The ’Internet of’ series of technologies has been an idea that has been developing over time for many different avenues and purposes. In today’s society, most of the new evolution of technologies are typically part of this thought process, whether its Internet of People (Human-Machine Interaction), Internet of Agents (Machine Learning and Artificial Intelligence), Internet of Content (Cloud) or Internet of Things (Machine-to-Machine Interaction) [
2]. While the authors in [
2] looked at the overall ’Internet of’ series, the one we will focus on will be the Internet of Things. The idea of Internet of Things is essentially when multiple devices, or otherwise known as "Things," are connected together in some manner through the use of a wireless network of some sort. This network can be any wireless protocol such as Bluetooth, WiFi, 5G, Ultra-wideband, radio frequency identification, and many more. Now, all these devices communicate with each other, send data to each other, and are typically used to make things smarter [
2,
3,
4]. Some of the uses of IoT are seen in technology found in cities, homes, transportation, military, agriculture, and so many more. The idea is to make life easier for people who use technology by making the technology smarter. However, all IoT use cases generally fall within the general multilayer architecture ranging from three to six layers, with the four-layer model being the most popular. The five-layer architecture, as shown in
Figure 1, is one that we will focus on in this investigation, as it goes a bit deeper compared to the four-layer model[
1].
The five-layer architecture consists of the perception layer, which is the layer that gathers the data. This can consist of sensors and other things that are used to collect information, such as barcodes [
1]. We then move up a layer to the network access layer, which is essentially the means of communication. This is how the device sends out signals and communicates with other devices. This can be seen as wireless protocols such as ultra-wideband, WiFi, Bluetooth, etc. and helps to create the sensor network [
1]. We then have the ’Network Transmission Layer’ above that, which is how the network communicates with each other as a whole. This can be seen as communication using satellites, mobile communication networks, or even a specific dedicated network [
1]. The next layer would be the Application Support Layer which consists of middleware, cloud platforms, application host, etc. [
1]. And finally, we have the "Presentation Layer" which is what IoT devices are used solely for whether it is used for a smart city, agriculture, transportation, and many more [
1]. In other words, the presentation layer is the output layer for IoT devices where they act upon the world or environment.
2.6. Commonly Used Protocols:
Along with the evolution of IoT devices, many protocols were developed to satisfy the needs of different IoT applications. There are many different situations and needs that come with IoT devices. Some devices need protocols that are energy efficient and short-range, some need different data rates, and some require long-range and high-speed data transport, depending on the use case. This section will give a brief introduction to some of the more common protocols as well as some of the least common protocols that you can find within IoT devices.
ZigBee is a wireless networking protocol based on the IEEE 802.15.4 technical standard [
15]. It has a low data rate, low power consumption, low cost, and encrypted communication using the Advanced Encryption Standard (AES) with a 128-bit key. ZigBee is a great technology for Internet of Things devices that need long battery life and a low data transfer rate. The ZigBee data rate is 250 kbps at 2.4GHz (global), 40 kbps at 915MHz (Americas), and 20 kbps at 868MHz (Europe). Some applications of ZigBee can be found in Smart homes, Smart buildings, the Internet of Medical Things (IoMT), and more [
16,
17].
Dash7 (D7AP) is an open-source subGHz wireless sensor and actuator network protocol (WSAN) that complies with the ISO/IEC 18000-7 standard. It has a medium range of up to 2 Km, low power consumption (multi-year battery life), low latency, and is encrypted using AES with a 128-bit key. D7AP operates in unlicensed ISM bands of 433.92, 868 and 915 MHz [
18,
19]. A few use cases of D7AP can be found in agriculture IoT, IoMT and smart cities [
20].
WiFi, or IEEE 802.11, is a standard of wireless LAN technology widely used in business and home environments to obtain fast and reliable Internet access. WiFi provides a common platform to connect various devices, from smart home applications to industrial sensors. The range, reliability, and security strengths of WiFi are ideal for many IoT applications [
21]. WiFI encryption has evolved in recent years, and each new generation provides stronger security against attacks. WEP was the original WiFi security protocol, which used the RC4 algorithm with two sides of data communication. However, WEP is easily cracked, and it is no longer considered secure. WPA was an improved version of WEP and addressed some of the security vulnerabilities in WEP. WPA2 is the successor to WPA and is considered to be more secure. WPA2 uses the Advanced Encryption Standard (AES) cipher [
22]. WPA3 is the latest WiFi security protocol, offering the strongest security to date. WPA3 uses the Simultaneous Authentication of Equals (SAE) protocol, designed to be more secure than the four-way handshake used in WPA2 [
23]. IEEE 802.11 is a living standard and new generations are being developed regularly to meet the growing demands of wireless networking. Some of the most used IEEE 802.11 standards are IEEE 802.11g, which operates in the 2.4 GHz band and supports data rates up to 54 Mbps; IEEE 802.11n, which operates in the 2.4 GHz and 5 GHz bands and supports data rates up to 600 Mbps.; IEEE 802.11ac, which operates in the 5 GHz band and supports data rates up to 6.93 Gbps; IEEE 802.11ax, which operates in the 2.4 GHz and 5 GHz bands and supports data rates up to 9.6 Gbps [
24,
25].
Cellular networks have been around for a while. With new advancements and technologies being developed around them, new cellular networks were discussed, tested, and created to provide the best performances that will match the needs of the latest technology standard. LTE-Advanced(4G) and 5G technologies are the most recent and widely used cellular standards [
26]. LTE-A (Long-Term Evolution Advanced) is a wireless cellular technology that significantly improved speed, capacity, and coverage over previous generations of cellular technology. It has a peak downlink data rate of 1 Gbps and an uplink data rate of 500 Mbps, a peak downlink spectrum efficiency of 30 bps / Hz and an uplink spectrum efficiency of 15 bps/Hz, and a bandwidth of 100 MHz [
27]. LTE-A is currently being overtaken by 5G [
28]. 5G is the fifth generation of wireless cellular technology. It has improvements over previous generations of cellular networks, such as higher data rates, lower quality of service (QoS) latency, low interference, and increased capacity. Some of the 5G requirements include a maximum downlink data rate of 20 Gbps and an uplink data rate of 10 Gbps, a maximum downlink spectrum efficiency of 30 bps/Hz and uplink spectrum efficiency of 15 bps/Hz, user plane latency of 4 ms for eMBB and 1 ms for URLLC, control plane latency of 10-20ms, and bandwidth of 100 MHz - 1 GHz [
29]. 5G is the key for advanced IoT applications, such as smart factories, smart hospitals, smart transportation, smart agriculture, smart homes and cities, etc [
29,
30].
6LoWPAN is a networking technology that allows IPv6 packets to be efficiently transmitted over low-power wireless networks, such as those based on the IEEE 802.15.4 standard. It supports various mesh network topologies and can fragment and reassemble packets as needed. 6LoWPAN implementations are small enough to fit 32K flash memory parts. 6LoWPAN enables low-power mesh and sensor networks to take advantage of the benefits of IP networking [
31,
32]. It has frequency bands of 2.4 GHz, 868 MHz, and 915 MHz (the same as ZigBee) and data rates between 50 and 250 kbit/s [
33].
Bluetooth is a technology standard used for short-range wireless communication between mobile devices. Bluetooth operates on 79 different frequencies to transmit data from 2.402 GHz to 2.48 GHz and a range up to 100 m (330 ft). The bit rates for Bluetooth are 1 Mbps and 2 Mbps [
34]. It is very useful for transmitting small fragments from different IoT sensors [
35].
Bluetooth Low Energy (BLE) is a wireless technology that is designed to complement both classic Bluetooth and the lowest power wireless technology possible. It is a distinct technology with different design goals and market segments than classic Bluetooth. BLE transmits data over 40 channels in the 2.4 GHz band (2.402 to 2.48 GHz) [
36]. It can be used to create different types of network, from simple point-to-point connections to complex mesh networks. This flexibility makes BLE work with a wide range of applications, including the Internet of Things [
37].
LoRa is an unlicensed band physical layer technology that transmits data transmit signals in the subGHz ISM band. LoRa allows low-data-rate long-range, low-power wireless communication. LoRa has a range of up to 15 km in rural areas and up to 5 Km in urban areas, with data rates of 0.3 kbps - 50 kbps in Europe and 0.9 kbps - 50 kbps in the US [
38] [
39]. LoRaWAN is an open standard that was developed on top of LoRa. It consists of an end device, gateway, network server, and application server. LoRaWAN sits on the data link layer and provides a complete solution by adding a network layer that includes features such as security, authentication, and data routing [
20].
Sigfox is a low-power wide area network (LPWAN) technology designed for the Internet of Things. It uses ultra-narrowband technology to transmit data with a very low power consumption over long distances [
40]. It operates in the 862 - 928 MHz frequency band and has a channel bandwidth of 100 Hz [
41]. With a range of up to 50 km in rural areas and up to 10 km in urban areas, Sigfox can work well with applications that require long-range communication with battery-powered devices. Its data rate ranges from 100 to 600 Bps, depending on the region [
29,
42].
NB-IoT is a low-cost, low-power, and low-data-rate cellular technology built from LTE functions; therefore, it uses the same infrastructure as cellular networks, which makes it a scalable and reliable technology that can be deployed in a variety of locations. It has a range of up to 15 Km in rural areas and 1-5 Km in urban areas, a data rate up to 250 Kbps, and a 200 KHz bandwidth [
20,
43].
Near Field Communication (NFC) is a short-range wireless communication protocol used by mobile devices to do all kinds of applications, such as payments, digital keys for homes and cars, and data transferring. NFC provides secure communication between various devices. It has a short range of 4-10 cm, a data rate of 0.02-0.4 Mbps, and it runs on a 13.56 MHz spectrum [
44]. NFC is used to enhance different IoT solutions with short-range capabilities [
45].
Z-Wave is a subGHz wireless communication protocol used by different IoT applications. It is an ultra-low-power, mesh network protocol that lets devices communicate with each other over long distances (has a range of 100 meters). Its data rates are 9.6 kbps, 40 kbps, or 100 kbps, and it uses a frequency of 908.42 MHz [
46]. Z-Wave deployments can be scaled by linking together Z-Wave networks. Z-Wave is well suited for applications that require reliable, secure, and low-power communication, such as control smart home devices (lights, locks, thermostats, and security systems) [
47].
Li-Fi is a bidirectional short-range wireless technology that uses a visible light communication (VLC) system for data transmission to transfer and receive data. Li-Fi uses overhead LED lighting commonly found in homes as a means of transport and a photo-diode for decoding data. It has a maximum speed of 224 Gbps, which allows a high-definition video to be downloaded in seconds. Because Li-Fi is reliable in light use, it is limited in range since light cannot pass through objects, which makes Li-Fi effective only in closed spaces [
48]. Even though its range limitation could be seen as a problem, this limitation provides an additional layer of security by keeping data away from leaking into public spaces, giving malicious actors access to your network [
49,
50].
Ultra wideband is a short-range, high-bandwidth and energy-efficient wireless communication protocol that can be used for radar imaging, sensor data collection, precise location and tracking. UWB operates at frequencies 3.1 to 10.6 GHz, has a bandwidth of 500 MHz, and a data rate of up to 1 Gbps [
51,
52]. UWB can be used to accurately measure the distance between two devices. This information can be used for a variety of IoT applications [
53].
Advanced Message Queuing Protocol (AMQP) is a reliable and versatile M2M binary protocol. It offers two levels of QoS for the delivery of messages, uses TCP as a transport protocol, and uses TLS/SSL & SASL for security, making it a good fit for high-bandwidth, reliable and secure networks [
54]. It supports various messaging patterns, including request/response, publish/subscribe, and transactions (allowing multiple messages to be sent and received as a single unit of work) and topic-based publish-and-subscribe messaging (allows messages to be published to topics so that subscribers can receive messages that are relevant to them) [
55].
Constrained Application Protocol (CoAP) is a lightweight M2M binary protocol with a fixed header of 4 bytes and small message payloads from the IETF CoRE Working Group designed for constrained IoT devices. It supports both request-response and resource-observe architectures and can be used to interoperate with HTTP and the RESTful Web API [
56]. CoAP uses UDP as a transport protocol and DTLS for security, making it efficient for use on low-bandwidth and unreliable networks. It is designed to be as lightweight as possible, making it suitable for use on constrained devices with limited resources [
54].
The Message Queuing Telemetry Transport Protocol (MQTT) is a publish/subscribe messaging protocol used for lightweight machine-to-machine (M2M) communications in constrained networks. MQTT uses the Transmission Control Protocol (TCP) as its transport protocol that guarantees the delivery of messages. MQTT also uses TLS/SSL for security, which encrypts messages to protect them from unauthorized access. MQTT supports three levels of QoS, making it more reliable when delivering messages. It uses a small amount of bandwidth and processing power. This makes it ideal for use with small devices that have limited resources. MQTT is also suited for large networks because it can efficiently handle a large number of devices. This is because it uses a publish/subscribe model, which allows devices to receive only messages that are relevant to them [
54].
Data Distribution Service (DDS) is a machine-to-machine protocol developed by the Object Management Group (OMG) that features decentralized nodes of clients throughout a system (nodes can identify themselves as subscribers or publishers through a localization server). DDS was created to overcome the disadvantages of centralized publish-subscribe architectures. Provides many quality-of-service parameters that allow users to control the behavior of the DDS system, such as improved scalability, increased reliability, reduced latency, bandwidth, and enhanced security (provides authentication, access control, confidentiality, and integrity to the information distribution) [
57,
58].