# An Overview of Fog Data Analytics for IoT Applications
## 5 Research Challenges
### Heterogeneity and Interoperability  
Myriad IoT devices [60] present in the market have a different set of data and interfacing requirements, which poses a great challenge in integrating it with an entire network without incurring the additional cost of computation and hardware. Devices such as thermostats, ambient light sensors, fire and smoke detection sensors, digital voice assistants, smart door locks, and connected media devices induce a large amount of heterogeneity in the network, and data communication between these devices needs a uniform interface.  
\begin{table}
\begin{tabular}{p{56.9 pt} p{56.9 pt} p{56.9 pt} p{56.9 pt} p{56.9 pt}} \hline \hline
**Work** & **Scope** & **Focused Aspects** & **Strength** & **Weakness** \\ \hline [PERSON] et al. [55] & Smart city & Latency, energy consumption & Lower energy consumption, heterogeneous communications between IoT devices & Low scalability, lack of real-time data processing \\ \hline [PERSON] et al. [56] & Smart grid & Network utilization, latency utilization & Context-aware information with reduced latency, better energy and network usage overhead & Lack of resource cost measures, high computational complexity, unevaluated overhead \\ \hline [PERSON] et al. [57] & e-Healthcare & Latency, energy consumption, network utilization & Lowered energy consumption with low response time & Mobility is ignored, latency caused by high computation \\ \hline [PERSON] et al. [42] & Fog implementation with cloudlets & Response time & reduced network latency for SDN & Energy consumption was not evaluated, latency caused by high computation \\ \hline [PERSON] et al. [7] & Robotics application & Power consumption, latency & Modeled battery discharge profiles, reduction in power consumption, low latency & Accuracy was not investigated, low scalability \\ \hline [PERSON] et al. [58] & Mobile application & Response time, energy consumption & Low execution time and low latency, suited for multi-agent architecture & Mobility, privacy, and context awareness were lacking \\ \hline [PERSON] et al. [59] & General & Energy, wait time & Considered gap in the wait time, energy expenditure for different devices, latency & Heterogeneity was not considered, inter-dependency of IoT devices, high computational complexity \\ \hline \hline \end{tabular}
\end{table}
Table 1: Research work on latency sensitivity in different areas.  
Fog nodes solve interfacing issues by abstracting the interfacing complexity and providing a uniform standardized interface for easy communication and real-time data stream sharing. Furthermore, fog node communication protocols should be designed in a way that can cope with future changes. Some protocols proposed in [55; 61] are used for energy-efficient routing and navigation in heterogeneous networks.  
The fog layer could be deployed as distributed fog nodes with someone acting as the controller node for larger system requirements. Here, too, nodes need to be of different types, and they still should work in harmony. In case of failure of the controller node, some other node should act as a controller to handle the operations without any problems and continue to serve connected devices. Devices should be easily connected to the network, and data transmission between different types of devices should be seamless to support the best user experience. In smart homes, most devices are connected to a central wireless network and can be easily operated and controlled with different mobile devices. For example, digital assistance and a stereo system connected with the wireless network are controlled using smartphones or tablets, which should support platform independence and uniform APIs. The heterogeneity of devices can be observed from Figure 7.