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Fog computing architecture is composed of highly dispersed heterogeneous devices with the intent of enabling deployment of IoT applications that require storage, computation, and networking resources distributed at different geographical locations [21]. Multiple high-level fog architectures have been proposed in the literature [22–24] that describe a three-layer architecture containing (1) the smart devices and sensor layer which collects data and send it forward to layer two for further processing, (2) the fog layer applies computational resources to analyze the received data and prepares it for the cloud, and (3) the cloud layer, which performs high intensive analysis tasks.

Bonomi et al. [10] present a fog software architecture (see Figure 2.4) consisting of the following key objectives:

 Heterogeneous physical resources. Fog nodes are heterogeneous devices deployed on different components, such as edge routers, access points, and high-end servers. Each component has a different set of characteristics (i.e. RAM and storage) that enables a new set of functionalities. This platform can run on multiple OSes and software applications, deriving a wide range of hardware and software capabilities.

 Fog abstraction layer. The fog abstraction layer consists of multiple generic application programming interfaces (APIs) enabling monitoring and controlling available physical resources like CPU, memory, energy, and network. This layer has the role of making accessible the uniform and programmable interface for seamless resource management and control. Furthermore, using generic APIs, it supports virtualization by monitoring and managing multiple hypervisors and OSes on a single machine with the purpose of improving resource utilization. Using virtualization enables the possibility of having multitenancy by supporting security, privacy, and isolation policies to ensure the isolation of different tenants on the same machine.

 Fog service orchestration layer. The fog service orchestration layer has a distributed functionality and provides dynamic and policy-based management of fog services. This layer has to manage a diverse number of fog nodes capabilities; thus, a set of new technologies and components are introduced to aid this process. One of these components is a software agent called foglet capable of performing the orchestration functionality by analyzing the deployed services on the current fog node and its physical health. Other components are a distributed database that stores policies and resource metadata, a scalable communication bus to send control messages for resource management, and a distributed policy engine that has a single global view and can perform local changes on each fog node.

Figure 2.4 Fog computing architecture [10]. (See color plate section for the color representation of this figure)