Networks and Real-Time Traffic for Industrial Control Applications - Essay Example

Networks and Real-Time Traffic for Industrial Control Applications Abstract Pervasive adoption of location tracking technologies, such as GPS, that heavily rely on internetworks of computers, internet, and communications technologies has realized growing interest in the last few years. This technologies use real time data, sending and receiving information on the go. The infrastructure required for processing large volumes of the sensor data passed in real time to derive useful information is growing and calling for flexibility in terms of being mobile and reducing the installation hustles. Wireless infrastructure has come into the picture and provided solutions to the installation and positioning of this gadgets that handle data. The question is whether the solution, wireless, has enough capacity to support this systems. Wireless technology surveyed seeks to establish the capacity, reliability and most importantly the future and existing modifications to cater for industrial control application needs for data, voice and video transfer. An in depth analysis of the existing technology and the current support for real-time traffic in industrial control applications has been reviewed. Real-time traffic flows in a network and is required within specific time restraints of a process or simultaneously supply information to another system it is assisting (Rowe et al. 2006). Usually the traffic flow must be faster and arrive slightly earlier than needed by the receiving device. This is to facilitate appropriate intervention of the data supply. The real-time traffic flow is supported by real-time systems that must operate in a synchronized way and within the same time constraints. The real-time traffic flow towards a receiving device is usually data (inputs) from sensors purposely to compute and monitor system control parameters –outputs- needed for the correct system or process operation on the receiving device. The type of control and monitoring functions provided by the receiving device ranges over a wide variety of tasks, such as turn-off and turn-on signals to switches; feedback signals sent to controllers to provide adjustments or corrections (Simacek 2002, p. 56). Real-time traffic requirements put emphasis on availability and as such data is required timely to keep up with the person operating the control application. The control application may be a computer terminal or some other device of similar nature and has a keyboard and screen to assist the operator of the system. The terminal device in this case supports the operator or operators and provides retrieval, access and storage functions through a database management system as well as computational power and data processing. A ‘Global Village’ this is a common phrase from the Information Technology experts who infer that the world has become reachable more than it ever has been. Predominantly this has been made possible by the availability of real-time information, as it happens, making an individual all round and knowing all that is taking place. Within seconds of an event happening it spreads all over the world in a matter of seconds and reaches the global audience. It is extremely valuable to commercial organizations, such as, commercial fleet operators, agencies etc. to obtain real-time traffic information from their monitoring systems. Besides, making their operation smooth it provides immense benefits to make predictions of operations and create scenarios for their business strategies. Network operations that support real-time traffic have fundamental importance and are designed with the critical nature of business processing in mind. Real-time traffic over the wireless standards, IEE 802.11, is slowly catching up and becoming popular. There are a myriad of streaming services that are coming up every day, for example, videoconferencing and video on phone. Data is currently a dominant service in wired network but “special service” in wireless network infrastructures. However, real-time streaming is dominant in the wireless environment markets. The need to provide real-time data service by wireless network infrastructure is a critical issue in design and deployment of wireless networks (Murthy and Manoj 2004, p. 148). Wireless Networks are intended to provide as many features and advantages of traditional wired LAN technologies, for example Ethernet but wirelessly. They work without cable limitations and radio frequencies (RF) or use infrared light (IR as transmission medium. Transmissions are based on two improvements of a spread spectrum method, both standardized by the Institute of Electrical and Electronics Engineering 802.11b and used in Bluetooth and WLAN (Karl and Willing 2007). The first method is Direct Sequence Spread Spectrum and supports data rates of up to 11Mbps. The second method is (FFHS) Fast Frequency Hopping Spectrum with data rates of up to 2 Mbps. Advantages of wireless include mobility, cost saving, flexibility, installation in areas that wire cannot go through and reducing overall installation time. Bluetooth technology is also a WLAN standard and uses the 2.4 GHZ frequency; this is the only unlicensed frequency in most of countries. The short-range radio technology, Bluetooth, aimed at simplifying data communications among devices. The telecom market, however, has extensively used the Bluetooth transmission capabilities. Industry applications implementing Bluetooth in real-time traffic control systems are still under investigation. It was not initially designed and developed for real-time traffic control especially in industrial application; it was tailor-made for common data and voice transmissions, cable replacement purposes, ad hoc networks and this is a hurdle since industrial applications are different. A critical issue in design and implementation of wireless networks is the provision of real-time data service. Distributed Queuing Request Update Multiple Access is already proposed as a demand assignment (MAC) medium access control protocol to facilitate efficient medium sharing by multiple mobile users. With the assistance of a transmission policy, DQRUMA has the potential to provide real-time quality of service for time-constrained data traffic on a network. The DQRUMA is an algorithm that can control packet transmission in packet-switched wireless networks efficiently and support real-time service in real networks (Gohdrat 2002). WiMAX is another wireless access network and is a technology with a lot of promise for the future of broadband services. This is due to the capacity it to provide various communication services in various application environments and simultaneously guarantee (QOS) quality of service. In theory wireless data networks have two types of system structures. One is the ad hoc network, where every device works in a peer-to-peer fashion and the other is the centralized network with a base station to centrally control the entire network. The wireless infrastructure interface consists of the wireless data link control layer and physical layer, which contain logical link control sub layers and a medium access control. Medium access control protocols are needed to schedule packet transmission over the limited wireless channels. An MAC design in a network is highly expected to make efficient use of the limited resources and satisfy the constraints on the transmitted packets. The collision-free media access control protocols brought forward for the centralized structure of the wireless network can be separated into two categories: reservation-based techniques and polling-based techniques. Bianchi( 2000, pp. 50-51) posits that reservation-based protocols transmit access request to inform the base station of the required constraints and timeslots on the transmission by considering the transmission channel or another and assigns timeslots on the channels to individual mobile nodes, based on the channel access requests for them. Polling- based transmissions assign transmission rights to different by polling each node in the network ahead of transmission. Table 1: Comparing the Different Wireless LAN Technologies Approaches used n streaming data over wireless networks are IP networking towards wireless and mobile environments. The streaming requires high quality of service to guarantee clear and good reception of the signal as its broadcasted. Real-time traffic is not sensitive to delay but very sensitive to jitter. Voice over IP and Video over IP are classical examples of real-time data streaming and effect of lost packets is strongly dependent on coding and decoding. On one hand, the narrow bandwidth available in wireless networks poses some bottlenecks in the effective wireless streaming of the real-time data. For instance, the 802.11a standard stream data at 54 Mbps, 802.11b standard stream data at 11Mbps while the wired standard 802.3ae stream data at 10Gbps. This is basically 900 times faster. The high control overheads that are caused by large synchronization fields and more packet management in access point registrations are the root of the problem. Additionally wireless infrastructure has inherent contention media from the issue of open space transmission. Industrial process control involved applying technology to operations that alter raw material into desired products (Agrawal 2010, p. 67). Virtually everything we consume undergoes some type of automatic or monitored process control during its production. In manufacturing environments, processes control provides better product consistency and higher productivity while at the same time reducing production costs. Process control in these industrial applications relies on gathering input information, initiating action and evaluating the information. Monitoring field devices whose outputs are of a bi state is one of the main activities of these control applications. Looking at a real scenario; manufacturing plant. Items are put in boxes and sent down a conveyer belt to the loading bays waiting with delivery trucks. Each delivery truck can hold 200 boxes. As the boxes get to the loading bay, workers load them in the first truck and when full the remaining boxes must be directed to the second truck. The diversion allows the first truck to move out of position and leave room for the second truck. In the event that an emergency problem arises there must be some way to stop the conveyor. This scenario described allows us to look more insightfully into the industrial process control and how automation of the process relies on real-time traffic. In a broader sense it allows us to peer into how real-time traffic is passed on and specifically focus on wireless network as the means of passing on this traffic. An industrial control system in general encompasses different types of control systems in use in industrial production. These systems could be supervisory control and data acquisition (SCADA) and distributed control systems (DCS) or other embedded control system configurations often found in industrial sectors and in critical infrastructures. They ICS systems may operate under very little or no supervision at all and largely may be interaction between two systems that are autonomous or a system and its subsystem. ICS systems as traditionally used in industries such water, oil, electrical, data and gas. Operator-driven or automated supervisory commands can be directed to remote station control devices based on signal information received from the main stations and vice versa. The remote stations on the field control local operations and predominantly collect data from sensor systems. Additionally they monitor the local environs for any alarm conditions. The ICS systems have their ground and functional operation heavily relying on real-time systems which provide real-time traffic flow and analysis of the information that is incoming. Currently on the internet there are different types of applications that run on the network and have diverse statistical characteristics and quality of service requirements. Time critical and operation critical data has been classified to underscore the privileged nature of information (Anderson 2002). The available data is expressly required to have high accuracy with acceptable memory and computational overheads. Performance of the real-time traffic should be reliable, available and in expert analysis meet the network performance indices. These characteristics have to do with the quality of service and guarantee of data delivery. Traffic on a network is heterogeneous; this means that it consists of a variety of types of messages that represent assorted information media and the constituent parts. In this perspective it can be viewed as a burst of information flowing from uncompressed, continuous fixed-rate source streams to very short uncoordinated bursts of information. The receiving client and sending server should have minimum requirements in terms of design. For instance, a synchronization clock should be in place to have the two running on the same time slots, and the hardware compatibility issues should be well handled to facilitate prompt response to requests. By the design, the client has to specify and request specific information plus characteristics and requirements of expected input traffic to minimize efforts spent on sorting and muddling through the real time information as it flows in. Wireless networks are inherently unreliable from the medium they use in transmissions. The reflection, crucial interference with other devices using the same frequency and multiple path effects are some of the challenges in wireless networks. Power feeds to the wireless devices also poses a problem since the power supply lines cannot be installed everywhere. A pure battery solution is viable in response to the power supply problem, however, it may not be very attractive since the advantage of the wireless dies soon the battery replacement is necessary. In terms of power supply challenge, special attention needs to be applied in individual cases. Deterministic data transfer with Bluetooth is difficult since it has an ARQ scheme (not in voice packets). Suitability and usability of WLAN (802.11b specification) for industrial purposes and its contrast and comparison to Bluetooth technology is under research by many companies. Like Bluetooth, WLAN original design was not for industrial applications and suffers from similar defections. New standards implementation such as 802.11g and 802.11a can greatly enhance WLAN usability in real-time traffic control applications. The new standards introduce faster transmission but they do not add more reliability. Design of a predictive controller dealing with varying delays or control algorithms is an issue that might improve suitability of WLAN for industrial applications. It deals with varying delays or control algorithms that handle packet timeout or missing data. The original use that Bluetooth was designed for is mobile phones. It is however a recent invention that came to support data communication on mobile devices with a wireless capability. It is a challenge in industrial environment since the demands for real-time traffic are different. The combination of devices used and complexity of required tasks to provide specific measurements is not possible to accomplish due to technological problems related to bridging and routing packets between Access point with Bluetooth. Conclusion In open wireless standards for industrial process control meeting the strict real-time requirements of process control requires many challenging features in a technology. The overall architecture design should be focused on wireless technology to support large bandwidth requirements and 100 percentage reliability and availability. However, in the design, implementing specifications such as timer design, security and synchronization of the communication systems requires a lot of technical expertise and sometimes applies to individual situations. Novel ways to handle the challenges posed by wireless network standards in industrial control applications support are under prototyping. For instance, new hardware accelerator packages and also new protocols and standards from the Institute of Electrical and Electronic Engineering. Coexistence of WLAN, Bluetooth technologies in one environment is something to watch out for. It is not possible to scrap these existing technologies since they do not support industrial applications requirements for real-time traffic and therefore working with them is more fruitful and could lead to new innovations. References Anderson, M 2002, ‘Bluetooth for industry control applications’, The Industrial Ethernet Book, Vol. 3, no.11, pp. 5-11. Agrawal, D, P & Zeng, Q 2010, Introduction to wireless and mobile systems, CL-Engineering, Delmer. Balakrishnan,H et al. 2004, ‘The distance-2 matching problem and its relationship to the mac-layer capacity of ad hoc wireless networks’ , IEEE Journal on Selected Areas in Communication, pp. 56-57. Bianchi, G 2000, ‘Performance analysis of the IEEE 802.11 distributed coordination function’, IEEE Journal in Selected Areas: Communication, pp. 50-51. Dias, F, Berry, F, Serot, J & Marmoiton, F 2007, ‘Hardware, Design and Implementation Issues on an Fpga-Based Smart Camera’, International Conference on Distributed Smart Cameras (ICDSC). 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