## 4 Application layer
### IoT Connectivity
Long-range technologies are divided into two categories: non-3 GPP standards, i.e., unlicensed technologies, and 3 GPP standards, i.e., licensed technologies [84; 85; 87]. 1. Unlicensed technologies (1) IEEE 802.11 ah (Wi-Fi HaLow): IEEE 802.11 ah technology enhances Wi-Fi by providing greater range and lower power connectivity. Wi-Fi HaLow satisfies the needs of the IoT to enable a range of use cases in commercial, industrial, residential, and public settings. Wi-Fi HaLow supports the low-power connectivity required for applications such as wearables and sensor networks. Its range is longer than many other IoT technology solutions in tough locations where the ability to pass through walls or other barriers is a key factor. It offers a more reliable connection. 2. IEEE 802.11 ax. : Wi-Fi 6 (IEEE 802.11 ax) is the new generation of Wi-Fi technology focusing on efficiency and performance. Wi-Fi 6 technology is all about better and more efficient use of the existing radio frequency medium. It was introduced for video streaming, online gaming, and high-bandwidth applications. 3. Low-power wide-area network (LPWAN): It is becoming increasingly well-liked in the industrial and research communities due to its low-power, long-range, and low-cost communication properties. Rural areas allow for long-distance communication up to 40 km, but in urban areas, it is only 1-5 km. Furthermore, it has a long battery life (over ten years) and is quite affordable. Therefore, IoT applications that send small amounts of data over large distances are ideal for LPWAN. LPWAN is in its infancy, and its maximum capabilitiesand drawbacks will not be visible until the networks are established on a larger scale. Furthermore, the LPWAN currently supports no more than 20% of the people worldwide. This decreased adoption rate impedes LPWAN from being the optimal solution in the upcoming five years. Nevertheless, LPWAN accessibility is rapidly increasing, and by 2022, it is predicted that it will cover 100% of the world's population. Sigfox communication was introduced for the low-cost M2M application areas in which broad coverage is necessary. The Sigfox wireless interface permits any communications with a low power usage level. Therefore, it is optimal for remote devices requiring a power supply for prolonged periods without changing their batteries. It provides a bidirectional capability and is utilized in IoT systems, including the following:  
* Energy-associated communications, such as smart metering. * Transportation, which may include automobile management. * Home and consumer goods. LoRaWAN is another long-range IoT network that is widely used. Lora is a long-range radio wide-area network delivering low-cost mobile security to the IoT, industrial applications, and smart cities. It is designed to save power and support a vast network of devices. Moreover, it is developed to save power and support a vast network of devices. For example, smart street lighting uses the LoRa gateway that employs the LoRaWAN protocol. It can identify signals below the noise level, besides having GPS-free positioning and built-in security. 1. Licensed technologies 1. NB-IoT: NB-IoT is based on narrowband radio technology and is standardized by the third-generation partnership project (3 GPP). Under permitted frequency bands, NB-IoT can coexist with the GSM (global system for mobile communications) and LTE (long-term evolution) (e.g., 700 MHz, 800 MHz, and 900 MHz). The frequency band NB-IoT has a span of 200 KHz [87]. With a high data rate and low latency, narrowband IoT (NB-IoT) is a long-range communication technology enabling several IoT devices and applications. In addition, NB-IoT is a price-efficient solution with a long battery life and better coverage [87]. 2. LTE CAT 1 and LTE CAT 4: Both are popular LTE IoT communication technologies. The key difference between LTE Cat 4 and LTE Cat 1 is their data transmission rate and prices.