Jacek Stój

The Cost of Redundancy in Distributed Real-Time Systems in Steady State

The paper presents considerations that refer to introducing the term “cost of redundancy”, and indicates general assumptions that allow defining this term and its quantitative determination. However, “the cost of redundancy” does not apply in this case to financial expenses but only time loses (temporal cost) associated with the use of redundancy in industrial real-time distributed systems. Several computer systems architectures are analyzed from the point of view of that temporal redundancy cost.

Virtualization as a Way to Distribute PC-Based Functionalities

Virtualization theory is well known and successfully used in the computer domain. Personal computer (PC) workstations, as well as their virtual counterparts, are popular for general purposes. PC stations are also popular in networked control systems (NCSs). They are used as system components to deliver user interfaces and to run many important services of the data processing, communication, and database type. In this paper, the usage of virtual PC machines (VMs) is considered in the context of interoperability with NCS. This specific application area requests answers whether virtualization is applicable and secure, and what are the expectations from the temporal characteristics of running services.

Real-Time Communication Network Concept Based on Frequency Division Multiplexing

In all real-time systems the temporal determinism is a crucial aspect. It especially refers to communication networks where real-time communication protocols have to be used. In this area three main methods for achieving temporal determinism may be distinguished: token passing, master-slave and producer-distributor-consumer. All are based on Time Division Multiplexing TDM as a method for gaining the communication bus access. The paper presents a concept of a new communication network where the communication is based on Frequency Division Multiplexing FDM possibly making the data exchange more efficient than in most present solutions.

Influence of Electromagnetic Disturbances on Multi-network Interface Node

The main idea presented in the paper focuses on testing behavior of multi-network interface node while electromagnetic disturbances in transmission line occur. Such node is able to unload an increased traffic in network or provide the security of transmission, especially in cases of temporary overloads, system failure – damage of transmission system, or events occurring in industry area. The authors marked the potential possibilities of using equipment for EMC (Electromagnetic Compatibility) measurements in the process of testing and simulating the real threats (disturbances) that may appear in the object. The final results point out the correct work of developed query distributor system and the opportunities of automatic adjustment of the network topology in case of electromagnetic disturbances.

Network Integration on the Control Level

In the following paper the authors analyze the problem of the network integration on the lowest level of industrial computer system which is the control level. Exchange of information between different levels in integrated pyramid of enterprise process is fundamental with regard to an efficient enterprise operation. Communication and data exchange between levels for different systems are not always the same because of a variability of the used network protocols, communication mediums, system response times, etc. That makes the problem of network integration an important aspect for research.

Temporal Costs of Computing Unit Redundancy in Steady and Transient State

Industrial real-time computer systems are designed to operate with high reliability level. It is most often achieved by the use of redundancy. Additional elements introduced to the system are supposed to make it invulnerable to failures of their redundant components. Implementation of redundancy entails significant extra costs. The financial costs are quite obvious and easy to estimate they are associated with the need to deliver, configure, program, service and maintain additional devices and communication interfaces. There are however another costs which are not so evident because they derive from the system operation and data processing. Those are the temporal costs of redundancy that influence the real-time systems characteristics and in the end may determine the system usability.

Genius Network Communication Process Registration and Analysis

The estimation of the information exchange cycle duration in industrial networks is an essential issue, because the knowledge of this parameter allows answering several questions related to satisfying of assumptions of the real-time system or the redundant systems design. The characteristic features of systems with communication link redundancy are the delays in switching the redundant buses. This may require a registration of the time values, preferably in “on-line” mode. The authors discussed this very issue, trying to achieve the objective of registration of the communication process and the value of network sweep time in an exemplary Genius network, using standard computer tools.

Cost Effective Computing Unit Redundancy in Networked Control Systems Using Real-Time Ethernet Protocol

Designers of distributed computer systems have to take into account many requirements concerning the system operation and functionalities. In case of distributed real-time systems there are two characteristic features of great importance: reliability and temporal characteristics. High reliability level may be achieved by implementation of redundancy. However, every additional element in the system, also the redundant one, influences its temporal characteristic, one of which is the response time critical for the operation of Networked Control Systems. In the following chapter a system with cost effective computing unit redundancy operating in hot standby mode is described and analyzed from the point of view of its real-time operation. The possibility of implementation of synchronization routines between the computing units is also considered.

Determining the Usability of Embedded Devices Based on Raspberry Pi and Programmed with CODESYS as Nodes in Networked Control Systems

Since introduction of the Raspberry Pi embedded computers to the market, its popularity is constantly growing. More and more both hardware and software modules are available for that device. One of the later ones is CODESYS development environment, which make it possible to program Raspberry Pi like a regular Programmable Logic Controllers PLC. Using its network interfaces and industrial protocols like Ethercat or Profinet available in CODESYS, too, one could consider using Raspberry as a node in Networked Control System. Posts and opinions shared on Internet forums proofs it. However, one thing should not be ignored – Raspberry has been never intended to be implemented in industrial environment and was not designed as a real-time device. Therefore before practical application of Raspberry Pi, its temporal characteristics should be analyzed. It is the main concern in the following chapter.

Utilization of Redundant Communication Network Throughput for Non-critical Data Exchange in Networked Control Systems

Redundancy is the main method for achieving high reliability level in networked control systems NCSs. It is often applied in network interfaces in order to maintain operability of communication subsystems even when faults occur. In most cases, redundant communication buses realize exactly the same functionality as the initial non-redundant bus. That makes the system more reliable but the additional throughput of the redundant buses is not exploited even if the system condition would allow it. The idea of taking advantage of that throughput had made the authors to work on multi-network interface node which on the other hand maintain the high reliability of the communication subsystem, and on the other, makes it possible to manage the additional communication resources more efficiently, and therefore increases some parameters of the communication network.