# Fog Computing Enabling Industrial Internet of Things: State-of-the-Art and Research Challenges
## 4 Protocols/Algorithms
### Routing  
[PERSON] et al. [42] have introduced redundant fog loops for WSNs. The proposed fog loop-based scheme has two main steps. Creation of fogs using loop paths is the first step, while the second mechanism creates fog nodes in the source node areas along with many other interfering fogs within the network. This proposed scheme has helped in finding the exact location of the source node in terms of energy efficiency and privacy. Results were compared to the efficiency offered by the Phantom Routing Scheme (PRS). The proposed scheme gives improved efficiency by 4 folds and can also improve the privacy and security up to 8 folds. Since fog computing lowers latency and offers energy saving, they are tailor-made for dealing with WSNs [43]. Sensors in WSNs are resource-constrained, therefore energy efficiency is an important issue. It needs to be addressed for the network to increase network life-time of operation and working efficiently for a prolonged period of time. Sensors in a form of clusters collected data and send to the base station using energy-efficient routing protocols. In this approach, using multi-hop communication, data is transferred to the sink/destination node. The nodes acting as a cluster head are used for multi-hop communications. For networking, apart from the routing problem, another issue that needs to be catered is increasing network lifetime. Network lifetime can be effectively increased by optimizing energy and power consumption at nodes. Some examples of these routing protocols are Low-Energy-Adaptive-Clustering-Hierarchy (LEACH) and Stable-Election-Protocol (SEP). LEACH protocol involves Deterministic Cluster Selection Head and abbreviated as LEACH-DCHS [44]. [PERSON] et al. [45] have proposed LEACH in which rotation of the cluster heads in a randomized manner is used for energy distribution to the nodes evenly. These algorithms haven't been used for fog computing yet, but can be used in future incorporating fog computing. SEP was proposed by [PERSON] et al. [46], prolongs the period of stability of wireless sensor networks. A modified version of SEP (M-SEP) proposed by [PERSON] et al. [47] is suitable for heterogeneous WSNs. Some of the nodes in this approach might have a greater chance of getting selected as a cluster head and have more energy. Moreover, in large WSNs, the data to be processed from heterogeneous devices is in large volumes. Processing time is significantly large, so an alternate approach is to use fog computing. The time required to process large amount of data gets considerably reduced using fog as the sensors in the network get interconnected with the Internet in order to make smart by making them autonomous in making decisions. Another routing protocol that is energy-efficient named as new-SEP is proposed by [PERSON] et al. [48], prolongs the stability of sensor networks supported by fog more than SEP. Optimal clustering nodes are elected by considering various sensor node features such as the ratio of heterogeneity in the network, residual energy, distance between cluster heads. Results were compared with baseline schemes of LEACH and SEP, the proposed scheme performs better in terms of energy-preservation and network lifetime. Considering increasing the network's stability periods, N-SEP performs better than LEACH (50 percent) and SEP (25 percent). An efficient route optimization algorithm was presented in [49] to address the mobility control issue in fog-based SDN networks. The proposed SDN-enabled fog computing architecture had three-layered structure namely, fog layer, network layer and application layer. Results showed that there is a great improvement in network performance. A three-layered plane architecture was proposed to generate efficient routing paths by the authors in [50] for data-center-based heterogeneous networks, using tensor decomposition methods.