# A Study on the Design of Fog Computing Architecture Using Sensor Networks
## 2 Related Research
### Sensor Network  
Due to the development and commercialization of wireless communication technology, sensor network technology has attracted great attention. A sensor network is the environment to connect  
Figure 3: The Structure of Fog Computing. hundreds of devices. Therefore, wireless sensor network-based products which allow configuring a sensor network environment, have a large market [13]. Figure 4 shows structure of a sensor network in the IoT environment. Under the sensor network environment, devices are distributed at various areas and form a network, making it impossible to collect devices, replace hardware and replace or charge a battery. Under a sensor network environment, research and development of network and protocol technology have been conducted to improve energy efficiency, considering the hardware limitations of devices. A variety of conditions including hardware limitations, network topology, the communication environment and power consumption must be considered to construct the sensor network environment. In general, sensor devices in a sensor network adopting a cluster-based protocol transmit measured data to the m-proxy, which is a small unit proxy server of fog computing. The m-proxy server is a device that collects data from the network in the cluster structure and transfers it to the proxy server in fog computing. The proxy server is a system that collects sensing information sensed by a sensor device, or links event data to the outside of the sensor network and manages the related sensor network. Due to the development of technology, recent sensor device are becoming low cost, low power, and miniaturized. However, they have also some technical difficulties such as replacement of hardware and replacement or charge of battery. Studies on the development of technology to overcome such shortcomings are currently undergoing. Considering the fact that it requires data aggregation to reduce waste of energy caused by duplicate delivery of information between near devices in a sensor network, clustering-based hierarchical management has many advantages. In other words, fog computing creates a local cluster, transfers similar information about events happening at a near area to the m-proxy server, realizes energy effective routing by allowing the m-proxy server to perform data aggregation, and prevents flooding of ineffective inquiries by transferring requested inquiries through the m-proxy server. A sensor network in IoT environment adopting clustering algorithm is divided into smaller areas called a cluster, as shown in Figure 5. A cluster has an m-proxy server. An m-proxy server collects data from cluster members and forwards the collected data to a proxy server. Figure 4: Sensor Network Configuration in the IoT environment. One of the most layered routing protocols used in sensor networks is the Low Energy Adaptive Clustering Hierarchy (LEACH) protocol. LEACH is a method to periodically replace m-proxy servers with the highest energy consumption based on probabilities. It prolongs the lifetime of the sensor network compared to existing routing protocols. However, a certain number of m-proxy servers are not selected for each round by a probabilistic m-proxy server determination method and the m-proxy servers can be concentrated in a specific area in the sensing field. To solve this problem, a LEACH-Centralized (LEACH-C) routing protocol that complements LEACH has been proposed, but LEACH-C also requires additional energy consumption for all devices to communicate with the proxy server in every round, so additional overhead occurs. In addition, the data transmission process between the proxy server and the sensor devices is the same as the clustering-based routing technique. However, in this technique, in selecting the m-proxy server differently from LEACH, the m-proxy server is selected according to the position information of the devices and the energy holding amount.