# Energy Efficiency for Green Internet of Things (IoT) Networks: A Survey +
## 3 Literature Review
### IoT Enabling Technologies  
Enabling technologies play a crucial role in realizing the IoT vision. These technologies provide connectivity, usability, capabilities, etc. that are required to facilitate efficient use of IoT applications [36]. Several studies in the literature have reported the enabling technologies and thus, this section introduces an overview of those technologies which are related to the scope of this paper.  
* Cloud Computing: as the numbers of IoT smart devices increase, the amount of data generated by them also increases [37]. However, IoT devices tend to suffer from limited energy, memory, processing capabilities, etc., and their integration into the cloud is the best available way to overcome most of these issues. Cloud computing is employed to process, store, monitor and visualize the information comes from the IoT devices [38]. This means data processing and storage takes place in the cloud platform rather than on the IoT device [39], this has significant implications for IoT-constrained devices such as low-cost connectivity, scalability, interoperability, etc.
* Hardware Devices: various hardware platforms have been evolved to perform the IoT networks such as Raspberry Pi, NodeMCU (ESP8266), Arduino, BeagleBoard, FriendlyARM, etc. [24]. These devices vary from low-cost, low-power, processing units (e.g., microprocessors, microcontrollers, etc.), single-boards and software applications that can run IoT applications and communicate over the Internet [40,41].
* Wireless Communication: most IoT devices rely on low-power physical networking technologies such as RFID, Bluetooth, WiFi and IEEE standard 802.15.4 which are  
Figure 4: Interactions between IoT networks.  
essential to activate the connectivity between smart devices [42]. These technologies must be globally addressable to connect with other smart devices over the Internet, either directly or indirectly, via an IP address [43].
* Communication Protocol: IoT devices require IPv4 to connect through the Internet; however the near exhaustion of IPv4 addresses prior to the advent of the IoT and the prediction that there will be up to 50 billion Internet-connected devices by 2025 has meant that a replacement is required to permit the continued expansion of the IoT and Internet in general. IPv6 is the standard proposed to replace IPv4, and uses 128-bit addressing, allowing for a total of \(3.4\times 10^{38}\) unique addresses, instead of the 32-bit addressing used for IPv4 [44]. IPv6 has been applied to low-power wireless personal area networks via 6 LoWPAN [45] which allows sensor nodes with limited resources to forward and share their data wirelessly to the other devices/things or cloud infrastructure.
* WSNs: are the most crucial part of the communication process of the IoT networks. They contain sensors embedded with a microcontroller to provide intelligence and a means of communicating via the Internet or some other network [46]. The sensors enable interaction with the physical world [47], and without the associated networks, there would be no communication between the virtual and physical worlds. The benefits of connecting the WSN to the IoT is to provide remote access and permit them to connect and disseminate the information with other devices/systems over the Internet [48].