node in IoT Network can be communicated with other target node via another component of IoT network, i.e., Local Network. If target node does not belong to the local network, IoT network will search it through another component of IoT network, i.e., Internet. In Backend services, the data may be received from local networks or from the internet and perform complex analysis using different machine learning algorithms.Such result generated after complex analysis is given to applications that serve as an output of IoT Network. Thus, IoT is a very complex system that involves things (sensors and actuators), local area network, wide area network (internet), machine learning, and analysis algorithms which act mutually into one system entity.Such result generated after complex analysis is given to applications that serve as an output of IoT Network. Thus, IoT is a very complex system that involves things (sensors and actuators), local area network, wide area network (internet), machine learning, and algorithms which act mutually into one system entity.So, to perform function through IoT we need more associative technology such as Bigdata, M2M communication, cloud computing, Cyber Physical System (CPS), 3G/4G/5G, and Internet of Vehicles (IoV). To perform suitable communication among such heterogeneous technologies and devices, we need to deal with certain challenges of IoT. They are securities, interoperability, scalability, energy efficiency, and interfacing. IoT connectivity technologies are involved in IoT communication to execute it properly. They are as per the sub topics given below.
(iii) IoT Connectivity Technology: Connectivity among devices is fundamental when we think about the IoT. There are several IoT connectivity technologies in the form of communication protocols that utilize IoT networks to perform communication between IoT devices (Things). IoT service offering protocols such as RFID (Radio Frequency Identification), CoAP (Constrained Application protocol), XMPP (Extensible MessagingFigure 1.3 IoT networking.Presence Protocol), MQTT (Message Queuing Telemetry Transport), AMQP (Advanced Message Queuing Protocol), and 6LoPAN (IPv6 over Low-Power Wireless Personal Area Networks) are basically utilized to establish connectivity between IoT devices in IoT network.RFID stands for Radio Frequency Identification that is used widely in shopping malls as a system whole. RFID system consists of RFID tag, RFID reader, and RFID software. RFID tag is covered by a hard jacket that consists of integrated circuit and antenna and stores digitally encoded data. RFID tags are categorized into Active Tag (own power supply) and Passive Tag (dependent for power supply). RFID reader reads from the tag and transfers data to RFID software for further processes to operate.CoAP, as per its name Constrained Application Protocol [13], is utilized for web transfer just as http but in constrained networks resources environment such as limited computational resources, limited bandwidth and limited power supply in IoT. CoAP in IoT network functions as a session layer and an application layer. CoAP is designed for M2M communication and uses a request-response model for two connected endpoints (objects) in the IoT network.XMPP stands for Extensible Messaging and Presence Protocol [06], an open standard XML (extensible markup language)–based middleware protocol that is used for real-time structured data exchange. XMPP uses decentralized client-server architecture which means the central server is not located for message transfer. So, in this context, XMPP provides flexibility in sustaining interoperability between different things (objects), between diverse systems, and between heterogeneous protocols in the IoT network. XMPP does not support text-based communication.MQTT is a Message Queuing Telemetry Transport protocol [7], publish-subscribe–based ISO