# Analysis of Security Issues and Countermeasures for the Industrial Internet of Things
## 2 IIoT Architecture  
There is no single and well-accepted IIoT architecture at present. We consider an IIoT architecture to be dependent on the system's requirements and the designer's choice. We observe that a single vendor does not propose an ideal IIoT architecture. Therefore, using standards can help the architecture take advantage of evolving technologies and standards. Consequently, it can use powerful IIoT devices when they become available. Different vendors support standards such as WirelessHART [41] and Foundation Fieldbus [42]. The advantage of using standards is that if a particular type of sensor from one vendor fails, it is possible to replace it with another vendor as long as they use the same protocol standard and network technology. This is the crucial part of interoperability. When a sensor is changed, typically, the system does not need to replace the other sensors or the higher levels of the IIoT architecture. This signifies the use of standard protocols and networks for the IIoT systems. On the other hand, new standards have begun to emerge due to the need to monitor industrial systems and processes, for example, new industrial wireless sensor network (IWSN) standards of ZigBee, WirelessHART, ISA 100.11a wireless, and Wireless network for Industrial Automation-Process Automation (WIA-PA), to name a few [43]. Before going to a detailed discussion of security issues and their potential countermeasures, in this section, we discuss the foundation of a basic IIoT architecture within which these security issues would function. Several proposals present various architectures for IIoT. Mostly, these architectures are classified based on layers. Significantly, these layers typically overlap with IoT architecture. However, significant differences are from the business, usage, functional, scalability, and implementation points of view. Next, we discuss some basic architectures of an IoT system and then see how these architectures can be integrated into the IIoT space. A three-layer IoT architecture is discussed in [44]. The layers are perception (sensing information from the physical layer), network (provides communication between the layers), and application layers (facilitates communication between the end-users via different apps). To provide more granularity in the system, [45] proposes a four-layer IoT architecture. These layers are sensing, network, service, and application interface. The sensing layer is responsible for the collection of data sensing from the physical environment. The network layer helps in communications among the various components with the architecture, supports data aggregation, and maintains Quality of Service (QoS). The major functionalities of the service layer are service processing, divisions, monitoring, and configuration. Finally, the top layer (i.e., the application interface layer) is responsible to provide smart IoT services to the end-users. Proposals [46; 47; 48] present a five-layer IoT architecture. These layers are object, object abstraction, networking, service composition, and application. The object layer (also known as the perception layer) is the bottom layer of the architecture. It is composed of vast and heterogeneous sensors, actuators, and other smart-sensing objects. The object abstraction layer passes the collected data to the next layer, called the networking layer. It is responsible for providing networking between the other layers of the architecture. The service management layer performs the service decisions tasks. The service composition layer helps to aggregate various services using specific hardware platforms. Finally, the application layer renders desired interfaces for the end-users to access the services via apps. [PERSON] et al. [49] present another five-layer architecture for the IoT. These layers are perception, access gateway, network, middleware, and application layers.