Many safety-critical real-time applications are implemented using distributed architectures, composed of heterogeneous processing elements interconnected in a network. Our focus in this paper is on the TTEthernet protocol, a deterministic, synchronized and congestion-free network protocol based on the Ethernet standard and compliant with the ARINC 664 Specification Part 7. TTEthernet is highly suitable for safety-critical real-time applications since it offers separation for messages using the concept of virtual links and supports three time-criticality classes: Time-Triggered (TT), Rate-Constrained (RC) and Best-Effort. In this paper we are interested in the design optimization of TTEthernet networks used to transmit real-time application messages. Given the set of TT and RC messages, and the topology of the network, our approach optimizes the packing of messages in frames, the assignment of frames to virtual links, the routing of virtual links and the TT static schedules, such that all frames are schedulable and the worst-case end-to-end delay of the RC messages is minimized. We propose a Tabu Search-based metaheuristic for this optimization problem. The proposed algorithm has been evaluated using several benchmarks.

http://www2.compute.dtu.dk/~paupo/publications/Tamas-Selicean2015aa-Design%20Optimization%20of%20TTEther-Real-Time%20Systems%20Journal.pdf

Design optimization of TTEthernet-based distributed real-time systems

Software-Defined Networking (SDN) is a promising approach to build future industrial networks. The disruptive change of network architecture and management opens new possibilities in various application domains. While the approach is already deployed in several domains and was also initially examined to be used in the industrial area, many open questions arise when assessing the risks and improvements to be expected. The following work presents features of a potential future industrial network infrastructure and sets up requirements that are important for future communications. It reviews basics of SDN and correlates existing work to the specified requirements. Finally, it presents open questions and room for future research.

Analysis of realizing a future industrial network by means of Software-Defined Networking (SDN)

In the future, production systems will consist of modular and flexible production components, being able to adapt to completely new manufacturing processes. This requirement arises from market turbulences caused by customer demands, i. e. highly customized goods in smaller production batches, or phenomenon like commercial crisis. In order to achieve adaptable production systems, one of the major challenges is to develop suitable autoconfiguration mechanisms for industrial automation systems. This paper presents a two-step architecture for the autoconfiguration of real-time Ethernet (RTE) systems. As a first step, an RTE-independent device discovery mechanism is introduced. Afterwards, it is shown how the parameters of an RTE can be configured automatically using Profinet IO as an exemplary RTE system. In contrast to the existing approaches, the proposed discovery mechanism is based on the OPC Unified Architecture (OPC-UA). In addition, a procedure to autoconfigure modular IO-Devices is introduced.

Using OPC-UA for the autoconfiguration of real-time Ethernet systems

In contrast to the predecessors, the fifth generation of mobile networks (5G) will particularly address communication in production systems by providing machine-type communication and matching requirements regarding reliability and latency. However, 3GPP 5G will not be the one and only network technology that can be used to fulfill all the requirements raising from industrial applications at reasonable costs. It is more likely, that it complements other wired and wireless technologies, rather than replacing them. This paper presents different scenarios to combine 5G and Industrial Ethernet to a hybrid topology, it explains the characteristics and possible use cases for these scenarios and it sketches approaches to engineer and configure the hybrid network.

Towards integration of Industrial Ethernet with 5G mobile networks

Thanks to the standards being developed by IEEE Time-Sensitive Networking (TSN) Task Group, the classical IEEE 802.1 Ethernet architecture is now enhanced to accommodate real-time and safety-critical requirements emerging in various cyber-physical systems. The deterministic nature of the communication is achieved through the time-triggered traffic, which requires introducing strict scheduling constraints that may be an obstacle in finding a feasible schedule. In this article, we propose a simple hardware enhancement of a switch along with a relaxed scheduling constraint that increases schedulability and throughput of the time-triggered traffic but maintains the deterministic nature and timeliness guarantees in a TSN network. We give a formal proof to justify the claims and an algorithm benchmarking and experimental validation to demonstrate the gains. The results show that the number of flows that can be scheduled in the model with the relaxed constraint is on average by 75.1 % larger than in the traditional model.

Enhancing Schedulability and Throughput of Time-Triggered Traffic in IEEE 802.1Qbv Time-Sensitive Networks

Scheduling of the communication in industrial networks takes time. Since it has to be carried out every time a new network is brought to work, the time necessary to perform scheduling becomes a prominent factor. The approach presented in this paper, simplifies the scheduling problem of PROFINET IRT by resolving communication conflicts by utilization of the dynamic frame packing (DFP) mechanism.

Fast and simple scheduling algorithm for PROFINET IRT networks

Many aspects have to be considered while achieving flexibility of production systems. One of them is flexible communication system that on one hand fulfils requirements of a particular industrial application and on the other hand allows integration of new network components optimally in a seamless way. In this paper, an approach to increase, rather static, Time Triggered Ethernet based systems is proposed. It is based on a greedy scheduling approach that can be implemented directly in a processing limited hardware such as IO Controller. This, together with the discovery and auto configuration mechanism proposed in [1] allows to shift the engineering process typically performed offline using engineering tool to the field level. Furthermore, it has been proven that the proposed scheduling approach is not only simple but also powerful. It is able to calculate an optimal schedule for any kind of tree graph and the complexity of the algorithm is defined by the complexity of the used sorting algorithm.

Increasing flexibility of Time Triggered Ethernet based systems by optimal greedy scheduling approach

The evolution of industrial communication inexorably moves towards Ethernet based networks. One important reason for using Ethernet at the shop floor is to participate on the continuous advancements of standard Ethernet. In contradistinction to the star topology, used commonly in home and office networks, in the industrial automation most common network structure is line. It is due to the fact that it simply follows the architecture of plants (production line). Depending on the size of an automation facility the size of such a network structure may contain up to 100 nodes. Thus, the node to node synchronization jitter, with its cumulative behavior, becomes a relevant performance factor for high demanding applications such as motion control. This paper examines influence of the synchronization jitter on the industrial Ethernet networks by taking the example of PROFINET IO, a common representative of an industrial Ethernet based protocol. It uses a Time Division Multiple Access (TDMA) procedure together with the communication scheduling to fulfill hard real-time requirements. Additionally the protocol uses Dynamic Frame Packing (DFP) in order to optimize bandwidth utilization. The efficiency of both mechanisms strongly depends on the node to node synchronization accuracy.

Node to node synchronization accuracy requirements of Dynamic Frame Packing

The invention relates to a communication system (5) which has a PROFINET IRT system (40) with first communication devices (50, 60) for isochronous transmission. In order to also allow a conventional standard Ethernet communication device (10) to transmit real-time-critical data via the PROFINET IRT system (40), a specific IRT bridge device (30) is provided. The bridge device (30) has a timer (34), which is synchronized with the timers (57, 67) of the first communication devices (50, 60) in time. Furthermore, a device (31) is provided for evaluation of the transmission time of a real-time-critical data message which is received from the communication device (10), and a control device (33) is provided which controls the passing on of the associated real-time-critical data message to at least one second communication device (50, 60) depending on the evaluated transmission time.

Communication system and method for isochronous data transmission in real time

One of the most important requirements for the industrial networks, apart from the real-time capability, is the reliability. There are several methods that can be used to increase the communication reliability. One of them is data duplication, which is afterwards transmitted using two different (disjoint) paths. Since, such path search for time triggered Ethernet based systems is typically done during engineering, it is important to keep the time needed for that as short as possible. Especially, if some topology changes are foreseen causing system re-engineering. Therefore in this paper an algorithm is proposed that has linear time complexity and is able to find two possibly disjoint paths for an arbitrary network topology in a short time.

Markus Schumacher

Papers

Fast and simple scheduling algorithm for PROFINET IRT networks

Increasing flexibility of Time Triggered Ethernet based systems by optimal greedy scheduling approach

Node to node synchronization accuracy requirements of Dynamic Frame Packing

Communication system and method for isochronous data transmission in real time

Linear time, possibly disjoint path search approach for ethernet based industrial automation networks