Real-time Industrial Networks Research Articles

Delay-Controlled Bidirectional Traffic Setup Scheme to Enhance the Network Coding Opportunity in Real-Time Industrial IoT Networks

Recently, network coding has become a promising transmission approach to support high throughput and low latency in distributed multi-hop networks. In this paper, we develop a delay-controlled distributed route establishment scheme that can provide maximal bidirectional transmission to enhance network coding gain while satisfying a time-critical route setup. The scheme is called network coding-aware delayed store and forwarding (NC-DSF). It delays the received route information packets before forwarding them according to the link status and network topology. We propose a tight delay function derived using a strict end-to-end delay bound for delay control. Subsequently, we suggest a relaxed delay function derived using realistic and practical conditions. Finally, we propose a load-weighted delay function considering the trade-off between bidirectionality and network-load balancing. The simulations confirm that the proposed scheme offers increased throughput and decreased latency in mesh and random multi-hop networks. The proposed transmission scheme, NC-DSF, can be efficiently employed in future industrial internet of things networks requiring a time-constrained route setup, high throughput, and low latency.

Optimal Power Scheduling for Uplink Transmissions in SIC-Based Industrial Wireless Networks With Guaranteed Real-Time Performance

The $k$ -SIC (successive interference cancellation) technology can support at most $k$ parallel transmissions, and thus fast media access can be provided, which is vital for real-time industrial wireless networks. However, it suffers from high power consumption because high interference caused by parallel transmissions has to be overcome. In this paper, given the real-time performance requirements, we consider a network supporting $k$ -SIC, and study how to minimize aggregate power consumptions of user equipments for uplink transmissions by jointly addressing power allocation and user scheduling. We show that the problem is solvable in polynomial time in the case of continuous transmit powers by an algorithm with complexity of $O(n\text{log}(n))$ , where $n$ is the number of user equipments. In the case of discrete transmit powers, the problem is shown to be polynomially solvable for 2-SIC, and we also propose an approximation algorithm for $k$ -SIC where $k>2$ . Experimental evaluations reveal that the real-time performances have tremendous impacts on both the aggregate power consumption and the maximum of the transmit powers of user equipments. Besides, the usability of SIC in low-power applications is also shown by experimental evaluations.

The role of measurement in smart cities pilot projects [Future I&M

Dear readers, I met Stefano at the International Measurement University that took place in Trento, Italy. He was there with some colleagues from Brescia University. His main interests then were smart sensors and measurement in industrial environments. He continued to follow this domain and completed his master’s thesis on real-time Ethernet industrial networks and received his Ph.D. degree in measurement instruments for field level industrial communications. Since then, he has widened his area and decided to embed measurements with sensors and industrial communications reaching Smart Cities. So, we will have to keep in touch to see what boundaries he is going to tear down!

Latency and Traffic Reduction for Process-Level Network in Smart Substation based on High-availability Seamless Redundancy

Process-level communication network brings digital technology to the high-voltage switchyard, a major stage in the evolution to ensure the protection control and data acquisition of smart substation. This network requires a mission-critical protocol such as high-availability seamless redundancy (HSR). Two main drawbacks of HSR, however, are the transmission latency introduced by each hop in the single ring (SR) topology and the unnecessary traffic due to the duplicated copies of sending frames. This study presents two enhanced solutions and fully implements quick removing (QR) approach to HSR for improving the latency and reducing the traffic volume in process-level network. The main idea of these two enhanced solutions is to reduce the minimum number of hops required for delivery messages to destinations for reducing the maximum end-to-end latency (ML). To achieve traffic reduction, the QR approach is concretized in HSR nodes for fully applying to any closed-loop HSR networks. Performance of IEC 61850-based process bus networks are analyzed theoretically and demonstratively by Network Simulator-2 (NS-2) and OPNET Modeler®. The combination of enhanced solutions and the QR algorithm solves both main drawbacks of HSR, improving the network performance optimally. These enhancements of HSR are applicable to not only on substation automation networks, but also to any real-time industrial networks.

Saturated distributed coordination function Markov model for noisy soft‐real‐time industrial wireless networks

The use of wireless technology in industrial networks is becoming more popular due to its numerous advantages. Providing an accurate model to study its performance parameters, is an essential step in designing a reliable and real-time industrial wireless network protocol. Most of the existing models are accurate only for data networks which have large packet payloads and high signal to noise ratio (SNR) characteristics, and cannot be applied to study the performance of industrial networks which have short packet lengths and are used in harsh and noisy environments. In this paper a novel three-dimensional discrete-time Markov chain (DTMC) model has been proposed for the IEEE 802.11-based industrial wireless networks using the distributed coordination function (DCF) as the medium access control (MAC) mechanism. It considers both causes of the backoff freezing: busy channel and the successive inter-frame space (IFS) waiting phase. In this way, it provides a much more accurate estimation of the channel access and collision probabilities, resulting in more accurate network metric calculations. Also, based on the proposed model, a simple and accurate packet delay analysis is provided in the worst-case saturated traffic and error-prone channel condition which in comparison with similar works provides more accurate results.

Network Interactions and Performance of a Multifunction IEC 61850 Process Bus

New substation technology, such as nonconventional instrument transformers, and a need to reduce design and construction costs are driving the adoption of Ethernet-based digital process bus networks for high-voltage substations. Protection and control applications can share a process bus, making more efficient use of the network infrastructure. This paper classifies and defines performance requirements for the protocols used in a process bus on the basis of application. These include Generic Object Oriented Substation Event, Simple Network Management Protocol, and Sampled Values (SVs). A method, based on the Multiple Spanning Tree Protocol (MSTP) and virtual local area networks, is presented that separates management and monitoring traffic from the rest of the process bus. A quantitative investigation of the interaction between various protocols used in a process bus is described. These tests also validate the effectiveness of the MSTP-based traffic segregation method. While this paper focuses on a substation automation network, the results are applicable to other real-time industrial networks that implement multiple protocols. High-volume SV data and time-critical circuit breaker tripping commands do not interact on a full-duplex switched Ethernet network, even under very high network load conditions. This enables an efficient digital network to replace a large number of conventional analog connections between control rooms and high-voltage switchyards.

NDIS-based virtual polling algorithm for IEEE 802.11b for guaranteeing the real-time requirements

This paper focuses on the feasibility of IEEE 802.11b wireless LAN for real-time wireless industrial network. In general, it has been known that IEEE 802.11b is not suitable for industrial networking because its medium access control method is the contention-based CSMA/CA (Carrier Sensing Multiple Access with Collision Avoidance) that exhibits unstable performance under heavy traffic and unbounded delay distribution. As an attempt to circumvent the probabilistic nature of IEEE 802.11b, this paper presents an enhanced four-layer architecture using the Network Driver Interface Specification (NDIS) and a virtual polling algorithm. Also, the enhanced four-layer architecture's performance is compared with that of conventional IEEE 802.11b. Based on the experimental results, it is found that the enhanced four-layer architecture for IEEE 802.11b is a very promising alternative for wireless industrial networking.

다계층 구조를 가진 산업용 스위치드 이더넷에서의 실시간 전송 특성

The real-time industrial network, often referred to as fieldbus, is an important element for intelligent manufacturing systems. Thus, in order to satisfy the real-time requirements of field devices, numerous fieldbus protocols have been announced. But, the application of fieldbus has been limited due to the high cost of hardware and the difficulty in interfacing with multi-vendor products. Therefore, as an alternative to fieldbus, the computer network technology, especially Ethernet (IEEE 802.3), is being adapted to the industrial environment. However, the crucial technical obstacle for Ethernet is its non-deterministic behavior that makes it inadequate for industrial applications where real-time data have to be delivered within a certain time limit. Recently, the development of switched Ethernet shows a very promising prospect for industrial application due to the elimination of uncertainties in the network operation resulting in much improved performance. This paper focuses on the application of the switched Ethernet with cascade structure for industrial communications. More specifically, this paper presents an analytical performance evaluation of switched Ethernet with cascade structure, and a case study about networked control system.

Real-time performance evaluation of urgent aperiodic messages in FF communication and its improvement

In distributed control system (DCS), computation tasks, which usually reside in different nodes and communicate with one another to accomplish a common goal, have to be executed timely. Therefore, there is a need for special-purposed real-time industrial networks. Foundation Fieldbus (FF) is characterized by explicitly distinguishing between periodic and aperiodic messages. Centralized Media Access Control (MAC) is utilized by FF to support periodic messages, and distributed MAC to support aperiodic messages. It is indicated that FF's current mechanism using Pass Token (PT) priority and PT circulation period cannot effectively guarantee the real-time requirement of important aperiodic messages. A detailed analysis shows the method of computing Actual PT Circulation Period (APTCP) should be improved. An improved method of computing APTCP is proposed in this paper, and then a method of determining Setting PT Circulation Period (SPTCP) is presented accordingly. In the end, simulation validates the effect of the improved method on the real-time performance of urgent aperiodic messages in FF.

실시간 산업용 통신을 위한 Switched Ethernet의 성능 평가

The real-time industrial network, often referred to as fieldbus, is an important element for building automated manufacturing systems. Thus, in order to satisfy the real-time requirements of field devices, numerous fieldbus protocols have been announced. But the application of fieldbus has been limited due to the high cost of hardware and the difficulty in interfacing with multi-vendor products. Therefore, as an alternative to fieldbus, the computer network technology, especially Ethernet (IEEE 802.3), is being adapted to the industrial environment. However, the crucial technical obstacle for Ethernet is its non-deterministic behavior that makes it inadequate for industrial applications where real-time data have to be delivered within a certain time limit. Recently, the development of switched Ethernet shows a very promising prospect for industrial application due to the elimination of uncertainties in the network operation resulting in much improved performance. This paper focuses on the application of the switched Ethernet for industrial communications. More specifically, this paper presents an analytical and experimental performance evaluation of the switched Ethernet and a case study about networked control system.

Performance evaluation of switched Ethernet for real-time industrial communications

The real-time industrial network, often referred to as fieldbus, is an important element for building automated manufacturing systems. Thus, in order to satisfy the real-time requirements of field devices such as sensors, actuators, and controllers, numerous standard organizations and vendors have developed various fieldbus protocols. As a result, the IEC 61158 standard, including Profibus, WorldFIP, and Foundation Fieldbus, was recently announced as an international standard. These fieldbus protocols have an important advantage over the widely used Ethernet (IEEE 802.3) in terms of the deterministic characteristics. However, the application of fieldbus has been limited due to the high cost of hardware and the difficulty in interfacing with multivendor products. In order to solve these problems, the computer network technology, especially Ethernet, is being adopted by the industrial automation field. The key technical obstacle for Ethernet for industrial applications is that its nondeterministic behavior makes it inadequate for real-time applications, where the frames containing real-time information, such as control command and alarm signal, have to be delivered within a certain time limit. Recently, the development of switched Ethernet shows a very promising prospect for industrial applications due to the elimination of uncertainties in the network operation that leads to the dramatically improved performance. This paper focuses on the application of the switched Ethernet for industrial communications. More specifically, this paper presents the performance evaluation of the switched Ethernet on an experimental network testbed along with an implementation method for using the switched Ethernet for industrial automation.

Industrial Multimedia over Factory-Floor information Networks

In this paper we describe a real-time industrial communication network able to support both control-related and multimedia traffic. The industrial communication network is based on the PROFIBUS standard, with multimedia capabilities. The TCP/IP suite of protocols, properly integrated within the PROFIBUS communication stack, supports these capabilities. From the timeliness point of view the challenge is two folded. On one hand the multimedia traffic should not interfere with the timing requirements of the ‘‘native‘’ control-related PROFIBUS traffic (typically hard real-time). On the other hand multimedia traffic requires certain levels of quality-of-service to be attained. Copyright © 2001 IFAC