# A Survey on Intrusion Detection Systems for Fog and Cloud Computing
## 3 Security in Fog Computing  
The fast-growth and numerous big data and IoT applications have generated massive amounts of data required to process and analyze far beyond the traditional computing model. The rationale of fog computing (FC) technology is to tackle the issues of IoT applications in traditional cloud computing models such as ultra-high latency, high bandwidth, and geographic dispersion [17]. FC can be defined, according to the OpenFog Consortium, as a system-level horizontal architecture that distributes computing services, storage, networking functions, and controls to the proximity of data devices [18]. FC acts as an intermediary between the cloud and end-devices, bringing connected devices closer to the networking, storage, and processing services. It is an approach to provide computational and storage services closer to working in real time and closer to the connected devices in the network. FC can be treated as an extension of cloud computing to adapt to IoT data. It supports the computation offloading process and relevant services close to the users, enhancing the computational speed and reducing the burden of traditional cloud computing data centers. This novel computing model provides intelligent services to meet data optimization, privacy, security, and real-time processing requirements, by collaborating with cloud computing and mobile edge network infrastructure.  
In the FC system, resources located at both core and edge can be employed for computing. It works based on the concept of decentralized computing to boost computational speed. In most FC models, the computational power is focused on the LAN resources further away from the network's core and closer to the data sources, consequently mitigating the latency related to the data transfer to the core, as observed in edge computing [19]. Therefore, FG supports the network load as the advancement of multitier offloading services matters to the network's core. App developers and content providers can utilize the FC systems providing users with services closer to them. Its applications have a significant position in various areas such as transportation, healthcare, energy grid, smart cities, video analytics, and climate change monitoring.  
FC is employed to handle the high-latency challenge in the apps and services not adequately managed within the cloud computing system. FC platforms support different entities to synthesize their storage, network, and other core functions, which extremely offload the network core computing and communicating burden. At the same time, processing data near the data source delivers a better service quality and structural reinforcement for user data privacy and security. Although many aspects are similar to cloud computing, FC still possesses several differentiating features: mobility support, dense geographical distribution, heterogeneity, proximity, numerous node support, and low latency. These promising features support FC to have scalability, a wide geographic distribution, greater business agility, the predominant position of wireless access, and robust capability for time-sensitive data analysis and streaming applications [20].