You are presented with multiple paper abstracts, alongside the associated literature review and chapter titles. Given the provided information, you are going to do a literature review. Please generate a coherent literature review that synthesizes the content, draws connections between different works, highlights major findings, and identifies any gaps in the existing research.

Literature Review Title: A Survey on Industrial Internet of Things: A Cyber-Physical Systems Perspective 
Chapter Title:  2) OTHER INTEGRATIONS 
1. Abstract of Cited Paper (BIB001):  In this paper, a scheme for closed loop speed control of DC motor in four quadrants using Programmable Logic Controller (PLC) is discussed. The armature voltage is varied using a Class E chopper circuit. The individual switches in the chopper circuit are switched using Pulse Width Modulation (PWM) control signals generated by PLC. Duty cycle of PWM signals are varied by PID controller of the PLC. Three main modes of operation have been implemented: Speed control mode, sinusoidal input tracking mode and step input tracking mode. The resulting current, voltage and speed waveforms are recorded on Digital Storage Oscilloscope(DSO) and analyzed. Speed, set point and control variables are observed on GUI made using SCADA software.

Literature Review:
PLCs are often used as control components in SCADA and DCS systems to provide process control. In this case, similar to RTUs, the PLC plays the role of interconnection between control center and end-devices (e.g., sensors and actuators). As an example of integrating SCADA and PLC, Singh et al. BIB002 leveraged SCADA and PLC to conduct monitoring and control of DC motor speed. The PLC mainly generates control signals to adjust motor speed and the SCADA provides remote monitoring. In addition, Endi et al. BIB001 proposed a three-layer PLC/SCADA architecture, which consists of supervisory control layer, process control layer, and field instrumentation control layer. The three-layer architecture leverages open system technology (e.g., open standards protocol) to enable seamless communication between different layers, such that the scalability, compatibility and performance of remote control and monitoring can be improved.