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Smart objects are any physical objects that contain embedded technology to sense and/or interact with their environment in a meaningful way by being interconnected and enabling communication among themselves or an external agent
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Smart objects are any physical objects that contain embedded technology to sense and/or interact with their environment in a meaningful way by being interconnected and enabling communication among themselves or an external agent. Some of the fundamental building blocks of IoT networks are Sensors Actuators Smart Objects Sensors: A sensor does exactly as its name indicates: It senses. A sensor measures some physical quantity and converts that measurement reading into a digital representation.
into useful data that can be consumed by intelligent devices or humans. Sensors are not limited to human-like sensory data. They are able to provide an extremely wide spectrum of rich and diverse measurement data with far greater precision than human senses. Sensors provide superhuman sensory capabilities. Sensors can be readily embedded in any physical objects that are easily connected to the Internet by wired or wireless networks, they can interpret their environment and make intelligent decisions. Sensors have been grouped into different categories Active or passive: Sensors can be categorized based on whether they produce an energy output and typically require an external power supply (active) or whether they simply receive energy and typically require no external power supply (passive). Invasive or non-invasive: Sensors can be categorized based on whether a sensor is part of the environment it is measuring (invasive) or external to it (non-invasive). Contact or no-contact: Sensors can be categorized based on whether they require physical contact with what they are measuring (contact) or not (no-contact). Absolute or relative: Sensors can be categorized based on whether they measure on an absolute scale (absolute) or based on a difference with a fixed or variable reference value (relative). Area of application: Sensors can be categorized based on the specific industry or vertical where they are being used. How sensors measure: Sensors can be categorized based on the physical mechanism used to measure sensory input (for example, thermoelectric, electrochemical, piezoresistive, optic, electric, fluid mechanic, photoelastic). What sensors measure: Sensors can be categorized based on their applications or what physical variables they measure. The physical phenomenon a sensor is measuring is shown in Table-2.
A fascinating use case to highlight the power of sensors and IoT is in the area of precision agriculture (sometimes referred to as smart farming), which uses a variety of technical advances to improve the efficiency, sustainability, and profitability of traditional farming practices. This includes the use of GPS and satellite aerial imagery for determining field viability; robots for high-precision planting, harvesting, irrigation, and so on; and real-time analytics and artificial intelligence to predict optimal crop yield, weather impacts, and soil quality. Different types of sensors in a smart phone is shown in figure 2.
Actuators: Actuators are natural complements to sensors. Figure 2.2 demonstrates the symmetry and complementary nature of these two types of devices. Sensors are designed to sense and measure practically any measurable variable in the physical world. They convert their measurements (typically analog) into electric signals or digital representations that can be consumed by an intelligent agent (a device or a human). Actuators, on the others hand, receive some type of control signal (commonly an electric signal or digital command) that triggers a physical effect, usually some type of motion, force, and so on. Actuators are natural complements to sensors. Figure 2.2 demonstrates the symmetry and complementary nature of these two types of devices. Sensors are designed to sense and measure practically any measurable variable in the physical world. They convert their measurements (typically analog) into electric signals or digital representations that can be consumed by an intelligent agent (a device or a human). Actuators, on the others hand, receive some type of control signal (commonly an electric signal or digital command) that triggers a physical effect, usually some type of motion, force, and so on. Figure 2.2 : How Sensors and Actuators Interact with the Physical World Much like sensors, actuators also vary greatly in function, size, design, and so on. Some common ways that they can be classified include the following: Type of motion: Actuators can be classified based on the type of motion they produce (for example, linear, rotary, one/two/three-axes). Power: Actuators can be classified based on their power output (for example, high power, low power, micro power) Binary or continuous: Actuators can be classified based on the number of stable- state outputs. Area of application: Actuators can be classified based on the specific industry or vertical where they are used.
Different types of Actuators are presented in Table -2. Table -2.2: Actuator Classification by Energy Type Micro-Electro-Mechanical Systems (MEMS) Micro-electro-mechanical systems (MEMS referred to as micro-machines, can integrate and combine electric and mechanical elements, such as sensors and actuators, on a very small (millimeter or less) scale. The combination of tiny size, low cost, and the ability to mass produce makes MEMS an attractive option for a huge number of IoT applications. Ex: Inkjet printers use micropump MEMS. Smart phones also use MEMS technologies for things like accelerometers and gyroscopes Smart Objects Smart objects are, quite simply, the building blocks of IoT. They are what transform everyday objects into a network of intelligent objects that are able to learn from and interact with their environment in a meaningful way. A smart object , is a device that has, at a minimum, the following four defining characteristics Processing Unit: A smart object has some type of processing unit for acquiring data, processing and analyzing sensing information received by the sensor(s), coordinating control signals to any actuators, and controlling a variety of functions on the smart object, including the communication and power systems. Sensor(s) and /or actuator(s): A smart object is capable of interacting with the physical world through sensors and actuators. A smart object does not need to contain both sensors and actuators. In fact, a smart object can contain one or multiple sensors and/or actuators, depending upon the application. Communication Device: The communication unit is responsible for connecting a smart object with other smart objects and the outside world (via the network). Communication devices for smart objects can be either wired or wireless. Power Source: Smart objects have components that need to be powered. Interestingly, the most significant power consumption usually comes from the communication unit of a smart object. Trends in Smart Objects:
Limited transmission speeds Limited power These limitations greatly influence how WSNs are designed, deployed, and utilized. Figure 2.3 below shows an example of such a data aggregation function in a WSN where temperature readings from a logical grouping of temperature sensors are aggregated as an average temperature reading. Figure 2.3 Data Aggregation in Wireless Sensor Networks These data aggregation techniques are helpful in reducing the amount of overall traffic (and energy) in WSNs with very large numbers of deployed smart objects. Wirelessly connected smart objects generally have one of the following two communication patterns: Event-driven: Transmission of sensory information is triggered only when a smart object detects a particular event or predetermined threshold. Periodic: Transmission of sensory information occurs only at periodic intervals. Communication Protocols for Wireless Sensor Networks: Any communication protocol must be able to scale to a large number of nodes. Likewise, when selecting a communication protocol, you must carefully take into account the requirements of the specific application. Also consider any trade-offs the communication protocol offers between power consumption, maximum transmission speed, range, tolerance for packet loss, topology optimization, security, and so on. Sensors often produce large amounts of sensing and measurement data that needs to be processed. This data can be processed locally by the nodes of a WSN or across zero or more hierarchical levels in IoT networks. IoT is one of those rare technologies that impacts all verticals and industries, which means standardization of communication protocols is a complicated task, requiring protocol definition across multiple layers of the stack, as well as a great deal of coordination across multiple standards development organizations.
The characteristics and attributes considered when selecting and dealing with connecting smart objects are 1)Range: It defines how far does the signal need to be propagated? That is, what will be the area of coverage for a selected wireless technology? The below figure 2.4 shows the range considered Figure 2.4 Wireless Access Landscape Short Range: o The classical wired example is a serial cable. o Wireless short-range technologies are often considered as an alternative to a serial cable, supporting tens of meters of maximum distance between two devices. o Examples of short-range wireless technologies are IEEE 802.15.1 Bluetooth and IEEE 802.15.7 Visible Light Communications (VLC). o These short-range communication methods are found in only a minority of IoT installations. Medium Range: o In the range of tens to hundreds of meters, many specifications and implementations are available. o The maximum distance is generally less than 1 mile between two devices. o Examples of medium-range wireless technologies include IEEE 802.11 Wi- Fi, IEEE 802.15.4, and 802.15.4g WPAN. o Wired technologies such as IEEE 802.3 Ethernet and IEEE 1901. o Narrowband Power Line Communications (PLC) may also be classified as medium range, depending on their physical media characteristics. Long Range : o Distances greater than 1 mile between two devices require long-range technologies. Wireless examples are cellular (2G, 3G, 4G) and some applications of outdoor IEEE 802.11 Wi-Fi and Low-Power Wide-Area (LPWA) technologies.
Topology Among the access technologies available for connecting IoT devices, three main topology schemes are dominant: star, mesh, and peer-to-peer. For long-range and short-range technologies, a star topology is prevalent, as seen with cellular, LPWA, and Bluetooth networks. Star topologies utilize a single central base station or controller to allow communications with endpoints. For medium-range technologies, a star, peer-to-peer, or mesh topology is common. Peer-to-peer topologies allow any device to communicate with any other device as long as they are in range of each other. Peer-to-peer topologies enable more complex formations, such as a mesh networking topology. The figure 2.5 below represents the various topology. Figure 2.5 Star, Peer-to-Peer, and Mesh Topologies The disadvantage of sub-GHz frequency bands is their lower rate of data delivery compared to higher frequencies. Example: Indoor Wi-Fi deployments are mostly a set of nodes forming a star topology around their access points (APs). Outdoor Wi-Fi may consist of a mesh topology for the backbone of APs, with nodes connecting to the APs in a star topology. IEEE 802.15.4 and 802.15.4g and even wired IEEE 1901.2a PLC are generally deployed as a mesh topology. Mesh topology requires the implementation of a Layer 2 forwarding protocol known as mesh-under or a Layer 3 forwarding protocol referred to as mesh-over on each intermediate node.
Constrained Devices: Constrained nodes have limited resources that impact their networking feature set and capabilities. Constrained nodes can broken down into different classes such as shown in Table 2.3: Table 2.3 Classes of Constrained Nodes, as Defined by RFC 7228 Constrained-node networks are often referred to as low-power and lossy networks (LLNs). Lossy networks indicates that network performance may suffer from interference and variability due to harsh radio environments. Layer-1 and Layer-2 protocols that can be used for constrained-node networks must be evaluated in the context of the following characteristics for use-case applicability: data rate and throughput, latency and determinism, and overhead and payload. The IoT access technologies developed for constrained nodes are optimized for low power consumption, but they are also limited in terms of data rate, which depends on the selected frequency band, and throughput. The data rates available from IoT access technologies range from 100 bps with protocols such as Sigfox to tens of megabits per second with technologies such as LTE and IEEE 802.11ac. Short-range technologies can also provide medium to high data rates that have enough throughput to connect a few endpoints. On constrained networks, latency may range from a few milliseconds to seconds, and applications and protocol stacks must cope with these wide-ranging values. For example, UDP at the transport layer is strongly recommended for IP endpoints communicating over LLNs When considering constrained access network technologies, it is important to review the MAC payload size characteristics required by applications.
Table 2.4 Protocol Stacks Utilizing IEEE 802.15. ZigBee: It is an IoT solution for interconnecting smart objects. ZigBee solutions are aimed at smart objects and sensors that have low bandwidth and low power needs. The Zigbee specification has undergone several revisions. In the 2006 revision, sets of commands and message types were introduced, and increased in number in the 2007 (called Zigbee pro) iteration, to achieve different functions for a device, such as metering, temperature, or lighting control. These sets of commands and message types are called clusters. Ultimately, these clusters from different functional domains or libraries form the building blocks of Zigbee application profiles. Vendors implementing pre-defined Zigbee application profiles like Home Automation or Smart Energy can ensure interoperability between their products. The main areas where ZigBee is the most well-known include automation for commercial, retail, and home applications and smart energy. In the industrial and commercial automation space, ZigBee-based devices can handle various functions, from measuring temperature and humidity to tracking assets. For home automation, ZigBee can control lighting, thermostats, and security functions. ZigBee Smart Energy brings together a variety of interoperable products, such as smart meters, that can monitor and control the use and delivery of utilities, such as electricity and water. The traditional ZigBee stack is illustrated in the below figure 2.6.
Figure 2.6 High-Level ZigBee Protocol Stack The ZigBee network and security layer provides mechanisms for network startup, configuration, routing, and securing communications. This includes calculating routing paths in what is often a changing topology, discovering neighbors, and managing the routing tables as devices join for the first time. The network layer is also responsible for forming the appropriate topology, which is often a mesh but could be a star or tree as well. From a security perspective, ZigBee utilizes 802.15.4 for security at the MAC layer, using the Advanced Encryption Standard (AES) with a 128-bit key and also provides security at the network and application layers. ZigBee is one of the most well-known protocols built on an IEEE 802.15. foundation. On top of the 802.15.4 PHY and MAC layers, ZigBee specifies its own network and security layer and application profiles. ZigBee IP ZigBee IP was created to embrace the open standards coming from the IETF’s work on LLNs, such as IPv6, 6LoWPAN, and RPL They provide for low-bandwidth, low- power, and cost-effective communications when connecting smart objects. ZigBee IP is a critical part of the Smart Energy (SE) Profile 2.0 specification from the ZigBee Alliance. SE 2.0 is aimed at smart metering and residential energy management systems. Any other applications that need a standards-based IoT stack can utilize Zigbee IP. The ZigBee IP stack is shown in below figure 2.7. Figure 2.7 ZigBee IP Protocol Stack ZigBee IP supports 6LoWPAN as an adaptation layer. ZigBee IP requires the support of 6LoWPAN’s fragmentation and header compression schemes At the network layer, all ZigBee IP nodes support IPv6, ICMPv6, and 6LoWPAN Neighbor Discovery (ND), and utilize RPL for the routing of packets across the mesh network. 802.15.4 Physical and MAC Layer: The 802.15.4 standard supports an extensive number of PHY options that range from 2.4 GHz to sub-GHz frequencies in ISM bands. The original IEEE 802.15.4-2003 standard specified only three PHY options based on direct sequence spread spectrum (DSSS) modulation.
o The MAC layer achieves these tasks by using various predefined frame types. In fact, four types of MAC frames are specified in 802.15.4: o Data frame: Handles all transfers of data o Beacon frame: Used in the transmission of beacons from a PAN coordinator o Acknowledgement frame: Confirms the successful reception of a frame o MAC command frame: Responsible for control communication between devices Each of these four 802.15.4 MAC frame types follows the frame format shown in Figure 2.9. In Figure 2.9, notice that the MAC frame is carried as the PHY payload. The 802.15.4 MAC frame can be broken down into the MAC Header, MAC Payload, and MAC Footer fields. Figure 2.9IEEE 802.15.4 MAC Format The MAC Header field is composed of the Frame Control, Sequence Number and the Addressing fields. The Frame Control field defines attributes such as frame type, addressing modes, and other control flags. The Sequence Number field indicates the sequence identifier for the frame. The Addressing field specifies the Source and Destination PAN Identifier fields as well as the Source and Destination Address fields. The MAC Payload field varies by individual frame type. The MAC Footer field is nothing more than a frame check sequence (FCS). An FCS is a calculation based on the data in the frame that is used by the receiving side to confirm the integrity of the data in the frame. Topology IEEE 802.15.4–based networks can be built as star, peer-to-peer, or mesh topologies. Mesh networks tie together many nodes. This allows nodes that would be out of range if trying to communicate directly to leverage intermediary nodes to transfer communications. Every 802.15.4 PAN should be set up with a unique ID. All the nodes in the same 802.15.4 network should use the same PAN ID. Figure 2.10 shows an example of an 802.15.4 mesh network with a PAN ID of 1.
Figure 2.10: 802.15.4 Sample Mesh Network Topology FFD (full-function devices) acts as a PAN coordinator to deliver services that allow other devices to associate and form a cell or PAN. FFD devices can communicate with any other devices, whereas RFD devices can communicate only with FFD devices. Security The IEEE 802.15.4 specification uses Advanced Encryption Standard (AES) with a 128-bit key length as the base encryption algorithm for securing its data. In addition to encrypting the data, AES in 802.15.4 also validates the data that is sent. This is accomplished by a message integrity code (MIC), which is calculated for the entire frame using the same AES key that is used for encryption. The figure 2.11 below shows the IEEE 802.15.4 frame format at a high level, with the Security Enabled bit set and the Auxiliary Security Header field present.
o Multi-Rate and Multi-Regional Offset Quadrature Phase-Shift Keying (MR-O-QPSK): Shares the same characteristics of the IEEE 802.15.4-2006 O- QPSK PHY, making multi-mode systems more cost-effective and easier to design. MAC Layer: The following are some of the main enhancements to the MAC layer proposed by IEEE 802.15.4e-2012: Time-Slotted Channel Hopping (TSCH): TSCH is an IEEE 802.15.4e-2012 MAC operation mode that works to guarantee media access and channel diversity. Channel hopping, also known as frequency hopping, utilizes different channels for transmission at different times. TSCH divides time into fixed time periods, or “time slots,” which offer guaranteed bandwidth and predictable latency. In a time, slot, one packet and its acknowledgement can be transmitted, increasing network capacity because multiple nodes can communicate in the same time slot, using different channels. A number of time slots are defined as a “slot frame,” which is regularly repeated to provide “guaranteed access.” The transmitter and receiver agree on the channels and the timing for switching between channels through the combination of a global time slot counter and a global channel hopping sequence list, as computed on each node to determine the channel of each time slot. TSCH adds robustness in noisy environments and smoother coexistence with other wireless technologies, especially for industrial use cases. Information elements: Information elements (IEs) allow for the exchange of information at the MAC layer in an extensible manner, either as header IEs (standardized) and/or payload IEs (private). Specified in a tag, length, value (TLV) format, the IE field allows frames to carry additional metadata to support MAC layer services. These services may include IEEE 802.15.9 key management, Wi-SUN 1.0 IEs to broadcast and unicast schedule timing information, and frequency hopping synchronization information for the 6TiSCH architecture. Enhanced beacons (EBs): EBs extend the flexibility of IEEE 802.15.4 beacons to allow the construction of application-specific beacon content. This is accomplished by including relevant IEs in EB frames. Some IEs that may be found in EBs include network metrics, frequency hopping broadcast schedule, and PAN information version. Enhanced beacon requests (EBRs): Like enhanced beacons, an enhanced beacon request (EBRs) also leverages IEs. The IEs in EBRs allow the sender to selectively specify the request of information. Beacon responses are then limited to what was requested in the EBR. For example, a device can query for a PAN that is allowing new devices to join or a PAN that supports a certain set of MAC/PHY capabilities. Enhanced Acknowledgement:
The Enhanced Acknowledgement frame allows for the integration of a frame counter for the frame being acknowledged. This feature helps protect against certain attacks that occur when Acknowledgement frames are spoofed. The 802.15.4e-2012 MAC amendment is quite often paired with the 802.15.4g- PHY. Figure 2.11 details this format Figure 2.11: IEEE 802.15.4g/e MAC Frame Format Topology: Deployments of IEEE 802.15.4g-2012 are mostly based on a mesh topology. A mesh topology allows deployments to be done in urban or rural areas, expanding the distance between nodes that can relay the traffic of other nodes. Support for battery-powered nodes with a long lifecycle requires optimized Layer 2 forwarding or Layer 3 routing protocol implementations. This provides an extra level of complexity but is necessary in order to cope with sleeping battery-powered nodes. Security: Both IEEE 802.15.4g and 802.15.4e inherit their security attributes from the IEEE 802.15.4-2006 specification. Therefore, encryption is provided by AES, with a 128-bit key. In addition to the Auxiliary Security Header field initially defined in 802.15.4-2006, a secure acknowledgement and a secure Enhanced Beacon field complete the MAC layer security. Figure 2.12 shows a high-level overview of the security associated with an IEEE 802.15.4e MAC frame.