Protocols & Enabling Technologies

Generally, standards are important factors for efficient and cost-effective deployment of fog-based IoT systems.
By considering the distributed architecture of the fog-based IoT shown in Figure 1, there are still some challenging issues such as mobility and scalability for heterogeneous devices. In order to support fog-based IoT
applications with this demanding heterogeneous requirement, it is necessary to consider protocols and technologies to support devices that have limited bandwidth and energy. In this section, we explore some of
the most important enabling technologies that can be used for efficient communication of IoT devices in fog based IoT architecture. These technologies and protocols include Radio Frequency Identification (RFID),
Wireless Identification and Sensing Platform (WISP), WSN, Bluetooth Low Energy (BLE), Near Field Communication (NFC), IEEE 802.15.4, IEEE 802.11ah, Z-Wave, Long Term Evolution-Advanced (LTE-A), LoRaWAN, IPv6, IPv6 over Low Power Wireless Personal Area Networks (6LoWPAN), NarrowBand IoT (NB-IoT), and SigFox. In addition, we briefly present some of the available standards such as IEEE Std 1905.1a and IEEE 1451 which are useful to improve interoperability among various technologies, applications, and topologies.

The RFID systems operate on a frequency band of 125 kHz and require a 12 V power supply. They are generally made up of RFID tags and readers. RFID tags use technology to reflect back the radio wave and then pass on the data to the readers [37]. RFID readers can read and extract the stored information inside the RFID tags. RFID-based systems have the ability to pick up tag IDs automatically from a distance without considering
the Line of Sight (LOS) operations. Moreover, they are able to scan multiple items at the same time without the need to scan them independently. They can also scan the tags quickly typically in milliseconds. Two of the most
common applications of RFID-based systems are in commercial stores and hospitals. For instance, for safety monitoring, an RFID bracelet can be attached to a psychiatric patient (e.g. on the hand of the patient). If
the patient attempts to leave the predefined restricted area bypassing the door equipped with an RFID reader, an alarm message can be sent to the staff over the wireless network in order to take immediate action.

Journal Pre-proof WISP is a battery-free and wireless platform used for the purposes of sensing and computation. WISP devices are powered by ultra-high frequency RFID readers. WISP-based systems use the same communication technology as in the RFID-based systems. However, they are unique with a fully programmable microcontroller. In addition, WISP-based cameras can be used for battery-free imaging (e.g. capture and transmit images) by utilizing low-power communication technology and harvesting wireless power [39]. Moreover, WISP has recently attracted too much attention in the area of security and cryptography [40].

WSNs consist of small nodes with sensing capabilities. They can be easily deployed into the existing IoT infrastructures with no (or little) modifications since IoT supports the interoperability of various networks including WSNs. For example, the authors investigated the integration of WSNs into IoT by deploying real-world wireless sensors in order to monitor appliances in a sustainable and energy-efficient smart building. Another attempt to integrate WSNs with IoT is presented in [45] where the sensor nodes collect various environmental parameters such as temperature, humidity, and air quality from the environment and store them on the cloud so that the user can access them universally. Different from the RFID-based systems which need a reader, WSNs communicate in a Peer-to-Peer (P2P) manner. However, based on the configuration and algorithm of the WSNs, sink nodes can be utilized to collect sensed data from the other nodes in the network.

BLE is a wireless technology for short-range communication that operates on the 2.4 GHz frequency band. It can be easily integrated into classic Bluetooth and therefore, can benefit from the use of Bluetooth technology
as well. BLE can be utilized in various IoT scenarios such as in medical monitoring, public transportation systems, and monitoring industrial environments. For example, BLE can be used in industrial and process automation in order to help obtain the data wirelessly from the control room and therefore, facilitates the process of data collection and storage.

NFC [49] has a very short-range communication and operates on a frequency band of 13.56 MHz. This standard enables devices to communicate with each other only in close vicinity (e.g. in the range of about 10 cm). The targets of NFC technology can be simple devices such as stickers and cards. Moreover, it also allows P2P communication in which both devices must be powered. NFC can be used for financial transactions. In addition, other applications benefiting from the NFC are social networking, museums, and mobile ticketing systems.

The IEEE 802.15.4 standard provides low-cost and low-power wireless communication within short ranges (usually up to 20 m) which makes it appropriate for the use in WSNs, Machine-to-Machine (M2M)
communications and IoT. It defines the characteristics of physical and data link layers for Low-Rate Wireless Personal Area Networks (LR-WPANs) products.

The physical layer of the IEEE 802.15.4 standard is responsible for transmitting and receiving data, link quality indication, discovering the levels of energy in the current channel, and clear channel assessment [56]. On the other hand, the data link layer of this standard is responsible for frame validation, channel access mechanism, and acknowledgement of delivered frames as well as beacon management.

IEEE 802.11ah [57] is the competitor standard of IEEE 802.15.4. It is an improvement to the widely utilized IEEE 802.11 standard and uses the frequency band of 900 MHz to provide extended network coverage. The
performance of the IEEE 802.11ah reveals that it performs better than IEEE 802.15.4 in the case of congested networks. However, IEEE 802.15.4 outperforms IEEE 802.11ah in terms of energy consumption.
Moreover, the study shows that the IEEE 802.11ah is suitable for M2M, Vehicle-to-Vehicle (V2V), and IoT applications which require long-range communication and long battery life.

Z-Wave [60] is a low power MAC protocol that operates on the frequency band of 908 MHz and is utilized by small data packets within the range of 30m at low speeds up to 100 kbps. However, it is not suitable for
transmitting or streaming of time-critical data due to its low data rate. The ZWave solution can be Journal Pre-proof extensively used in smart home automation where the protocol runs over various appliances with smart sensors, smart lighting, smart air-conditioning, etc.

LTE-A is the enhanced version of LTE which provides higher throughput and lower latencies as well as improved coverage. It supports higher bandwidth up to 100 MHz aiming to obtain a higher level of system
performance [62]. LTE-A has important characteristics such as carrier aggregation, support for relay nodes, and enhanced use of multi-antenna techniques which make it suitable for the use in fog-based IoT infrastructures. This is because fog-based devices may be used to offer relay services to end-devices or other fog nodes in the network.

LoRaWAN is a Low Power Wide Area (LPWA) technology that supports low power and low data rate (e.g. from 0.3 kbps to 50 kbps) as well as long-range operations. In fog-based IoT, LoRa technology can be used by
end-devices in order to communicate with gateways using a single hop. Moreover, LoRaWAN technology can solve the connectivity problem of billions of smart devices in the IoT era in the next few years .

IPv6 is the Internet protocol introduced to overcome the shortcomings of IPv4. It can handle scalability by providing a unique address to a large number of IoT devices. IPv6 supports Internet Protocol Security (IPSec).
It also offers support for neighbour discovery which enables neighbouring nodes to communicate and determine the presence of each other. These features make IPv6 a suitable protocol for fog-based IoT systems where fog based devices share the information on how to reach each other and how to relay information through the available device. 6LoWPAN is a standard defined to support IEEE 802.15.4 low-power wireless networks in the frequency band of 2.4 GHz [64]. It enables IPv6 connectivity for constrained embedded devices that utilize IEEE 802.15.4 low-power wireless communications.

NB-IoT is a low power cellular technology specifically designed for IoT in order to provide improved coverage with respect to LTE. With NB-IoT, it is possible to connect different objects that need a small amount of data
over long periods. This technology has been utilized in different smart cities’ applications such as intelligent parking and smart hospitals. The integration of NB-IoT and fog computing can save network
bandwidth, ensure the quality of data analysis, improve the response time, and enhance the efficiency of data storage compared to traditional cloud computing models.

SigFox is a network protocol that provides M2MWAN communication solutions that operate on the 868 MHz frequency band. It is specially designed to meet the requirements of massive IoT applications in order to
enhance the network capacity, increase the life cycle of the device, reduce the cost of devices, and improve communication range as well as minimize energy consumption. SigFox is a software-based communication
solution where all the computing tasks are managed in the cloud. SigFox will have better potential in fog-based IoT systems because of the capability of fog-based devices to perform some of the tasks closer to the network edges.

In addition to the abovementioned protocols and technologies, IEEE Std 1905.1a and IEEE 1451 are two available standards that can be utilized to improve interoperability among various technologies, topologies, and
applications in fog-based IoT systems. IEEE Std 1905.1a is a standard that supports a common interface, by defining an abstraction layer, in order to deploy multiple networking technologies at smart homes [69]. The
abstraction layer provides a platform for improving network range, guaranteeing security for network connections, and establishing various network management functionalities such as Quality of Service (QoS)
negotiation, discovery, and path selection. IEEE Std 1905.1a can be easily deployed to fog-based IoT systems with different characteristics such as load balancing, aggregated throughput, self-install, and the support for
simultaneous and multiple streams.

IEEE 1451 [70] is a set of standards developed to integrate various protocols and standards to support interoperability among different applications and technologies. An important characteristic of the IEEE 1451 standard is that Transducer Electronic Data Sheets (TEDS) of all transducers and the data communication on the Journal Pre-proofInternet in the same way for all sensors and actuators regardless of the type of the network which can be either wired or wireless.

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