# Recent Advances in Evolving Computing Paradigms: Cloud, Edge, and Fog Technologies
## 4 Challenges and Opportunities  
Despite the fact that cloud computing has been around for a long time, it still confronts problems. Cloud security, privacy, confidentiality, availability [122], and sustainability [123] are among them. The dependability of cloud services is an issue as well; when a limited number of data centers offer critical functions, it might be disastrous if one of the data centers goes down [124]. Cloud data centers require immense energy to operate, which requires mitigating energy usage by resource provision optimization policies. The cloud networking infrastructure faces challenges pertaining to network utilization, data congestion, cloud federation [125], etc. As the IoT devices arrived, an emphasis was placed on reducing energy and resource usage, and critical difficulties included increasing the battery life or optimizing the energy utilization of smart devices [126]. The security of IoT devices and withholding the privacy of sensitive data collected by the connected devices pose unique challenges [127]. The availability, reliability, scalability, and interoperability of IoT networks are labelled to be challenging. Edge computing, which moves computation to the network's edge, poses a number of complications, such as focusing on the programmability of edge devices, naming schemes for a large number of edge devices, including security, privacy, data abstraction, service management, and optimization issues [41]. With fog computing still in its developmental stage, it faces many open challenges. It has difficulties similar to edge computing due to its correlations, and the notable challenges include programmability, managing heterogeneous systems, providing security, interoperability, mobility, scalability, federation, and energy/resource efficiency [20; 128]. Fog computing is a more generic model compared to related paradigms due to the far-reaching scope and presence in the Thing-to-Cloud continuum. The comparison and features of the fog, edge and cloud [129; 130; 131; 2, 132] are displayed in Tables 3 and 4. The association between cloud, edge, and fog computing [132] is shown in Figure 12. Fog computing is imminent of offering amelioration in the near future in an open-standards setting of connected devices, apparent when the IEEE Standard adopted the Open-Fog Reference Architecture [133]. Hence, our cynosure for the rest of the paper is on challenges and future research directions pertaining to fog computing. Figure 12: Cloud, fog, and edge computing alliance. \begin{table}
\begin{tabular}{l c c c} \hline \hline
**Feature** & **Fog** & **Edge** & **Cloud** \\ \hline Heterogeneity support & Yes & Yes & Yes \\ Connection to cloud & Yes & Yes or No & Yes \\ Infrastructure need & Yes & Yes & Yes \\ Geographically distributed & Yes & Yes & No \\ Virtualization technology & Yes & No & Yes \\ Location awareness & Yes & Yes & No \\ Ultra-low latency & Yes & Yes & No \\ Scalability & Yes & Yes & Yes \\ Mobility support & Yes & Yes & No \\ Application support—real-time & Yes & Yes & No \\ Application support—large-scale & Yes & Yes & Yes \\ Application support—large-scale & Yes & Yes & Yes \\ Standardized & Yes & Yes & Yes \\ Multiple IoT applications & Yes & No & Yes \\ Data persistence & Yes & No & Yes \\ Computation migration & Yes & No & No \\ Conserving energy & Yes & Yes & No \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Fog, edge, and cloud computing functionalities.