# Recent Advances in Evolving Computing Paradigms: Cloud, Edge, and Fog Technologies
## 3 Evolving Computing Paradigms and Related Concepts
### Fog Computing
#### 3.12.2 Architecture  
The illustration of the fog architectural model has recently been a prominent area of research. Extensive related research alluded to the architecture comprising of three-layer [15; 17; 107; 108; 109]. Moreover, the N-Tier architecture recommended by the OpenFog Consortium may be regarded as an enhancement of this three-layer model [10]. 1. Three-Layer Architecture  
IoT Layer  
It is nearest to the end-user's physical setting. Sensors, smart cars, drones, smartphones, tablets, and other devices compose this layer. Even though some of these devices possess computational capabilities, they are used as mere smart sensing devices at this layer. Overall, these devices are widely distributed geographically to sense and transfer data to the next higher layer for the sake of storage and computation. The centralized cloud infrastructure composes the majority of this tier. It comprises several servers with advanced computational and storage capabilities offering a variety of services. Dissimilar to typical cloud computing architectures, the fog model can ease the burden on cloud resources by efficiently transferring computational services from the cloud layer to fog and enhancing productivity. Figure 8: Typical cloud–fog computing architecture. The OpenFog Consortium's recommended N-tier architecture [10] is rendered in Figure 9. Its primary intent is to offer a standard guideline for implementing fog computing in a given circumstance. Though fog systems are deployed in a scenario-specific manner, the core elements of the architecture are apparent to every fog deployment. Endpoints (or things), fog nodes, and the cloud are the three main components of the idea. In addition, multiple layers of fog nodes (N-tiers) may constitute the fog layer; when the nodes are more distant from the end devices, improving computing potential and intelligence are acquired. The higher levels of the fog layer refine and collect more pertinent data; therefore, enhancing intelligence. The scenario-specific needs ascertain the number of tiers in a particular implementation. Furthermore, fog nodes connected in a mesh on each layer are adept at providing added characteristics such as fault tolerance, elasticity, load balancing, etc. Thus, the fog nodes may interact both vertically and horizontally. Fog nodes may be categorized based on their closeness to the cloud and endpoints:  
* Lowest tier: with the primary focus on the acquisition, normalization, and collection of data obtained at the sensors, and the actuators are managed by fog nodes. * Intermediate tier: filtering, compressing, and altering data received from the bottom layer is the responsibility of fog nodes in the intermediate tier; on average, these nodes are better at analyzing data. * Highest tier: aggregating data and eliciting knowledge from it is the intent of fog nodes at this tier. * Seven-Layer Architecture  
A fog computing model positioned between the cloud layer, and edge devices extend services of processing, network, and storage to IoT devices, with the primary intent of minimizing latency for time-critical applications. The services offered by the fog model  
Figure 9: N-tier architecture. are limited compared to the sophisticated cloud data centers. In line with various fog architectures presented by researchers [110; 111] with diverse layers, a reference architecture comprising distinct layers with designated tasks is featured here and depicted in Figure 10.  
* Physical layer  
The sensors are the devices that serve as the primary data source producing diverse data in a fog setting. The data may be from smart devices and homes, autonomous vehicles, closed-circuit television (CCTV) monitoring, traffic systems, sensors tracking temperature and humidity, etc. Alongside physical sensors, the physical layer also comprises virtual sensors, which also produce data as well. * Fog device, server, and gateway layer  
An individual device or IoT could be a fog device, server, or gateway.