Compare and Contrast Essay on SCADA and DCS systems

DCS stands for (Distributed Control Systems) and SCADA represents (Site Control And Data Acquisition) systems. While SCADA comprises Data Acquisition as can be observed from its name, DCS conversely stands only for control (Nabil, Bourennane & Benmohammed, 2016). The reason behind this difference in components is that in the past, computer networks were either nonexistent or were accompanied by inconveniently low bandwidth. In this environment, a SCADA system was used for controlling the top-level for a substantial number of lower-level intelligent agents (Colombo, Karnouskos & Bangemann, 2014). It was neither cost effective nor practical to use a single system to regulate all the little details of a system. Subsequently, in the prevailing circumstances, a substantial amount of the workload involving minute details was handled by DCS devices that simply conveyed information to and received high-level orders from the SCADA system. In the present day, computer systems have made significant advancement is speed and it does not make sense any more to separate SCADA and DCS (Nabil, Bourennane & Benmohammed, 2016). Subsequently, SCADA and DCS have been integrated into a single monitoring and control system. Some areas however favor SCADA while others favor DCS depending on their interests. SCADA and DCS systems are both used to monitor processes, measure important process values and sound an alert when irregularities occur. The two can be used in petrol engineering systems, and power generating installations such as nuclear power stations.

Advantages of SCADA systems

The SCADA systems provide data is utilized in maintenance and operations. The system automates processes reducing the need for many employees to perform tasks therefore cutting costs and boosting productivity. In addition, the system is flexible enough to allow the users to access the maintenance and operation data even when they are not within the premises (Colombo, Karnouskos & Bangemann, 2014). SCADA systems can be connected to asset management systems procurement systems and make allowance for billing systems operation management systems during the course of the HMI and the data historian. SCADA systems are an integral aspect of major sustainability projects. SCADA has been associated with increased process efficiency and reduced maintenance costs.

Disadvantages of SCADA systems

One drawback of SCAD is its poor security that makes it vulnerable to external interference from threats such as hackers.

Advantages of DCS

DCS are different from programmable logic controllers because the former uses a suite of configuration tools that enable integration of the functions of database, control logic, graphics and system security. There is distribution of control applications to system controls that facilitates dedication to particular processes using field devices (Colombo, Karnouskos & Bangemann, 2014). Subsequently, the ability to create and spread control logic across the system controllers allows for the ability to upgrade or modify by inclusion of new controllers or field devices in an effective and precise manner that accelerates updates and incorporation of new equipment. A redundant communications network is used to link the controllers and related inputs/outputs and engineering stations. This facilitates easier data monitoring using the user friendly displays, data logging, alarming and control. It is possible to gather real world data in real time due to the ability to connect filed devices such as actuators and sensors straight linked to input/output modules that relay information between them and assigned controllers. The DCS are also scalable meaning that they can be modified to suit the size of the plant (Colombo, Karnouskos & Bangemann, 2014). The DCS has room for further improvement since new controllers or input and output can be included in future and are automatically updated by the controlling database.

MODBUS and PROFIBUS

Introduction to Modbus

Modbus is the pioneer technology of industrial communication protocols. Modbus was initially created in the mid-1970s by Modicon as a means to connect smart devices with PLCs utilizing a simple master/slave concept (Hong, Cunbo, Chunlei & Lihong, 2014). One of the key features that make it superior in terms of strength is its simplicity. Modbus is simple to execute and not complicated to use. In its early days after its introduction it functioned as a proprietary protocol that could only be used by Modicon. The creators however later published it royalty free making it available for anyone to use. Modicon finally made it an open protocol. Many companies now use it and have modified it to suit their needs resulting in a number of variations that have emerged.

Introduction to ProfibusWhile Modbus is the pioneer of protocols, Profibus is a young protege characterized by its lean and fast nature. Developed in the 1990s, Profibus was made with a view to satisfying all industrial communication requirements for both factory and process automation (Raju & Chandrashekhar, 2014). The protocol has several associated terms that relate to its structure and function such as Profibus DP, Profibus PA, Profisafe, Profidrive, and Profinet (Hong et al., 2014). Profinet was created to utilize the availability of Ethernet and allow simpler inclusion of higher-end Profibus utilities such as Profisafe. Profibus main physical layers are highly detailed and provide excellent noise immunity. Profibus has both standardized outputs and function, block design that not only make it easy to setup and integrate field instruments but also install and use multi-vendor applications.

TCP/IP and OSI layers

OSI(Open System Interconnection)

OSI is a universal standard made up of seven layers that is free of protocols and acts as a communication channel between a user and the network they operate in. in the OSI model, the delivery of packets is guaranteed by the transport layer (Rayes & Salam, 2017). OSI works in a vertical approach. There is a presentation layer and session layer that are kept separately in the OSI model. OSI can be considered as a guidance tool that provides a reference for which networks are built around. Through its network layer, the OSI model avails both connection oriented and connectionless service. However, the OSI model is not well functional when it comes to introduction of protocols into the model due to its inflexibility. OSI compensates for this flaw by making it easy to hide protocols within it and modify them when required (Rayes & Salam, 2017). The OSI model has clear distinction of services, interfaces and protocols.

TCP/IP (Transmission Control Protocol / Internet Protocol)

TCP/IP unlike OSI is made up of 4 layers and is rooted in standard protocols around which the Internet has established. TCP/IP is a communication protocol and enables connection of hosts over a network. In a manner of reasoning, TCP/IP is an implementation of the OSI model (Rayes & Salam, 2017). Unlike the OSI model, delivery of packets is not guaranteed by the transport layer. However, TCP/IP is still more reliable than the OSI model despite this difference. Unlike the OSI model, TCP/IP follows a horizontal approach. TCP/IP has a network layer similar to OSI model but it only provides connectionless service. TCP/IP does not suit any protocol and replacing its protocols is a complicated affair (Rayes & Salam, 2017). There is no distinction of services, interfaces and protocols in TCP/IP. TCP/IP is protocol dependent unlike the OSI model.

CSMA/CD and CSMA/CA

Carrier Sense Multiple Access or CSMA is a Media Access Control (MAC) protocol employed to regulate data flow in transmission of media to prevent loss of packets and ensure the integrity of data (Chakraborty, Islam, Azad & Rahaman, 2016). CSMA has been modified into the CSMA CD (Collision Detection) and CSMA CA (Collision Avoidance). When two transmitters send data simultaneously, a collision occurs. CSMA works by detecting the condition of the medium and prevents or recovers from a collision (Kwon, Seo, Kim & Lee, 2009). Collisions scramble data making it impossible for receivers to distinguish it and causing loss of information. The lost information has to be sent again for the receiver to get it.

CSMA CD works by detecting the incidence of a collision and cutting transmission to prevent wastage of time as the transmitter keeps transmitting (Kwon et al., 2009). CSMA CA on the other hand checks if the medium is in use and if it is busy, CSMA CA ensures the transmitter waits until the medium is idle before sending data (Chakraborty et al., 2016). In this way, CSMA CA reduces the probability of collisions taking place therefore increasing efficiency of the process. CSMA CA minimizes the possibility of a collision while CSMA CD accelerates the time for recovery after a collision (Chakraborty et al., 2016). Typically, CSMA CD is primarily utilized in wired networks while CSMA CA is employed in wireless networks because unlike in wired installations, in wireless installations, transmitters cannot establish if a collision has ensued or not.

References

Chakraborty, D., Islam, M. I., Azad, A. K., & Rahaman, A. S. M. M. (2016). Performance

Analysis of CSMA/CA Network using Modified State Transition Chain. International Journal of Computer Science and Information Security, 14(12), 1064.Colombo, A. W., Karnouskos, S., & Bangemann, T. (2014). Towards the next generation of

industrial cyber-physical systems. In Industrial cloud-based cyber-physical systems (pp. 1-22). Springer International Publishing.Hong, J., Cunbo, J., Chunlei, X., & Lihong, C. (2014). Fieldbus Control System Protocols

Controller Mixing WSN. Computer Measurement & Control, 3, 033.Kwon, H., Seo, H., Kim, S., & Lee, B. G. (2009). Generalized CSMA/CA for OFDMA systems:

protocol design, throughput analysis, and implementation issues. IEEE Transactions on Wireless Communications, 8(8).Nabil, S., Bourennane, E. B., & Benmohammed, M. (2016). Cyber security for wireless semantic

(SCADA/DCS) systems. International Journal of Systems, Control and Communications, 7(4), 307-320.

Rayes, A., & Salam, S. (2017). The Internet in IoTOSI, TCP/IP, IPv4, IPv6 and Internet

Routing. In Internet of Things From Hype to Reality (pp. 35-56). Springer International Publishing.Raju, N. B., & Chandrashekhar, G. (2014). U.S. Patent Application No. 14/231,702.