# Fog Computing Enabling Industrial Internet of Things: State-of-the-Art and Research Challenges
## 3 Industrial Internet of Things Applications and Requirements
### IIoT Applications in Relation to Cloud, Fog and Edge Computing  
All IIoT applications require critical QoS parameters in order to produce benefits in every field. Fog term used in computer science is an extension of cloud architecture which offers services of cloud to edge devices. It is seen as a new cloud or it will replace the cloud in future but it is just an architecture that complements cloud architecture in order to provide solutions for critical applications. Entry points in any network are called edge devices. Entry points are part of second and third layer, it has hardware devices named as switches, routers and WAN devices. Cloud is a centralized solution and fog brings solutions at a distributed level by bringing data storage and its computation near the edge of a network. It allows getting services in the proximity of IoT devices. Fog combines services provided by cloud and IIoT applications; or it enables IIoT applications. Cloud architecture is efficient, beneficial and provides solutions. It offers services after storing data in remote centers from the Internet. These remote data centers face less delay and computation as compared to internet. It saves the cost of physical resources, makes connections more reliable and results in an increase in efficiency and performance. It is a flexible, innovative framework in the networking field. It helps in accessing resources anywhere anytime. Question is why fog architecture is needed when cloud is already the best solution to many issues? There are certain issues and requirements of IoT applications and fog can provide solutions. First and foremost, the low-latency requirement of IIoT applications in every field can be attained effectively. It stores data in the proximity of users. Propagation delay between cloud and users will be reduced; computation delay due to huge data traffic at cloud can be reduced. It supports time-sensitive tasks effectively. Second IoT challenge was using network bandwidth in an optimized manner, fog being in the center of cloud servers and end devices. It helps in less usage of bandwidth; data doesn't have to travel fog-to-cloud distance. Popular content is available at the network edge. This will also result in minimizing cost, lifespan of devices, energy consumption and complexity during every demand which goes on the users-to-cloud path. Security issues can be seen on the fog server; it can act as a proxy-server controller. Privacy and safety of data is another important IIoT devices requirement. Fog helps in monitoring such tasks. Exponential increase in IIoT applications in every field making world a cutting edge technology paradigm. Figure 7 shows both these architectures; cloud computing in which IoT devices are directly connected to data centers and cloud server and fog computing in which fog server is in the middle of cloud and IoT devices. Fog works on network edge which improves speed, computing capabilities and provides distributed and better solutions. Fog has complemented the cloud architecture in many ways. Cloud is a centralized solution while fog can work in both a centralized and decentralized manner. Over large geographical area a group of fog nodes can be monitored and managed in a centralized way. Cloud size is large as compared to fog, as it has massive storage of data from the Internet. Fog size is a flexible parameter that can be altered according to the demand of users. For example, for a vehicle tiny sized fog would be enough while for an institution many small fogs can work in a form of network or may be a large-sized fog would be sufficient. Fog has fewer deployment complexities as compared to the cloud. Similarly, cloud management is tricky and more time taking as compared to a fog because of its flexibility. This flexibility will support mobility in networks. Figure 7: Industry 4.0, IIoT applications versus cloud and fog computing. Because of architecture complexity, the cloud can only be operated by technical experts while fog can be managed and operated by little human effort.