MQTT is a widely used application-layer protocol for Internet-of-Things (IoT) and Industrial IoT networks. However, its centralized architecture, which relies on a broker that mediates all data transmissions, can lead to traffic congestion and reduced network capability, particularly in networks with a large number of devices, such as edge networks. This paper proposes an optimized SDN-based real-time MQTT architecture for edge networks, called Multicast Real-Time MQTT (MRT-MQTT) that leverages multicast routing mechanisms to efficiently distribute data while supporting timeliness requirements and minimizing network usage. Extensive emulation experiments show the effectiveness of the proposed approach and its superiority over Direct Multicast-MQTT (DM-MQTT) and Standard MQTT (STD-MQTT). We achieved a reduction in transmission delay of 29% and 23% for QoS=0 and QoS=1, respectively, when compared to DM-MQTT and 55% and 43% compared to STD-MQTT. In this last case, MRT-MQTT also reduced network usage by 58.0% and 45.0% for QoS=0 and QoS=1, respectively.

Nowadays, custom components are increasingly being replaced by commercially available off-the-shelf hardware and standard protocols. Additionally, emerging industrial paradigms like Industry 4.0 and IoT place new demands on requirements like scalability, transparency, adaptability and efficiency. Accordingly, application layer protocols like the Message Queuing Telemetry Transport Protocol (MQTT) are becoming more and more popular in these fields, thanks to their simplicity, scalability, low resource-usage and decoupling between end nodes. However, these protocols are not deterministic, thus being unsuitable for real-time applications. Recently the authors proposed a set of extensions to the MQTT protocol, allowing applications to explicitly specify real-time requirements that are then used by a resource manager, implemented in Software Defined Networking (SDN), to create real-time channels. This paper extends the work, providing worst-case analysis using the Holistic and Trajectory approaches. The paper also includes a set of experimental results aiming to verify the correctness of both analysis and evaluate its performance in several scenarios.

Circuit modeling of scaffolds based on porcine adipose decellularized extracellular matrix (adECM) doped with reduced graphene oxide (rGO) for spinal cord regeneration is presented. The characteristics of the scaffolds capped with silver electrodes were studied in an aqueous medium through transient and AC analyses. In addition, cyclic voltammetry (CV) plots were obtained. The transient measurements were done using a custom current driver while the CV and AC measurements were obtained with an external impedance analyzer. The results revealed that incorporating rGO reduced the series resistance and the impedance at low frequencies of the scaffold.

Cloud-based architectures are advantageous in aspects such as scalability, reliability and resource utilization efficiency, to name just a few, thus being considered one of the pillars of Industry 4.0. However, in this domain, cloud computing platforms are subject to specific requirements, namely in what concerns real-time performance, determinism and fault-tolerance. This paper focuses on cloud native computing, which is an emerging and promising cloud-computing paradigm, specifically addressing its applicability to real-time systems. Firstly, it introduces the architecture of cloud native applications, discussing their principles, potential advantages and challenges. Then it addresses the opportunities and constraints of such technologies when applied to industrial real-time systems.

MQTT is an application-layer protocol that eventually became popular in the Internet of Things (IoT) and Industrial IoT (IIoT) thanks to its simplicity and effective publisher-subscriber messaging model that enables its use in embedded resource-constrained devices. However, MQTT features a limited set of Quality-of-Service classes addressing exclusively message delivery, impairing its use in IIoT applications subject to timeliness requirements. This limitation of MQTT has been addressed in the literature, but with focus on the broker real-time operation, only. This paper adds to the state-of-the-art, by proposing a set of extensions to the MQTT protocol grounded on Software-Defined Networking (SDN) that enable, at the network level, attaining real-time communication services. Simulation results validate the benefits of the proposed extensions.

The Message Queuing Telemetry Transport (MQTT) protocol is one of the most popular application-layer protocols for machine-to-machine communications. Its popularity results from its simplicity and effective publisher/subscriber messaging model, which allows lightweight implementations able to run on resource constrained devices, thus making this protocol suitable for (Industrial) Internet of Things applications. However, MQTT's Quality-of-Service classes lack support for real-time services, impairing its adoption in applications where data exchanges are subject to timeliness requirements. This limitation was addressed in the literature, but contributions have been focused essentially on the broker software operation. This paper complements these works, presenting a comprehensive set of extensions to the MQTT protocol that aim at supporting real-time semantics and services at the network level. This paper presents the set of extensions as well as a preliminary proof-of-concept implementation, based on MQTT-SN. Preliminary results show the feasibility of the approach, being observed significant improvements on the traffic timeliness.

The concept of Smart Homes has been around for decades, but is gaining momentum nowadays thanks to the dissemination and exponential growth of Internet of Things technologies. However, the logic integration and holistic management of all devices within a home, despite appealing, brings significant technical challenges. Particularly, tasks such as problem diagnosis or energy consumption optimization are becoming increasingly complex. The supervision networking infrastructure plays here a crucial role and is particularly challenging because smart homes combine characteristics commonly found both at the industrial and domestic level. This paper introduces a wireless communication protocol that has been specifically designed for supporting optimization and fault diagnosis systems for smart homes. As distinctive features, the protocol combines determinism and reliability with an high level of adaptivity and flexibility, which are often regarded as conflicting requirements and are not jointly supported, in an effective way, by current state of the art protocols. The paper includes preliminary experimental results that validate some of the desired properties of the protocol.

In recent years it has become common the existence of numerous electronic devices installed in residential spaces as part of home automation solutions. The information given by them such as occupation of spaces, energy consumption, indoor and outdoor temperature, humidity, solar radiation or state of shading systems, combined with external information sources such as weather forecasts can be efficiently used to automate various aspects of a house environment, such as climatic systems. The present work tackles this challenge, by developing an intelligent room temperature control system based on two different approaches: firstly using a Pole-Placement controller and, alternatively, using the principles of Model-based Predictive Control. Such methods provide the support for two implementations of a self-learning and real-time adaptive control system which are validated using both in simulated environment conditions and in a real-world implementation.

Industry 4.0, Industrial Internet of Things, Cyber-Physical Production Systems and Smart Factories are closely related emerging concepts expected to drive significant improvements in industrial production systems, with gains in efficiency, cost and customer satisfaction. These concepts are intimately associated with highly distributed and cooperative architectures that rely, naturally, on the network infrastructure. However, traditional industrial communication technologies hardly provide the required level of integration, flexibility and performance. Seeking a solution to this mismatch, we assess two technologies that appeared recently in the industrial realm, namely IEEE 802.1 Time-Sensitive Networking (TSN) and Software-Defined Networking (SDN). TSN and SDN are fundamentally different, thus having distinct strengths and weaknesses. This paper reviews their fundamental operation principles, evaluating them qualitatively against the specific requirements posed by Industry 4.0.

Emerging concepts such as Smart Production, Industrial Internet of Things and Industry 4.0 bring a radically new set of requirements to the way industrial systems are engineered. In what concerns the communication infrastructure, support to dynamic environments, interoperability and heterogeneity, combined with a significant increase in the number of devices, are just a few of the challenges that must be faced. Software-defined networking is a disruptive networking paradigm that emerged on campus networks but was soon considered for use at industrial level. This paper presents a set of extensions to the Software Defined Networking (SDN) OpenFlow protocol that complement its functionality, namely supporting real-time reservations, which is one of its more notorious limitations when considering industrial scenarios. We explain how the extensions are implemented in the OpenFlow side and enforced using a Flexible Time-Triggered Ethernet network. The extensions are validated experimentally, showing that the platform supports dynamically reconfigurable heterogeneous traffic classes.

The papers in this special section focus on telecommunication services in automation applicaitons. The evolution of automation systems has always been the result of continuous improvements to state-of-the-art systems, occasionally punctuated with significant paradigm and architectural changes that acted as innovation drivers. This happened with the industrial revolutions, which had in their origin the appearance of disruptive technologies, such as the steam engine and machine tools (first industrial revolution); electrification, mass production, and assembly lines (second industrial revolution); use of microprocessors and software (third industrial revolution).

The Vehicular Time-Triggered Protocol (V-FTT) is an infra-structured communication protocol for vehicular communications, based on IEEE802.11p/ETSI ITS-G5 standards, that brings improved timeliness and determinism by taking advantage of cooperative roadside units interconnected by a backhauling network. In a previous work, the use of a Spatial TDMA framework (STDMA) to improve both coverage and communication reliability on V-FTT networks was proposed. A set of experiments, carried out in a real scenario, proved that STDMA brings coverage and reliability improvements but with limitations. Particularly, the obtained results show that in order to obtain low message error rates, a prohibitively high number of roadside units may be required. Selective message retransmission is a well-known time-domain redundancy technique, which has been also explored for vehicular communications. However, the simultaneous combination of both space- and time-domain techniques has yet to be explored. This paper presents a preliminary study of the potential benefits of such approach. Data extracted from an experimental system deployment in a Portuguese highway was used to derive a realistic error-rate model. Based on this model, simulations were carried out to assess and validate the potential benefits of such hybrid approach.

Modern distributed real-time embedded applications have high processing requirements associated with strict deadlines. For some applications, such constraints cannot be fulfilled by existing single-core embedded platforms. A solution is to parallelize the execution of the applications, by allowing networked nodes to distribute their workload to remote nodes with spare capacity. In that context, this paper presents a holistic timing analysis for fixed-priority fork-join parallel/distributed tasks. Furthermore, we extend the holistic approach to consider the interaction between parallel threads and messages interchanged through a flexible time triggered switched Ethernet network, and we show how the pessimism on the worst case response time computation of such tasks can be reduced by considering the pipeline effect that occurs in such distributed systems. To evaluate the performance and correctness of the holistic model, this paper includes a numerical evaluation based on a real automotive application. The obtained results show that the proposed method is effective in distributing the load by different nodes, allowing a significant reduction of the worst case response time of the tasks. Moreover, the paper also reports an implementation of the model on a Linux library, called parallel/distributed real-time, as well as the corresponding results obtained on a real testbed. The obtained results are in accordance with the predictions of the holistic timing analysis.

Automation systems are composed of tightly integrated mechanical, electronic, and computer equipment being designed to reduce or even eliminate the need for human intervention in the realization of many different tasks. Also, the automation of systems and processes is often characterized by some interesting features, such as reduced exploration costs and intrinsically higher efficiency, safety, and quality. The papers in this special focus on the use of automation in communication systems.

IIoT (Industrial Internet of Things) cloud applications require reliable, fault-tolerant networks, supporting real-time guarantees and allowing interaction with other applications already existing in the datacenter. The Software Defined Networks (SDN) paradigm is especially suited for the management of the network cloud because of its fine grained admission control and the management flexibility provided by the centralized resource management. This paper presents a SDN management approach for IIoT datacenters, which provides an efficient fault-tolerant network, enabled with deterministic QoS guarantees. By taking advantage of a centralized resource management mechanism, the proposed solution integrates topology definition with resource allocation, allowing to efficiently distribute available network resources for admitted packet flows.

Industrial Internet and Industrial Internet of Things are emerging concepts that concern the use of Internet technologies on industrial environments. The main objective of such architectural visions is allowing a tight and seamless integration between all the functional units and layers that compose industrial processes, from the lowest levels (e.g. field-level devices such as sensors and actuators) to the higher layers, including management, logistics and maintenance. This kind of architecture promises, among other advantages, improving efficiency and flexibility, reduce installation and maintenance costs and reduce unplanned downtime. However, industrial processes often encompass functionalities like closed-loop control of physical processes that are highly critical and have strict timeliness requirements. These requirements are not satisfied by normal Ethernet-based systems. Standards such as IEEE AVB and TSN are addressing this problem, enhancing the real-time properties of Ethernet. However, considering the information presently available, such standards still present some limitations and inefficiencies. This paper reports the extension of HaRTES, an Ethernet-based real-time architecture originally developed for use at the lower layers of industrial scenarios, with MAC Bridge standard functionalities, to make it capable of being integrated on Industrial Internet of Things frameworks. The paper also presents preliminary results obtained with a prototype realization of the extended HaRTES switch.

This paper presents a holistic timing analysis for fixed-priority fork-join Parallel/Distributed tasks (P/D tasks) over a Flexible Time Triggered - Switched Ethernet (FTT-SE) network. The holistic approach considers both time-triggered and event-triggered tasks/messages.

On-the-fly adaptability and reconfigurability are recently becoming an interest in real-time communications. To assure a continued real-time behavior, the admission control with a quality-of-service mechanism is required, that screen all adaptation and reconfiguration requests. In the context of switched Ethernet networks, the FTT-SE protocol provides adaptive real-time communication. Recently, we proposed two methods to perform the online reconfiguration in multi-hop FTT-SE architectures. However, the methods lack the experimental evaluation. In this paper, we evaluate both methods in terms of the reconfiguration time.

Distributed systems rely in communication networks, typically a bus, in order to exchange messages and fulfill their goals. However, message transmission is subject to interferences that ultimately can lead to message corruption. In systems where a high-reliability is sought, error recovery mechanisms can be deployed in order to give the required reliability level, and this can be done in the spatial or temporal domain. In the scope of the FTT paradigm, and applied to the FTT-CAN protocol, the authors have previously presented a time domain recovery method using message retransmissions controlled by a server. In this article we assess the impact of different scheduling policies for the server, presenting a qualitative evaluation of the alternatives, complemented by a simulation study, in order to verify their advantages and weak points.

In safety-critical systems a global high-reliability is sought, including in the communication network when a distributed control system is used. The FlexRay protocol was developed within the automotive industry with the necessary characteristics to respond to the demands of safety-critical applications, e.g. X-by-wire. Nevertheless, the FlexRay protocol does not define a mechanism to guarantee message delivery, nor defines global error signaling, leaving the resolution of these problems to the application. This paper presents a preliminary proposal for a mechanism that uses temporal redundancy to recover transient errors in time-triggered messages. An extra node is used to trigger message retransmissions whenever errors or omissions do effectively occur. This mechanism uses the FlexRay dynamic segment to implement message retransmissions, leading to a minimum recovery time, typically one cycle, together with a very small bandwidth usage.

In the context of switched Ethernet networks, multi-hop communication is essential as the networks in industrial applications comprise a high amount of nodes, that is far beyond the capability of a single switch. In this paper, we focus on multi-hop communication using HaRTES switches. The HaRTES switch is a modified Ethernet switch that provides real-time traffic scheduling, dynamic Quality-of-Service and temporal isolation between real-time and non-real-time traffic. Herein, we propose a method, called Reduced Buffering Scheme, to conduct the traffic through multiple HaRTES switches in a multi-hop HaRTES architecture. In order to enable the new scheduling method we propose to modify the HaRTES switch structure. Moreover, we develop a response time analysis for the new method. We also compare the proposed method with a method previously proposed, called Distributed Global Scheduling, based on their traffic response times. We show that, the new method forwards all types of traffic including the highest, the medium and the lowest priority, faster than the previous method in most of the cases. Furthermore, we show that the new method performs even better for larger networks compared with the previous one.

Flexible Time-Triggered communication (FTT) allows a distributed embedded system (DES) to adapt to changing real-time requirements at runtime. This facilitates the continuous operation of the DES under dynamic environments that change over time. However, for continuous operation, high reliability in the nodes of the DES is also crucial. This can be achieved using node replication, as long as failure independence between replicas is ensured, which calls for preventing the propagation of errors. Our goal is to prevent the propagation of Byzantine node behaviours and to ensure that local errors in the channel cannot disturb the global communication. For this, we construct the HaRTES/PG switch, a new switch based on the HaRTES implementation of FTT for Ethernet. This paper presents as a first step a study of the possible errors that may lead to Byzantine node behaviours and a global communication disturbance in HaRTES, as well as some ideas on how to prevent the propagation of these errors in HaRTES/PG.

Over the last few years the problem of optimal estimation and control over lossy networks has been studied in detail. However, most of such works assume that in the absence of a new actuation value, the actuator either outputs zero or the previous value. Some other extensions have been proposed, but they present similar limitations. This paper shows that this method is not optimal and presents a new approach, in which the controller sends a number of predictions of future actuation values, which are outputted when the actuator does not receive a new message. Under this new assumption it is shown that the controller/estimator herein presented performs equal to or better than any previously introduced controller, being the equality verified only in the absence of communication errors. A modified Kalman filter as well as a specific optimal controller for this novel actuation model are also presented.

Distributed Embedded Systems are subject to transient communication faults that need being detected and mitigated in safety-critical scopes. This paper addresses error recovery in time-triggered systems based on the Controller Area Network (CAN). It extends a recent work that proposed using online traffic scheduling, combined with servers, to implement dynamic message retransmissions. In particular, we provide a schedulability analysis that considers the interference of the error-recovery server in the time-triggered traffic, as well as a methodology to compute the worst-case response time of messages affected by errors. We also present a comparison with related error-recovery methods that confirms the superiority of the proposed method.

Video applications, which include industrial uses like machine vision, object tracking, surveillance, driving aids, etc. are becoming increasingly common. These sensors produce large amounts of data, being normally compressed at the source nodes to save network bandwidth. As a side effect, video streams exhibit a large variability in their bandwidth utilization. On the other hand, many video applications are highly dynamic. For instance, a video surveillance application can meet its goals with a low frame-rate video, when the environment being monitored is static, but require an high frame-rate when the environment changes. Another example is applications that have several video sources that are activated on demand. For instance, a rear-view video camera, nowadays commonly found in cars and trucks, is only necessary during certain maneuvers. Applications like the ones presented above can be efficiently supported by enhanced Ethernet switching that provides hierarchical server-based traffic scheduling, in particular by the FTT-enabled switch [1] [2] that resulted from instantiating the FTT (Flexible Time-Triggered) communication paradigm [3] onto a customized Ethernet switch. Servers are, in fact, adequate abstractions to handle real-time video transmission since:1) servers discipline the use of the network, thus coping with the large variability of compressed video sources, 2) the adaptability, obtained by changing the servers budget, permits varying dynamically the bandwidth allocated to each video stream, 3) the reconfigurability permits enabling and disabling video-streams. We demonstrate these features with a simplified video surveillance demo, using the setup shown in Figure 1.

The problem of optimal control given full state knowledge has been solved many years ago and is very well documented. Nonetheless, in most control settings it is virtually impossible to know the exact state value. To deal with this fact, two concepts were introduced: certainty equivalence and separation principle. In this paper, it is presented a novel necessary condition for certainty equivalence to hold, without such condition, in the presence of state uncertainty current optimal controllers lead to suboptimal control. Furthermore, it is also presented a novel controller that remains optimal even when the necessary condition in question is violated. takes into account the effect of the sate estimation error in the control. It is proven that the the new controller is never outperformed by classical approaches.

The complexity of Networked Embedded Systems (NES) has been growing steeply, due to increases both in size and functionality, and is becoming a major development concern. This situation is pushing for paradigm changes in NES design methodologies towards higher composability and flexibility. Component-oriented design technologies, in particular supported by server-based scheduling, seem to be good candidates to provide the needed properties.

The Flexible Time-Triggered communication over Switched Ethernet protocol (FTT-SE) was proposed to overcome the limitation of guaranteeing the real-time communication requirements of conventional switches, and at the same time to support reconfiguration of dynamic adaptive systems. The protocol fragments large messages into a sequence of packets that are individually scheduled. The maximum transmission unit (MTU), that restricts the packets size, has a significant effect on the schedulability of the packets. In this paper, we investigate the problem of selecting the optimal MTU size that maximizes the schedulability of real-time messages. We propose two algorithms to find optimal/sub-optimal values of MTU; the first one finds an optimal solution but exhibits high computational complexity, while the second one is sub-optimal but exhibits a lower computational complexity. Finally, we evaluate our proposed algorithms by means of simulation studies and compare their results with the results of assigning MTU to the maximum packet size that the protocol can allow.

Industrial media control applications require on-line QoS management services to dynamically allocate the bandwidth among the entities that compose the distributed application. The bandwidth distribution mechanism assigns bandwidth to each entity based on the QoS requirements and the current state of the network. However, mapping that bandwidth into operational parameters that serve the scheduling model of the network is not straightforward. Due to systems constraints, this is not a bijective function, therefore multiple solutions may mathematically represent the same bandwidth value but lead to different application performance levels. This paper presents two mapping algorithms and analyzes their performance in this context. The obtained results show that the selection of this mapping algorithm is highly relevant for the application performance.

Dynamic resource management is generating growing interest as a way to simplify systems deployment, react to changing operational conditions and improve efficiency in using system resources. Buttazzo et al proposed the elastic task model (ETM) that dynamically moves the tasks instantiation period around a nominal value, increasing or decreasing the bandwidth that each task uses from the resource. However such computation requires a number of iteration steps. This paper identifies the QoS-based resource distribution problem and proposes a generic framework that encompasses the ETM. An algorithm is presented for the resource distribution that computes the results in minimum time, outperforming the original ETM scheme in terms of computational complexity.

Ethernet switches are typically found in many large-scale distributed real-time systems providing low-end transactions as well as bulk backbone routing to real-time applications. The FTT-SE protocol (Flexible Time-Triggered communication over Switched Ethernet) is a recent proposal to bypass the limitations of conventional switches in terms of real-time behavior while catering for growing requirements on dynamic reconfigurability and adaptability. For this end, this paper develops linear time-complexity and memory-efficient on-line admission control tests based on utilization bounds for Rate-Monotonic and EDF scheduling on Ethernet switches using FTT-SE, which are suited for dynamic Quality of Service (QoS) management. Our analysis also has broader applicability in general periodic task sets with bounded release delays. For FTT-SE with 100 Mbps links and 1500 bytes of maximum packet size, our sufficient schedulability condition achieves an utilization bound of 61% for RMS and 88% for EDF. Simulation results on randomly generated task sets demonstrate that such bounds are within 18% and 5% utilization of the ideal tests for RMS and EDF, respectively.

The middleware is an important software component when designing an application, facilitating the development and deployment of the applications. In the case of Distributed Embedded Systems (DES), the middleware should provide basic functionalities to abstract the complexity that results from network distribution, namely data consistency, events synchronization and resource management. Often DES applications exhibit real-time requirements and have to deal with dynamic environments that present evolving requirements. While some middleware architectures have been proposed to address resource provisioning and QoS management, none of those middle-wares supports dynamic resource reconfiguration while providing real-time guarantees. This paper proposes a middleware layer, based on the services provided by a flexible real-time communication protocol, addressing distribution abstraction, dynamic reconfiguration and dynamic QoS management under real-time constraints.

Ethernet is becoming a common network technology for industrial and factory automation systems and, in recent years, a big effort has been made in enabling real-time communications using Ethernet technology. Many of these systems are complex, extend over relatively large places and/or integrate a significant number of nodes, thus requiring the use of multiple switches (hop). In this paper we look into the usage of Flexible Time-Triggered (FTT) enabled Ethernet switches in this class of systems, more specifically using the recently proposed server-based scheduling mechanism supported by this protocol. The paper proposes and validates a resource reservation protocol, presents a method for computing the end-to-end deadlines and discusses possible strategies for the deadline partitioning.

Road accidents have a dramatic social and economic impact on the society, a situation that fostered the research of mechanisms for increasing road safety. Many of these mechanisms require the ability of the vehicles to communicate among each other and/or with fixed road-side stations. Due to the inherent mobility constraints, wireless technologies play a central role in this type of applications. Despite having been originally developed to delivery last mile wireless broadband access, as an alternative to cable and DSL, WiMAX presents some attractive attributes, such as quality-of-service management and traffic differentiation that are well suited for use in traffic applications. Nevertheless, to the best of our knowledge, no research in this area has considered the use of this technology. Thus, this WIP presents a preliminary study and assessment of the WiMAX technology for vehicular communications usage.

In recent years, approaches to control performance and resource optimization for embedded control systems have been receiving increased attention. Most of them focus on theory, whereas practical aspects are omitted. Theoretical advances demand flexible real-time kernel support for multitasking and preemption, thus requiring more sophisticated and expensive software/hardware solutions. On the other hand, embedded control systems often have cost constraints related with mass production and strong industrial competition, thus demanding low-cost solutions. In this paper, it is shown that these conflicting demands can be softened and that a compromise solution can be reached. We advocate that recent research results on optimal resource management for control tasks can be implemented on simple multitasking preemptive real-time kernels targeting low-cost microprocessors, which can be easily built in-house and tailored to actual application needs. The experimental evaluation shows that significant control performance improvement can be achieved without increasing hardware costs.

In this paper we overview the integration of a framework that generically manages the system resources in the form of contracts, namely the FRESCOR framework, with a flexible network resource. We describe how a network resource, namely FTT-SE, supports the FRESCOR framework services and, likewise, how the network services are made available to the application through the contracting framework. In a designer perspective, we also describe how a typical distributed application can be easily deployed using such a framework.

The use of multimedia within industrial applications has become commonplace, targetting improved process monitoring and machine vision. In both cases, the multimedia information is commonly distributed and subject to time constraints that must be met across networks while avoiding untolerable interference over typical control flows. This can be achieved with Constant Bit-Rate (CBR) channels, typically supported by real-time protocols. However, the compressors used to reduce the amount of information to transfer generate Variable Bit-Rate (VBR) patterns. Adapting a VBR source to a CBR channel requires specific care in order to avoid wasting channel bandwidth or dropping video frames. This paper focuses on MJPEG transmission over Ethernet and proposes a bidimensional adaptation using the JPEG quantification factor q on the source side and frame acquisition/transmission period T on the source/network side respectively, using the FTT-SE protocol and its support for dynamic QoS management. The paper also shows several experiments with pre-recorded video streams that illustrate the advantages of the proposed approach.

This paper presents a fault-tolerant modular control architecture for an electrical vehicle (VEIL) equipped with x-by-wire sub-systems. The proposed architecture is based on COTS components and includes steer-by-wire, brake-by-wire and accelerate-by-wire safety critical functions. The communication infrastructure is based on the FTT-CAN protocol, which provides the joint scheduling of message and tasks, according to a holistic approach.

The traditional approaches to the design of distributed safety-critical systems, due to fault-tolerance reasons, have mostly considered static cyclic table-based traffic scheduling. However, there is a growing demand for operational flexibility and integration, mainly to improve efficiency in the use of system resources, with the network playing a central role to support such properties. This calls for dynamic online traffic scheduling techniques so that dynamic communication requirements are adequately supported. Nevertheless, using dynamic traffic management mechanisms raises additional problems, in terms of fault-tolerance, related with the weaker knowledge of the future system state caused by the higher level of operational flexibility. Such problems have been recently addressed in the scope of using flexible time-triggered CAN (FTT-CAN) in safety-critical applications in order to benefit from the high operational flexibility of this protocol. This paper gathers and reviews the main mechanisms that were developed to provide dependability to the protocol, namely, master replication and fail-silence enforcement.

This paper presents a new method to allow more flexibility on the scheduling of messages across a fieldbus in overload situations. The method proposes the on-line adaptation of the sampling period to the bus load, trying to keep it as low as possible during overloads. The sampling period is allowed to change inside an interval corresponding to 4 to 10 samples per rise time. To assess the solution herein presented, a distributed adaptive control system was implemented in TrueTime, using the FTT-CAN protocol, for the communication infrastructure, a pole-placement controller and a model for the identification of plant parameters that takes into account the network-induced jitter

Ethernet was not originally developed to meet the requirements of real-time industrial automation systems and it was commonly considered unsuited for applications at the field level. Hence, several techniques were developed to make this protocol exhibit real-time behavior, some of them requiring specialized hardware, others providing soft-real-time guarantees only, or others achieving hard real-time guarantees with different levels of bandwidth efficiency. More recently, there has been an effort to support quality-of-service (QoS) negotiation and enforcement but there is not yet an Ethernet-based data link protocol capable of providing dynamic QoS management to further exploit the variable requirements of dynamic applications. This paper presents the FTT-Ethernet protocol, which efficiently supports hard-real-time operation in a flexible way, seamlessly over shared or switched Ethernet. The FTT-Ethernet protocol employs an efficient master/multislave transmission control technique and combines online scheduling with online admission control, to guarantee continued real-time operation under dynamic communication requirements, together with data structures and mechanisms that are tailored to support dynamic QoS management. The paper includes a sample application, aiming at the management of video streams, which highlights the protocol's ability to support dynamic QoS management with real-time guarantees.

As the bandwidth of CPUs and networks continues to grow, it becomes more attractive, for efficiency reasons, to share such resources among several applications with the minimum level of interference. This can be achieved using temporal partitions, with each application assigned to its own partition and executing as if it was executing alone on a resource with lower bandwidth. The partitions are associated to servers that execute the application tasks according to a given application-level scheduler. On the other hand, the set of servers is scheduled by a system-level scheduler. This paper addresses the particular case of fixed priorities-based application-level schedulers together with a periodic server model at the system level. It starts with an adequate response time analysis based on the notion of server availability for a known server. Then it addresses the inverse problem of designing a server with minimum system-level resource requirements to fulfill the application time constraints. In this context, the paper shows that response time based schedulability tests with linear time bounds do not need to consider all tasks but just a small subset, which may lead to substantial speed-ups. The proposed method goes a step further with respect to other recent works in the literature by considering a more complete task model, effectively computing the server parameters and establishing a better trade-off concerning complexity and tightness.

Summary form only given. Real-time distributed application complexity is steadily increasing. A well-known technique used to manage such complexity consists of decomposing the whole system into different quasiindependent distributed subsystems. Inter-subsystem communication, when necessary, is performed via gateway nodes that filter ingoing and outgoing traffic. For real-time systems, this architecture poses additional design challenges, since it becomes necessary to consider both intra and inter-network message exchanges with real-time constraints. The FTT communication paradigm has been provided with tools for supporting flexible real-time communication on isolated networks. We present an approach to incorporate multisegment support into the FTT protocol family. Two approaches are presented, analyzed and compared, which allow breaking end-to-end deadlines into parameters that are local to each one of the interconnected networks.

Despite having been designed to interconnect office equipment such as computers and printers, since its early daysEthernet has also been considered for use in the industrial domain. However, it was not originally developed to meet the requirements of real-time industrial automation systems and it was commonly considered unsuited for applications at the field level, i.e.to interconnect sensors, actuators and controllers. Therefore, along its 30 years of existence, several proposals have been presented to make this protocol exhibit real-timebehaviour. Nevertheless, these proposals either require specialised hardware, or are suited to soft-real-time operation only, or are bandwidth or response-time inefficient. This paper presents an overview about the work previously done towards real-time communication on Ethernet. Then, it presents a new protocol, FTT-Ethernet, which relies on common network adapters and on a new transmission control named master/multi-slave that efficiently supports hard-real-time operation in a flexible way.

The requirement for flexible operation is becoming increasingly important in many distributed computer controlled systems, in order to cope with dynamic operational changes in a resource efficient way. This requirement naturally extends to the low level of such systems where, typically, field equipment such as sensors, actuators and controllers, are interconnected by a fieldbus communication system. The paper presents the DISCO project (DIStributed embeddable systems for COntrol applications) that started in September 2000, in the University of Aveiro, aiming at exploring specification, architectural and management issues in flexible distributed computer control systems for embedded applications. The project addresses the issues of control requirements definition in a QoS perspective, flexible scheduling of both network traffic as well as nodes' computing load, and global system management techniques. The paper shows the results obtained so far as well as the status of the current work in the scope of the DISCO project.