# Resource Management in SDN-Based Cloud and SDN-Based Fog Computing: Taxonomy Study
## 6 Open Issues  
Open issues related to SDN cloud and SDN fog, which are derived from a deep analysis of the above-mentioned reviewed researches, are listed as follows:  
1. Power savings is a challenge, along with several related issues such as data transferring, powered devices, and energy wastage.
2. There is a great concentration on the limited number of metrics (Tables 3 and 4) when evaluating the network performance. On the other hand, power consumption is a major metric in power optimization algorithms, but other important measures of network performance are being neglected.
3. The network performance can be enhanced by considering the awareness of the resources management algorithm and considering the bandwidth due to its impact on the overall performance. Moreover, control over resources leads to performance improvement.
4. There has been always a tradeoff relationship between the network performance and power optimization due to the consequences resulting from overutilized and underutilized resources. Only few researches manage to find a balanced relationship between the two variables.
5. Dynamic deterministic of the overall objective from a set of objectives, such as the minimizing delay or maximizing reliability, based on the application type is an open issue.
6. Most research focused on the Central Processing Unit (CPU) as the most dominant factors in energy consumption. Even though it is considered as a high-power consumer element in PM, but other important factors are being neglected, such as RAM, network card, and storage.
7. Most presented techniques focused only at the server level and ignored the possible contributions on flows/links.
8. From state-of-the-art researches in SDN-based fog, we can observe that interrelated fields are presented such as machine learning and artificial intelligent in order to provide a fully programmed environment, which is a promising approach for future researches.
9. Identifying and fulfilling requests with higher priority prior to low-priority requests is an issue due to the high volume of data transferred among different devices, which results in congested links and, thus, latency.
10. Joining SDN and named data networking (NDN) is a new approach to gain the maximum privilege of both techniques. However, few researches are conducted in this field.
11. Furthermore, SDN cloud is an innovative field, which brings a great opportunity for researchers, since most studies either contribute on the field of cloud or SDN.
12. The scalability issue, which can be classified into two aspects: resources scalability either scaling up or down in the cloud and fog layers and controllers scalability (local and global) to consider their location and number of required controllers.
13. Security is one the main challenges encountered in SDN-Based cloud/fog, including authentication and SDN.
14. Legacy SDN such as OpenFlow forces certain architectures when designing controllers that lead to strict environment for the revolution and development, especially in a fog environment.
15. Only a few contributions regarding the simulation tools and testbed that facilitates the experiments of SDN-based environments.