pp.bib
@inproceedings{MIFDAOUI_RTN_2012,
author = {Mifdaoui, A. and Behnam, M. and Nolte, T. and Pedreiras, P. and Almeida, L. and Marau, R.},
title = {Exploring alternatives to use master/slave full duplex switched Ethernet for avionics embedded applications},
booktitle = {11th International Workshop on Real-Time Networks (RTN'2012) Proceedings},
year = {2012},
editor = {},
volume = {},
series = {},
pages = {},
address = {Pisa, Italy},
month = {July},
organization = {},
publisher = {},
doi = {},
issn = {},
isbn = {},
keywords = {Real-Time communications, FTT, Ethernet, Avionics},
note = {},
key = {},
abstract = {The complexity of distributed real-time systems, including military embedded applications, is increasing due to an increasing number of nodes, their functionality and higher amounts of exchanged data. This higher complexity imposes major development challenges when nonfunctional properties must be enforced. On the other hand, the current military communication networks are a generation old and are no longer effective in facing such increasingly complex requirements. A new communication network, based on Full Duplex Switched Ethernet and Master/slave approach, has been proposed previously. However, this initial approach is not efficient in terms of network bandwidth utilization. In this paper we propose two new alternative approaches that can use the network bandwidth more efficiently. In addition we provide a preliminary qualitative assessment of the three approaches concerning different factors such as performance, scalability, complexity and flexibility}
}
@inproceedings{SANTOS_DCOSS_2012,
author = {Santos, R. and Pedreiras, P. and Almeida, L.},
title = {Demonstrating an Enhanced Ethernet Switch Supporting Video Sensing with Dynamic QoS},
booktitle = {8th IEEE International Conference on Distributed Computing in Sensor Systems (DCOSS'2012) Demos session},
year = {2012},
editor = {},
volume = {},
series = {},
pages = {293--294},
address = {Hangzhou, China},
month = {May},
organization = {},
publisher = {},
doi = {10.1109/DCOSS.2012.60},
issn = {},
isbn = {978-0-7695-4707-7},
keywords = {Real-Time communications, FTT, Ethernet, FTT-SE},
note = {},
key = {},
abstract = {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}
}
@inproceedings{MARQUES_ICIT_2012,
author = {Marques, L. and Vasconcelos, V. and Pedreiras, P. and Almeida, L.},
title = {Tolerating transient communication faults with online traffic scheduling},
booktitle = {IEEE International Conference on Industrial Technology (ICIT'2012) Proceedings},
year = {2012},
editor = {},
volume = {},
series = {},
pages = {396-402},
address = {Athens, Greece},
month = {March},
organization = {},
publisher = {},
doi = {10.1109/ICIT.2012.6209970},
issn = {},
isbn = {978-1-4673-0340-8},
keywords = {Real-Time communications, FTT, CAN, Embedded systems, Scheduling, x-by-wire systems},
note = {},
key = {},
abstract = {Building distributed embedded systems that will be fault-free for all their lifetime is virtually impossible, thus the systems must deal with them if a continued correct behavior is needed. This is the case of safety-critical systems, such as X-by-wire systems in the automotive domain. Concerning transient communication faults in particular, they can be dealt with at various levels of the protocol stacks, with different techniques, e.g., temporal and spatial redundancy. In this paper we focus on temporal redundancy and we address the limitations imposed by typical time-triggered systems, commonly found in safety-critical systems, arising from their static traffic definition. In these systems the use of temporal redundancy to handle communication errors requires the pre-allocation of communication resources that, in the absence of errors, are wasted. Therefore, we propose an online traffic scheduling approach in which retransmissions are consistently scheduled with the remaining time-triggered traffic, using the unique flexibility provided by the FTT-CAN protocol (Flexible Time-Triggered communication on CAN). We address the integration of appropriate fault detectors in the FTT-CAN protocol to monitor the bus activity and re-schedule omitted messages. We show that this approach is more efficient than the static allocations, since communication resources are only allocated when necessary. We also discuss alternative realizations and validate the approach with initial results from a prototype implementation}
}
@inproceedings{SANTOS_RTSSATWORK_2011,
author = {Santos, R. and Pedreiras, P. and Behnam, M. and Nolte, T. and Almeida, L.},
title = {Demonstrating an Ethernet switch enhanced with hierarchical scheduling},
booktitle = {32nd IEEE Real-Time Systems Symposium (RTSS'2011) Open Demo Session of Real-Time Techniques and Technologies},
year = {2011},
editor = {},
volume = {},
series = {},
pages = {},
address = {Vienna, Austria},
month = {November},
organization = {},
publisher = {},
doi = {},
issn = {},
isbn = {},
keywords = {Embedded systems, NES, Ethernet, Switch, FTT, Real-Time communications, Servers, Scheduling, Quality of Service},
note = {},
key = {},
abstract = {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. As response, we developed a multi-level hierarchical server-based architecture for Ethernet switches that provides composability and supports online adaptation and reconfiguration [1] [2]. This framework exhibits the following features: 1) A hierarchical architecture that supports server composition, virtual real-time channels providing temporal isolation (composability in the time domain); 2) Analytical tools for guaranteed real-time behavior; 3) Simple interface to adapt and reconfigure servers during runtime}
}
@inproceedings{SANTOS_EMSOFT_2011,
author = {Santos, R. and Behnam, M. and Nolte, T. and Pedreiras, P. and Almeida, L.},
title = {Multi-level hierarchical scheduling in Ethernet switches},
booktitle = {11th International Conference on Embedded Software (EMSOFT'2011) Proceedings},
year = {2011},
editor = {},
volume = {},
series = {},
pages = {185--194},
address = {Taipei, Taiwan},
month = {October},
organization = {},
publisher = {},
doi = {},
issn = {},
isbn = {978-1-4503-0714-7},
keywords = {Embedded Systems, NES, Ethernet, Switch, Analytical models, Bandwidth, Protocols, Real time systems, Servers, Time factors},
note = {},
key = {},
abstract = {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. As a response we developed a multi-level hierarchical server-based architecture for Ethernet switches that provides composability and supports online adaptation and reconfiguration. This paper extends our work, presenting the associated response-time based schedulability analysis, necessary for the admission control procedure. Additionally, we have derived the temporal complexity of the analysis, which is shown to be O(n2), where n is the number of higher priority components associated with a given server. Finally, we present a proof-of-concept implementation and a set of experimental results that validates the analysis}
}
@inproceedings{MARQUES_INFORUM_2011,
author = {Marques, L. and Vasconcelos, V. and Pedreiras, P. and Almeida, L.},
title = {Towards Efficient Transient Fault Handling in Time-Triggered Systems},
booktitle = {INFORUM - Simp\'{o}sio de Inform\'{a}tica},
year = {2011},
editor = {},
volume = {},
series = {},
pages = {},
address = {Coimbra, Portugal},
month = {September},
organization = {},
publisher = {},
doi = {},
issn = {},
isbn = {},
keywords = {CAN, FTT-CAN, Scheduling, Real-Time communications},
note = {},
key = {},
abstract = {Transient communication faults in distributed control systems (DCS) are unavoidable but must be handled adequately in order to enforce correct system behaviour. A typical way of handling transient faults is temporal redundancy by means of retransmissions. However, DCS are frequently designed with time-triggered architectures, being scheduled offline and not coping efficiently with retransmissions as these require the pre-allocation of bandwidth that, in the absence of errors, is wasted. In this paper we propose using the Flexible Time-Triggered paradigm to reconcile the Time-Triggered model with on-line scheduling of retransmissions when needed, only, leading to an efficient bandwidth usage. This is confirmed with preliminary experimental results obtained on an FTT-CAN network}
}
@inproceedings{BEHNAM_ETFA_2011,
author = {Behnam, M. and Marau, R. and Pedreiras, P.},
title = {Analysis and optimization of the MTU in real-time communications over Switched Ethernet},
booktitle = {16th Conference on Emerging Technologies Factory Automation (ETFA'2011) Proceedings},
year = {2011},
editor = {},
volume = {},
series = {},
pages = {1--7},
address = {Toulouse, France},
month = {September},
organization = {},
publisher = {},
doi = {10.1109/ETFA.2011.6059021},
issn = {1946-0740},
isbn = {978-1-4577-0016-3},
keywords = {Ethernet, FTT, FTT-SE, protocols, Real-Time communications, Scheduling, MTU},
note = {},
key = {},
abstract = {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}
}
@inproceedings{SANTOS_APRES_2011,
author = {Santos, R. and Pedreiras, P. and Behnam, M. and Nolte, T. and Almeida, L.},
title = {Demonstrating an Ethernet Switch Enhanced with Hierarchical Scheduling},
booktitle = {3rd Workshop on Adaptive and Reconfigurable Embedded Systems (APRES'2011) Proceedings},
year = {2011},
editor = {},
volume = {},
series = {},
pages = {},
address = {Chicago, USA},
month = {April},
organization = {},
publisher = {},
doi = {},
issn = {},
isbn = {},
keywords = {Embedded systems, NES, Ethernet, Switch, FTT, Real-Time communications, Servers, Scheduling, Quality of Service},
note = {},
key = {},
abstract = {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. As response, we developed a multi-level hierarchical server-based architecture for Ethernet switches that provides composability and supports online adaptation and reconfiguration [1] [2]. This framework exhibits the following features: 1) A hierarchical architecture that supports server composition, virtual real-time channels providing temporal isolation (composability in the time domain); 2) Analytical tools for guaranteed real-time behavior; 3) Simple interface to adapt and reconfigure servers during runtime}
}
@article{SANTOS_SIGBED_2011,
author = {Santos, R. and Pedreiras, P. and Behnam, M. and Nolte, T. and Almeida, L.},
title = {Hierarchical server-based traffic scheduling in ethernet switches},
journal = {ACM SIGBED Review},
year = {2011},
volume = {8},
number = {1},
pages = {68--69},
month = {March},
doi = {},
issn = {},
isbn = {},
keywords = {Ethernet, Real-Time communications, Switch, Servers, Quality of Service},
note = {},
key = {},
abstract = {Distributed Embedded Real-Time Systems (DERTS) are ever more complex, consisting of an increasing number of nodes with more functionality and handling more data. This scenario is pushing for paradigm changes in the methodologies to design complex DERTS. Namely, component-oriented design methodologies, exhibiting the composability property are considered an effective means to tackle the growing complexity of DERTS. Server-oriented architectures have proven to be an effective means to enable controlled resource sharing, providing composability among application components as well as between the application software and the hardware platform on which they execute}
}
@article{SILVESTRE_IE_2011,
author = {Silvestre, J. and Almeida, L. and Marau, R. and Pedreiras, P.},
title = {On-line QoS Management for Multimedia Real-Time Transmission in Industrial Networks},
journal = {IEEE Transactions on Industrial Electronics},
year = {2011},
volume = {58},
number = {3},
pages = {1061--1071},
month = {March},
doi = {10.1109/TIE.2010.2049711},
issn = {0278-0046},
isbn = {ISBN-OPTIONAL},
keywords = {Ethernet, Real-Time communications, Industrial Networks, quality of service},
note = {},
key = {},
abstract = {A growing number of industrial applications incorporate multimedia information processing. These multimedia applications are commonly distributed and subject to time constraints that must be met across networks without creating intolerable interference over typical control flows. However, multimedia traffic, in general, and video streaming, in particular, have specific characteristics that conflict with the operational framework of conventional real-time protocols. In particular, video compressors generate highly variable bit-rate streams that mismatch the constant-bit-rate channels typically provided by real-time protocols, severely reducing the efficiency of network utilization. This paper focuses on low-latency multimedia transmission over Ethernet with dynamic quality-of-service (QoS) management. We propose a multidimensional mechanism that controls, in an integrated way, both the compression parameters and the network bandwidth allocated to each stream. The goal is to provide the best possible QoS to each stream, recomputing the compression levels and network bandwidth whenever significant events, such as channel setup/teardown, or structural changes happen. This paper also presents novel QoS metrics based both on the image quality and network parameters. Several experiments with prerecorded video streams illustrate the advantages of the proposed approach and the convenience of the metrics}
}
@inproceedings{SILVA_REC_2011,
author = {Silva, L. and Oliveira, A. and Pedreiras, P. and Santos, R.},
title = {Liga\c{c}\~{a}o de Alto Desempenho entre FPGAs para Switch Ethernet FTT},
booktitle = {VII Jornadas sobre Sistemas Reconfigur\'{a}veis (REC'2011) Proceedings},
year = {2011},
editor = {},
volume = {},
series = {},
pages = {},
address = {Oporto, Portugal},
month = {February},
organization = {},
publisher = {},
doi = {},
issn = {},
isbn = {},
keywords = {FTT, Ethernet, Switch, FPGA, Real-Time communications, HaRTES},
note = {},
key = {},
abstract = {A Ethernet como de?nida na norma IEEE 802.3 n\~{a}o \'{e} adequada a aplica\c{c}\~{o}es tempo-real. Apesar de terem surgido v\'{a}rios protocolos que tornam poss\'{i}vel a sua aplica\c{c}\~{a}o em sistemas de tempo-real, as garantias oferecidas s\~{a}o em geral est\'{a}ticas e pouco ?ex\'{i}veis. O projecto HaRTES tem como objectivo o desenvolvimento de um switch Fast Ethernet com recurso a tecnologia FPGA, capaz de fornecer servic?os de comunica\c{c}\~{a}o tempo-real com garantias din\^{a}micas de qualidade de servi\c{c}o. No entanto, os recursos oferecidos pelas FPGAs e placas de desenvolvimento actuais sao limitados para este tipo de projecto, di?cultando a escalabilidade do switch em diversos aspectos (e.g. numero de portos). O presente artigo discute o desenvolvimento de uma liga\c{c}\~{a}o s\'{e}rie multi-gigabit entre FPGAs que constituem o switch, com vista a minorar as limita\c{c}\~{o}es de escalabilidade no projecto do switch HaRTES}
}
@inproceedings{MARAU_ETFA_2010,
author = {Marau, R. and Almeida, L. and Pedreiras, P. and Lakshmanan, K. and Rajkumar, R.},
title = {Utilization-based schedulability analysis for switched Ethernet aiming dynamic QoS management},
booktitle = {15th IEEE Conference on Emerging Technologies and Factory Automation (ETFA'2010) Proceedings},
year = {2010},
editor = {},
volume = {},
series = {},
pages = {1--10},
address = {Bilbao, Spain},
month = {September},
organization = {},
publisher = {},
doi = {10.1109/ETFA.2010.5641360},
issn = {1946-0740},
isbn = {978-1-4244-6848-5},
keywords = {Ethernet, FTT, FTT-SE, Switch, computational complexity, computer network management, computer network reliability, local area networks, quality of service, routing protocols, scheduling, telecommunication switching},
note = {},
key = {},
abstract = {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}
}
@inproceedings{MARAU_ETFA_2010_2,
author = {Marau, R. and Almeida, L. and Sousa, M. and Pedreiras, P.},
title = {A middleware to support dynamic reconfiguration of real-time networks},
booktitle = {15th IEEE Conference on Emerging Technologies and Factory Automation (ETFA'2010) Proceedings},
year = {2010},
editor = {},
volume = {},
series = {},
pages = {1--10},
address = {Bilbao, Spain},
month = {September},
organization = {},
publisher = {},
doi = {10.1109/ETFA.2010.5641306},
issn = {1946-0740},
isbn = {978-1-4244-6848-5},
keywords = {Middleware, Embedded systems, Distributed embedded systems, Real-Time communications, resource management},
note = {},
key = {},
abstract = {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}
}
@inproceedings{PROCEEDINGS-LABEL,
author = {Santos, R. and Behnam, M. and Nolte, T. and Almeida, L. and Pedreiras, P.},
title = {Schedulability Analysis for Multi-level Hierarchical Server Composition in Ethernet Switches},
booktitle = {9th International Workshop on Real-Time Networks (RTN'2010) Proceedings},
year = {2010},
editor = {},
volume = {},
series = {},
pages = {},
address = {Brussels, Belgium},
month = {July},
organization = {},
publisher = {},
doi = {},
issn = {},
isbn = {},
keywords = {Ethernet, FTT, FTT-SE, Switch},
note = {},
key = {},
abstract = {The FTT-enabled (Flexible Time-Triggered) Ethernet Switch provides flow-based dynamic scheduling that allows to handle bursty traffic in a bandwidth efficient way. For that, this switch uses adaptive resource-reservation, associating servers to flows or groups of flows. This way, flows have a guaranteed, but bounded, access to the communication resources. These servers can take up a compositional multi-level hierarchy and they can be adapted on-line to make a better use of the available bandwidth. To assure a continued real-time behavior, the FTT-enabled Ethernet Switch integrates an admission control mechanism, which screens all adaptation and/or reconfiguration requests. Whenever such requests may compromise the flow timeliness or exceed the available memory, they are rejected. This paper focuses on the flow timeliness verification, only, providing a response-time based schedulability analysis that permits assessing the schedulability of a hierarchical composition of servers and flows}
}
@inproceedings{SANTOS_WFCS_2010,
author = {Santos, R. and Vieira, A. and Pedreiras, P. and Oliveira, A. and Almeida, L. and Marau, R. and Nolte, T.},
title = {Flexible, efficient and robust real-time communication with server-based Ethernet Switching},
booktitle = {8th IEEE International Workshop on Factory Communication Systems (WFCS'2010) Proceedings},
year = {2010},
editor = {},
volume = {},
series = {},
pages = {131--140},
address = {Nancy, France},
month = {May},
organization = {},
publisher = {},
doi = {10.1109/WFCS.2010.5548632},
issn = {},
isbn = {978-1-4244-5462-4},
keywords = {Ethernet, FTT, FTT-SE, Real-Time communications, Switch, Embedded system, Ethernet networks, Protocols, Real time systems, Robustness, Throughput},
note = {},
key = {},
abstract = {The information exchanged in Networked Embedded Systems is steadily increasing in quantity, size, complexity and heterogeneity, with growing requirements for arbitrary arrival patterns and guaranteed QoS. One of the networking protocols that is becoming more common in such systems is Ethernet and its real-time Ethernet variants. However, they hardly support all the referred requirements in an efficient manner since they either favour determinism or throughput, but not both. A potential solution recently proposed by the authors is the Server-SE protocol that uses servers to confine traffic associated to specific applications or subsystems. Such an approach is dynamically reconfigurable and adaptive, being more bandwidth efficient while providing composability in the time domain. This paper proposes integrating the servers inside the Ethernet switch, boosting both the flexibility and the robustness of Server-SE, allowing, for example, the seamless connection of any Ethernet node. The switch is an FTT-enabled Ethernet Switch and the paper discusses two specific ways of integrating the servers, namely in software or in hardware. These options are described and compared analytically and experimentally. The former favours flexibility in the servers design and management while the latter provides lower latency}
}
@inproceedings{SANTOS_WARM_2010,
author = {Santos, R. and Vieira, A. and Marau, R. and Pedreiras, P. and Oliveira, A. and Almeida, L. and Nolte, T.},
title = {Improving the efficiency of Ethernet switches for real-time communication},
booktitle = {1st International Workshop on Adaptive Resource Management (WARM'2010) Proceedings},
year = {2010},
editor = {},
volume = {},
series = {},
pages = {},
address = {Stockholm, Sweden},
month = {April},
organization = {},
publisher = {},
doi = {},
issn = {},
isbn = {},
keywords = {Ethernet, Switch, Real-Time Communications},
note = {},
key = {},
abstract = {}
}
@inproceedings{SANTOS_REC_2010,
author = {Santos, R. and Vieira, A. and Marau, R. and Pedreiras, P. and Oliveira, A. and Almeida, L.},
title = {Architectural Solutions for Server Scheduling Communication within Ethernet Switches},
booktitle = {6th Jornadas sobre Sistemas Reconfigur\'{a}veis (REC'2010) Proceedings},
year = {2010},
editor = {},
volume = {},
series = {},
pages = {},
address = {Aveiro, Portugal},
month = {February},
organization = {},
publisher = {},
doi = {},
issn = {},
isbn = {},
keywords = {Embedded Systems, NES, FTT, Ethernet, Switch, quality of service},
note = {},
key = {},
abstract = {The information exchanged in Network Embedded Systems (NES) is steadily increasing both in terms of quantity, size and complexity. For instance, applications comprising data originated in simple 10 bit ADCs side-by-side with multi-kilobyte variable bit-rate multimedia traffic are, nowadays, becoming a commonplace. Moreover, many NES are frequently subject to some kind of real-time constraints and thus the associated information exchanges are subject to timeliness requirements. However, the existing real-time Ethernet protocols have difficulties in handling these streams efficiently, particularly in what regards the arbitrary arrival patterns and different QoS requirements. To overcome these limitations, the authors proposed recently the integration of server-based traffic scheduling concepts within a customizable Ethernet switch, called FTT-enabled switch. The server scheduling unit can be placed in different points of the FTT-enabled switch architecture. The particular placement chosen has a noticeable impact in terms of server responsiveness, flexibility, hardware complexity and global system schedulability. This paper presents a qualitative comparison about the different architectural solutions and presents a prototype implementation of the hardware-based architecture. Extensive experimental results are also included, showing the correctness of the server operation both in terms of bandwidth guarantees, traffic isolation and latency bounds}
}
@inproceedings{SANTOS_ETFA_2010,
author = {Santos, R. and Pedreiras, P. and Yekeh, F. and Nolte, T. and Almeida, L.},
title = {On hierarchical server-based communication with switched Ethernet},
booktitle = {15th IEEE Conference on Emerging Technologies and Factory Automation (ETFA'2010) Proceedings},
year = {2010},
editor = {},
volume = {},
series = {},
pages = {1--4},
address = {},
month = {},
organization = {},
publisher = {},
doi = {10.1109/ETFA.2010.5641073},
issn = {1946-0740},
isbn = {978-1-4244-6848-5},
keywords = {Ethernet, FTT, FTT-SE, Switch, server-based communication, industrial automation, multiple switches, real-time communications, resource reservation protocol },
note = {},
key = {},
abstract = {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}
}
@inproceedings{SANTOS_CRTS_2009,
author = {Santos, R. and Vieira, A. and Marau, R. and Pedreiras, P. and Oliveira, A. and Almeida, L. and Nolte, T.},
title = {Implementing Server-Based Communication within Ethernet Switches},
booktitle = {2nd Workshop on Compositional Theory and Technology for Real-Time Embedded Systems (CRTS'2009) Proceedings},
year = {2009},
editor = {},
volume = {},
series = {},
pages = {},
address = {Washington, USA},
month = {December},
organization = {},
publisher = {},
doi = {},
issn = {},
isbn = {},
keywords = {Real-Time communications, FTT, FTT-SE, Ethernet, Switch},
note = {},
key = {},
abstract = {Server-based architectures have generated recently a considerable interest. They provide an effective means to support composability, i.e., the integration of diverse components while guaranteeing the required service-levels to each one. While common in CPU scheduling, the support for server-oriented architectures in the domain of real-time communication protocols is more limited due to distribution and specific medium access control and queues management policies within network controllers, network devices and protocol stacks. Consequently, server-based traffic scheduling is either not supported or supported in a limited and inefficient way, e.g., only basic servers, no hierarchical composition, static configuration. To overcome such limitations, the authors proposed recently the Server-SE protocol, which supports unconstrained server-based traffic scheduling over switched Ethernet, using the FTT-SE protocol and common off-the-shelf (COTS) switches as platform. This paper extends such work by bringing the servers inside a customized Ethernet switch. This option provides a high level of determinism, robustness and flexibility, being particularly suited to open systems as servers can easily be added, composed, adapted and removed at run-time. The proposal is validated with a prototype implementation and experimental results that show its effectiveness in enforcing correct resource reservations}
}
@inproceedings{SANTOS_IECON_2009,
author = {Santos, R. and Marau, R. and Vieira, A. and Pedreiras, P. and Oliveira, A. and Almeida, L.},
title = {A synthesizable ethernet switch with enhanced real-time features},
booktitle = {35th Annual Conference of IEEE Industrial Electronics (IECON'2009) Proceedings},
year = {2009},
editor = {},
volume = {},
series = {},
pages = {2817--2824},
address = {Oporto, Portugal},
month = {November},
organization = {},
publisher = {},
doi = {10.1109/IECON.2009.5415405},
issn = {1553-572X},
isbn = {978-1-4244-4650-6},
keywords = {FTT, Ethernet, Real-Time communications, Computer architecture, Ethernet networks, Field programmable gate arrays, Hardware, Protocols, Prototypes, Substation protection, Switches},
note = {},
key = {},
abstract = {The use of switched Ethernet for safe real-time communication still suffers from undesired phenomena, such as blocking caused by long non-preemptive frames, lack of protection against errors in the time domain, couplings across virtual LANs and priority levels via internal switch shared resources. Recently, a few solutions were proposed to cope with such phenomena. One such solution is based on an enhanced switch following the Flexible Time-Triggered paradigm, which enforces strict service differentiation with any kind of traffic scheduling, blocking-free forwarding and timing errors confinement. In this paper we propose a new architecture following an hardware-software co-design approach that simplifies the development of the enhanced switch features by detaching the traffic scheduling from the traffic switching. The paper shows experimental results with an actual switch prototype that confirm the desired switch properties}
}
@inproceedings{SANTOS_REC_2009,
author = {Santos, R. and Marau, R. and Oliveira, A. and Pedreiras, P. and Almeida, L.},
title = {FPGA-based Implementation of an Ethernet Switch for Real-Time Applications},
booktitle = {5th Jornadas sobre Sistemas Reconfigur\'{a}veis (REC'2009) Proceedings},
year = {2009},
editor = {},
volume = {},
series = {},
pages = {},
address = {Monte de Caparica, Portugal},
month = {February},
organization = {},
publisher = {},
doi = {},
issn = {},
isbn = {},
keywords = {Ethernet, Switch, Real-Time communications},
note = {},
key = {},
abstract = {The use of switched Ethernet for precise and safe real-time communication still suffers from undesired phenomena, such as blocking caused by long non-preemptive frames, lack of protection against errors in the time domain, couplings across virtual LANs and priority levels via internal switch shared resources. Recently, a few solutions were proposed to cope with such phenomena. One such solution is based on an enhanced switch following the Flexible Time-Triggered paradigm, which enforces strict service differentiation, blocking-free forwarding and timing errors confinement. In this paper we propose a new architecture following an hardware-software co-design approach that facilitates the development of the enhanced switch features by separating the traffic scheduling from the common management activities associated to switching}
}
@inproceedings{MARAU_CRTS_2008,
author = {Marau, R. and Figueiredo, N. and Santos, R. and Pedreiras, P. and Almeida, L. and Nolte, T.},
title = {Server-based real-time communications on Switched Ethernet},
booktitle = {1st Workshop on Compositional Theory and Technology for Real-Time Embedded Systems (CRTS'2008) Proceedings},
year = {2008},
editor = {},
volume = {},
series = {},
pages = {37--44},
address = {Barcelon, Spain},
month = {November},
organization = {},
publisher = {},
doi = {},
issn = {},
isbn = {},
keywords = {Ethernet, Real-Time communications, FTT, FTT-SE, protocols},
note = {},
key = {},
abstract = {Real-Time Ethernet (RTE) protocols have difficulties in the efficient handling of aperiodic message streams with arbitrary arrival patterns, while at the same time supporting the derivation of timeliness guarantees. This paper presents a server-based mechanism for switched Ethernet real-time networks, integrating concepts from the Server-CAN protocol on the FTT-SE protocol. This approach enables an efficient implementation of arbitrary server schedulers as well as their hierarchical composition. Moreover, the presented approach is very suitable for open systems as servers can easily be added, changed and removed during runtime. The paper includes a case study based on a distributed control application. The obtained results illustrate the correct operation of the server-based protocol, showing the capability of the framework in providing strict timeliness guarantees to the real-time traffic in spite of interference with arbitrary arrival patterns and load variations}
}
@inproceedings{MARAU_ECRTS_2008,
author = {Marau, R. and Almeida, L. and Pedreiras, P. and Nolte, T.},
title = {Towards Server-based Switched Ethernet for Real-Time Communications},
booktitle = {20th Conference on Real-Time Systems (ECRTS'2008) WiP Session Proceedings},
year = {2008},
editor = {},
volume = {},
series = {},
pages = {60--63},
address = {Prague, Czech Republic},
month = {July},
organization = {},
publisher = {},
doi = {},
issn = {},
isbn = {},
keywords = {Ethernet, FTT, FTT-SE, Real-Time communications, Server-CAN, protocols},
note = {},
key = {},
abstract = {This paper presents work-in-progress on server-based Switched Ethernet (SE) for real-time communications. It joins the recent FTT-SE protocol with concepts from the Server-CAN protocol to allow handling aperiodic message streams with arbitrary arrival patterns while supporting the derivation of timeliness guarantees. The presented approach enables an efficient implementation of arbitrary server schedulers in the switch, and a number of server schedulers are to be investigated with respect to SE performance. Moreover, the presented approach is very suitable for open systems as servers can easily be added, changed and removed during runtime of the switch. Currently, several server-based policies are being implemented, which will allow carrying out comparisons among different policies as well as verifying the capability of the protocol for on-line integrated management of the servers}
}
@inproceedings{SANTOS_WFCS_2008,
author = {Santos, R. and Marau, R. and Oliveira, A. and Pedreiras, P. and Almeida, L.},
title = {Designing a costumized Ethernet switch for safe hard real-time communication},
booktitle = {7th IEEE International Workshop on Factory Communication Systems (WFCS'2008) Proceedings},
year = {2008},
editor = {},
volume = {},
series = {},
pages = {169--177},
address = {Dresden, Germany},
month = {May},
organization = {},
publisher = {},
doi = {10.1109/WFCS.2008.4638737},
issn = {},
isbn = {},
keywords = {FPGA, Ethernet, Real-Time communications, FTT, Switch},
note = {},
key = {},
abstract = {The use of switched Ethernet for precise and safe real-time communication still suffers from undesired phenomena that range from the blocking caused by long non-preemptive frames to lack of protection against errors in the time domain and also couplings across virtual LANs and even priority levels via internal switch shared resources. In this paper we propose a novel switch architecture enhanced with resource reservation mechanisms, based on the Flexible Time-Triggered paradigm, which enforces strict service differentiation, blocking-free forwarding and timing errors confinement. Experimental results of a preliminary 4-port prototype based on an FPGA validate the desired properties and exhibit the potential of the enhanced Ethernet switch}
}
@inbook{MARAU_DAES_2007,
author = {Marau, R. and Silva, V. and Ferreira, J. and Almeida, L. and Pedreiras, P. and Martins, E. and Fonseca, J. A.},
title = {Distributed Automotive Embedded Systems},
chapter = {Assessment of FTT-CAN master replication mechanisms for safety-critical applications},
pages = {},
publisher = {SAE International},
year = {2007},
volume = {},
series = {},
type = {},
address = {},
edition = {},
month = {November},
doi = {},
issn = {},
isbn = {978-0-7680-1966-7},
keywords = {FTT, FTT-CAN, CAN, Real-Time communications, protocols, Embedded systems},
note = {},
key = {},
abstract = {The operational flexibility of distributed embedded systems is receiving growing attention because it is required to support on-line adaptation to varying operational conditions, either due to changes in the environment or to faults in the system. However, flexibility makes dependability more difficult to achieve, because there is less a priori knowledge. One protocol that favors flexibility and is widely used in embedded systems, particularly in automotive and robotic systems, is CAN, but some claim that it is not adequate to support safety-critical applications. We argue that CAN, deployed with an adequate overlay protocol, can provide the required support for dependability and flexibility. One such overlying protocol is Flexible Time-Triggered CAN (FTTCAN), that enforces a global notion of time and a global periodic schedule by means of specific messages issued by a master node. In this paper we assess the FTT-CAN master replication mechanisms implemented in a distributed robot control system. Above all, we provide experimental results that show the robustness of such mechanisms}
}
@inproceedings{MARAU_ETFA_2007,
author = {Marau, R. and Almeida, L. and Pedreiras, P. and Harbour, M. and Sangorrin, D. and Medina, J.L.},
title = {Integration of a flexible time triggered network in the FRESCOR resource contracting framework},
booktitle = {12th IEEE Conference on Emerging Technologies and Factory Automation (ETFA'2007) Proceedings},
year = {2007},
editor = {},
volume = {},
series = {},
pages = {1481--1488},
address = {Patras, Greece},
month = {September},
organization = {},
publisher = {},
doi = {10.1109/EFTA.2007.4416964},
issn = {},
isbn = {978-1-4244-0826-9},
keywords = {FRESCOR, Ethernet, FTT, FTT-SE},
note = {},
key = {},
abstract = {In this paper we overview the integration of a framework that generic ally 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}
}
@inproceedings{SILVESTRE_ETFA_2007,
author = {Silvestre, J. and Almeida, L. and Marau, R. and Pedreiras, P.},
title = {Dynamic QoS management for multimedia real-time transmission in industrial environments},
booktitle = {12th IEEE Conference on Emerging Technologies and Factory Automation (ETFA'2007) Proceedings},
year = {2007},
editor = {},
volume = {},
series = {},
pages = {1473--1480},
address = {Patras, Greece},
month = {September},
organization = {},
publisher = {},
doi = {10.1109/EFTA.2007.4416963},
issn = {},
isbn = {978-1-4244-0826-9},
keywords = {FTT-SE, Ethernet, JPEG quantification factor, MJPEG transmission, Bandwidth, Compressors, Condition monitoring, Environmental management, Ethernet, Interference constraints, Machine vision, Protocols, Time factors, Video compression},
note = {},
key = {},
abstract = {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}
}
@inproceedings{ANTUNES_INDIN_2007,
author = {Antunes, A. and Pedreiras, P. and Almeida, L. and Mota, A.},
title = {Dynamic Rate and Control Adaptation in Networked Control Systems},
booktitle = {5th IEEE International Conference on Industrial Informatics (INDIN'2007) Proceedings},
year = {2007},
editor = {},
volume = {2},
series = {},
pages = {841--846},
address = {Vienna, Austria},
month = {July},
organization = {},
publisher = {},
doi = {10.1109/INDIN.2007.4384883},
issn = {1935-4576},
isbn = {978-1-4244-0851-1},
keywords = {Real-Time systems, Embedded systems, distributed control system, distributed feedback control loop system, dynamic rate adaptation technique, embedded control system, networked control system, operational flexibility, sampling period},
note = {},
key = {},
abstract = {Modern embedded control systems are asked to exhibit higher distribution, higher degree of integration and to support operational flexibility. Conventionally the planning of distributed control systems was done either by considering worst-case requirements, leading to expensive and inefficient designs, or by considering average requirements, potentially leading to occasional run-time overloads. The dynamic rate adaptation technique was developed to support operational flexibility and a higher degree of integration in distributed control systems. This technique adapts the communication requirements of distributed feedback control loops by increasing the sampling periods of the messages associated to the control action in order to free network bandwidth when a possible network overload condition is detected. The distributed controllers have to be able to deal with the change of the sampling period and the variable sampling to actuation delay. This work reports different control approaches used in the implementation of the dynamic rate adaptation method, namely a static version based on a set of controllers with parameters pre-computed off-line, a dynamic version where the system parameters are identified online according to the dynamic behaviour of the distributed system and a hybrid version using an adaptive controller with a set of online identifiers}
}
@inproceedings{MARAU_RTN_2007,
author = {Marau, R. and Pedreiras, P. and Almeida, L.},
title = {Asynchronous traffic signaling over master-slave switched ethernet protocols},
booktitle = {6th International Workshop on Real-Time Networks (RTN'2007) Proceedings},
year = {2007},
editor = {},
volume = {},
series = {},
pages = {},
address = {Pisa, Italy},
month = {July},
organization = {},
publisher = {},
doi = {},
issn = {},
isbn = {},
keywords = {Ethernet, FTT, FTT-SE, Real-Time communications, master-slave, protocols },
note = {},
key = {},
abstract = {Network protocol designers have always been divided between the adoption of centralized or distributed communication architectures. Despite exhibiting negative aspects like the existence of a single point-of-failure in the master as well as computational overhead and an inefficient handling of the asynchronous communications, Master-Slave protocols have always found their space mainly given their simplicity of operation and deployment as well as good control over the communication medium. Along the years, many protocols based in this paradigm have been proposed, with many of them being still used today. Some of the negative aspects traditionally exhibited by these protocols have also been attenuated, e.g. with master replication and master/multi-slave control, but the handling of asynchronous requests is still a limitation concerning the response time and overhead. In this paper, we address the specific case of micro-segmented switched Ethernet networks, where Master-Slave protocols are used to control the load submitted to the switch and prevent high queuing jitter and memory overflows. Particularly, we propose a novel signaling mechanism that reduces the asynchronous traffic response time and network overhead, by exploiting the full duplex channels, and analyze the integration of this mechanism in the FTT-SE and Ethernet Powerlink protocols}
}
@inproceedings{MARAU_RTAS_2007,
author = {Marau, R. and Almeida, L. and Pedreiras, P. and Harbour, M. and Sangorrin, D. and Medina, J.L.},
title = {Integration of a flexible network in a resource contracting framework},
booktitle = {13th IEEE Real-Time and Embedded Applications Symposium (RTAS'2007) WiP Session Proceedings},
year = {2007},
editor = {},
volume = {},
series = {},
pages = {},
address = {Bellevue, USA},
month = {April},
organization = {},
publisher = {},
doi = {},
issn = {},
isbn = {},
keywords = {Ethernet, FTT, FTT-SE, FRESCOR, protocols},
note = {},
key = {},
abstract = {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 ?exible 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.}
}
@inbook{ALMEIDA_HRTES_2007,
author = {Almeida, L. and Pedreiras, P. and Ferreira, J. and Calha, J. and Fonseca, J. A. and Marau, R. and Silva, R. and Martins, E.},
title = {Handbook of Real-Time and Embedded Systems},
chapter = {Online QoS Adaptation with the Flexible Time-Triggered (FTT) Communication Paradigm},
pages = {},
publisher = {Chapman and Hall/CRC},
year = {2007},
volume = {},
series = {},
type = {},
address = {},
edition = {},
month = {},
doi = {},
issn = {},
isbn = {978-1-58488-678-5},
keywords = {Ethernet, FTT, FTT-SE, Real-Time communications},
note = {},
key = {},
abstract = {}
}
@inproceedings{ANTUNES_ANIPLA_2006,
author = {Antunes, A. and Pedreiras, P. and Almeida, L. and Mota, A.},
title = {Dynamic Rate Adaptation in Distributed Computer Control Systems},
booktitle = {International Congress of the Italian National Association for Automation (ANIPLA'2006) Proceedings},
year = {2006},
editor = {},
volume = {},
series = {},
pages = {},
address = {Rome, Italy},
month = {November},
organization = {},
publisher = {},
doi = {},
issn = {},
isbn = {},
keywords = {CAN, FTT-CAN, Real-Time, Embedded systems},
note = {Best paper award; selected for journal publication},
key = {},
abstract = {There is currently a trend towards higher distribution in embedded control systems that leads to an increased information exchange among system nodes. Moreover, there are cases in which several subsystems exhibit varying communication requirements. Planning the whole distributed system according to worst-case requirements may lead to expensive and inefficient designs. On the other hand, considering lower requirements may lead to occasional run-time overloads. In this paper we propose a technique based on rate switching to adapt the communication requirements of distributed feedback control loops. This technique reduces the sampling rate of those loops to free network and processor bandwidth and oppose to the overload at the expense of a small degradation of the control quality. The dynamic rate adaptation is carried out using the built-in online scheduling and Quality-of-Service (QoS) management features of the FTT-CAN protocol. The paper includes the description of the approach together with a simulation using TrueTime that shows the effectiveness of the proposed technique}
}
@article{ALMEIDA_MDRMDES_2006,
author = {Almeida, L. and Pedreiras, P. and Marau, R.},
title = {Traffic scheduling anomalies in temporal partitions},
journal = {From Model-driven Design To Resource Management For Distributed Embedded Systems},
year = {2006},
volume = {225},
number = {},
pages = {95--104},
month = {October},
doi = {},
issn = {},
isbn = {978-0-387-39361-2},
keywords = {Real-Time, TDMA},
note = {},
key = {},
abstract = {Many network protocols rely on temporal partitions to provide isolation between different nodes (TDMA slots) or different traffic classes (multi-phase cyclic frameworks). Typically, the duration of the slots or phases is not correlated with the duration of packet transmissions, which is variable and non-preemptive. Thus, it is possible that the limit of the slot or phase be overrun by an on-going packet transmission or, if this cannot be tolerated, idle-time must be inserted at the end of the slot or phase whenever a packet does not fit in. Nevertheless, both situations lead to scheduling anomalies in which the worst-case network delay does not occur necessarily with the synchronous release of all other packets, or just the higher priority ones. This paper highlights two such anomalies showing their origin and indicating that, in such circumstances, it is not possible to determine the worst-case network delay with exactitude in the general case. However, it is still possible to upper bound the network delay and the paper shows non-optimal solutions for those cases}
}
@inproceedings{SANTOS_ETFA_2006,
author = {Santos, F. and Trovao, J. and Marques, A. and Pedreiras, P. and Ferreira, J. and Almeida, L. and Santos, M.},
title = {A Modular Control Architecture for a Small Electric Vehicle},
booktitle = {11th IEEE International Conference on Emerging Technologies and Factory Automation (ETFA'2006) Proceedings},
year = {2006},
editor = {},
volume = {},
series = {},
pages = {139-144},
address = {Prague, Czech Republic},
month = {September},
organization = {},
publisher = {},
doi = {10.1109/ETFA.2006.355456},
issn = {},
isbn = {0-7803-9758-4},
keywords = {CAN, FTT-CAN, accelerate-by-wire safety critical function, brake-by-wire safety critical functions, communication infrastructure, fault-tolerant modular control architecture, small electric vehicle, steer-by-wire safety critical function, x-by-wire subsystems},
note = {},
key = {},
abstract = {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}
}
@inproceedings{MARAU_RTN_2006,
author = {Marau, R. and Almeida, L. and Pedreiras, P.},
title = {Enhanced Ethernet Switching for Flexible Hard Real-Time Communication},
booktitle = {5th International Workshop on Real Time Networks (RTN'2006) Proceedings},
year = {2006},
editor = {},
volume = {},
series = {},
pages = {},
address = {Dresden, Germany},
month = {July},
organization = {},
publisher = {},
doi = {},
issn = {},
isbn = {},
keywords = {FTT, FTT-SE, Ethernet, Real-Time Communication},
note = {},
key = {},
abstract = {Switched Ethernet arose in the last decade as a means to increase global throughput with parallel switching paths, segment the network and create isolated collision domains, thus reducing the non determinism of the original shared Ethernet. However the services provided by COTS Ethernet switches are not enough to guarantee real-time communication, which lead to the development of several switch Ethernet-based protocols, among which the recently proposed FTT-SE. This paper proposes moving the FTT traffic management into the Ethernet switch and discusses how this architectural change enhances the performance of the transmission control and service differentiation mechanisms as well as how error confinement mechanisms can be efficiently deployed. Preliminary experimental results from a prototype implementation validate the services provided by the enhanced Ethernet switch framework}
}
@inproceedings{MARAU_WFCS_2006,
author = {Marau, R. and Almeida, L. and Pedreiras, P.},
title = {Enhancing real-time communication over COTS ethernet switches},
booktitle = {6th IEEE International Workshop on Factory Communication Systems (WFCS'2006) Proceedings},
year = {2006},
editor = {},
volume = {},
series = {},
pages = {295--302 },
address = {Torino, Italy},
month = {June},
organization = {},
publisher = {},
doi = {10.1109/WFCS.2006.1704170},
issn = {},
isbn = {1-4244-0379-0},
keywords = {Ethernet, Real-Time, Communication switching, Delay, Ethernet networks, Job shop scheduling, Multi-access communication, Multicast protocols, Switches, Telecommunication traffic, Throughput, Traffic control},
note = {},
key = {},
abstract = {Switched Ethernet arose in the last decade as a means to increase global throughput with parallel switching paths, segment the network and create isolated collision domains, thus reducing the non determinism of the original shared Ethernet. However, COTS Ethernet switches still suffer from a few drawbacks that affect negatively their real-time communication capabilities. For example, there can be overflows in ports queues with consequences across ports, priority levels and virtual LANs, and the number of priorities is too short for any kind of priority-based scheduling. Moreover, switches present extra latencies and jitter due to the need to interpret frame addresses and also due to different internal architectural solutions. In this paper we propose using the Flexible Time-Triggered communication paradigm to enhance the temporal behavior of Ethernet switches with respect to periodic streams. We explain the system architecture and we present a formulation of the global periodic traffic scheduling problem handled by the FTT master. Simulation and experimental results show the advantages of using such synchronized framework}
}
@article{FERREIRA_II_2006,
author = {Ferreira, J. and Almeida, L. and Fonseca, J. A. and Pedreiras, P. and Martins, E. and Rodriguez-Navas, G. and Rigo, J. and Proenza, J.},
title = {Combining operational flexibility and dependability in FTT-CAN},
journal = {IEEE Transactions on Industrial Informatics},
year = {2006},
volume = {2},
number = {2},
pages = {95--102},
month = {May},
doi = {10.1109/TII.2005.875508},
issn = {1551-3203},
isbn = {},
keywords = {CAN, FTT-CAN, distributed safety-critical systems, dynamic online traffic scheduling, dynamic traffic management, fail-silence enforcement, fault tolerance, flexible time-triggered CAN, master replication, operational dependability, operational flexibility},
note = {},
key = {},
abstract = {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}
}
@inproceedings{ALMEIDA_RTSS_2005,
author = {Almeida, L. and Pedreiras, P.},
title = {Hard Real-Time Communication over COTS Ethernet Switches},
booktitle = {26th IEEE International Real-Time Systems Symposium (RTSS'2005) Work in Progress Session Proceedings},
year = {2005},
editor = {},
volume = {},
series = {},
pages = {},
address = {Miami Florida, USA},
month = {December},
organization = {},
publisher = {},
doi = {},
issn = {},
isbn = {},
keywords = {Ethernet, FTT, FTT-SE},
note = {},
key = {},
abstract = {Switched Ethernet arose in the last decade as a means to increase global throughput with parallel switching paths, segment the network and create isolated collision domains, thus reducing the non-determinism of original shared Ethernet. However, the use of switches, just by itself, is not enough to provide the adequate support to hard real-time communication. For example, there can be overflows in ports queues and the number of priorities is too short for any kind of priority-based scheduling. Moreover, switches present extra latencies and jitter due to the need to interpret frames addresses and also due to different internal architectural solutions. In this paper we propose using the Flexible Time-Triggered communication paradigm to enhance the temporal behavior of Ethernet switches with respect to periodic streams. We explain the system architecture and we present an early formulation of the global periodic traffic scheduling problem that must be handled by the FTT master}
}
@inproceedings{ANTUNES_ETFA_2005,
author = {Antunes, A. and Pedreiras, P. and Mota, A.},
title = {Adapting the sampling period of a real-time adaptive distributed controller to the bus load},
booktitle = {10th IEEE Conference on Emerging Technologies and Factory Automation (ETFA'2005) Proceedings},
year = {2005},
editor = {},
volume = {1},
series = {},
pages = {1084-1088},
address = {Catania, Italy},
month = {September},
organization = {},
publisher = {},
doi = {10.1109/ETFA.2005.1612648},
issn = {},
isbn = {0-7803-9401-1},
keywords = {CAN, FTT-CAN, communication infrastructure, distributed adaptive control system, field bus, message scheduling, network-induced jitter, pole-placement controller, real-time adaptive distributed controller},
note = {},
key = {},
abstract = {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}
}
@inproceedings{SILVA_ETFA_2005,
author = {Silva, V. and Marau, R. and Almeida, L. and Ferreira, J. and Calha, M. and Pedreiras, P. and Fonseca, J. A.},
title = {Implementing a distributed sensing and actuation system: The CAMBADA robots case study},
booktitle = {10th IEEE Conference on Emerging Technologies and Factory Automation (ETFA'2005) Proceedings},
year = {2005},
editor = {},
volume = {2},
series = {},
pages = {781--788},
address = {Catania, Italy},
month = {September},
organization = {},
publisher = {},
doi = {10.1109/ETFA.2005.1612753},
issn = {},
isbn = {0-7803-9401-1},
keywords = {CAN, FTT-CAN, CAMBADA, controller area network, distributed actuation system, distributed computing architecture, distributed embedded system, distributed sensing system, mobile autonomous robotics},
note = {},
key = {},
abstract = {The use of distributed computing architectures has become commonplace in complex embedded systems with potential advantages, for example, in terms of scalability, dependability and maintainability. One particular area in which that trend can be witnessed is mobile autonomous robotics in which several sensors and actuators are interconnected by means of a control network. In this paper we address one case study concerning the CAMBADA robots that were developed at the University of Aveiro for the Robocup Middle Size League. These robots have a distributed architecture with two layers, a coordination layer responsible for the global behaviors and a distributed sensing and actuating layer that conveys internal state information and executes coordination commands. This paper focuses on the latter layer, which is based on the FTT-CAN protocol, following a network-centric approach that provides an efficient framework for the synchronization of all systems activities. We describe the computing and communication requirements, the robot architecture, the system design and implementation, and finally we provide experimental results that show advantages with respect to a non-synchronized distributed approach}
}
@article{PEDREIRAS_II_2005,
author = {Pedreiras, P. and Gai, P. and Almeida, L. and Buttazzo, G.},
title = {FTT-Ethernet: a flexible real-time communication protocol that supports dynamic QoS management on Ethernet-based systems},
journal = {IEEE Transactions on Industrial Informatics},
year = {2005},
volume = {1},
number = {3},
pages = {162--172},
month = {August},
doi = {10.1109/TII.2005.852068},
issn = {1551-3203},
isbn = {},
keywords = {Ethernet, FTT, FTT-Ethernet, distributed systems, dynamic QoS management, manufacturing automation, quality-of-service, real-time communication protocol, real-time industrial automation systems},
note = {},
key = {},
abstract = {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}
}
@inproceedings{FERREIRA_WTR_2005,
author = {Ferreira, J. and Almeida, L. and Fonseca, J. A. and Pedreiras, P. and Santos, M.},
title = {On the dependability and flexibility of CAN and CAN based protocols},
booktitle = {VII Workshop de Tempo Real (WTR'2005) Proceedings},
year = {2005},
editor = {},
volume = {},
series = {},
pages = {},
address = {Fortaleza, Brazil},
month = {May},
organization = {},
publisher = {},
doi = {},
issn = {},
isbn = {},
keywords = {CAN, FTT-CAN, FTT},
note = {},
key = {},
abstract = {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 on-line 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. The paper gathers and reviews the main mechanisms that were developed to provide dependability to the protocol, namely master replication and fail-silence enforcement}
}
@inproceedings{PEDREIRAS_IPDPS_2004,
author = {Pedreiras, P. and Almeida, L.},
title = {Message routing in multi-segment FTT networks: the isochronous approach},
booktitle = {18th International Parallel and Distributed Processing Symposium (IPDPS'2004) Proceedings},
year = {2004},
editor = {},
volume = {3},
series = {},
pages = {122-138},
address = {Santa Fe, New Mexico},
month = {April},
organization = {},
publisher = {},
doi = {10.1109/IPDPS.2004.1303082},
issn = {},
isbn = {0-7695-2132-0},
keywords = {Ethernet, FTT, communication complexity, inter-subsystem communication, isolated network, message routing, multisegment FTT network, protocol, real-time distributed system},
note = {},
key = {},
abstract = {Real-time distributed applications complexity is steadily increasing. A well-known technique used to manage such complexity consists in decomposing the whole system in different quasi-independent distributed subsystems. Inter-subsystem communication, when necessary, is performed via gateway nodes that filter in 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. In the work carried out so far, the FTT communication paradigm has been provided with tools for supporting flexible real-time communication on isolated networks. This work presents a first approach to incorporate multi-segment support into the FTT protocol family. Particularly, 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}
}
@inproceedings{PEDREIRAS_INCOM_2004,
author = {Pedreiras, P. and Almeida, L.},
title = {Minimizing the end-to-end latency in multi-segment time-triggered networks},
booktitle = {11th IFAC Symposium Proceedings on Information Control Problems in Manufacturing 2004 (INCOM'2004)},
year = {2004},
editor = {},
volume = {1},
series = {},
pages = {},
address = {Salvador, Brazil},
month = {April},
organization = {},
publisher = {},
doi = {},
issn = {},
isbn = {},
keywords = {Ethernet, FTT},
note = {},
key = {},
abstract = {Distributed applications complexity is steadily increasing. A well-known technique used to manage such complexity consists in decomposing the whole system in different quasi-independent subsystems, which are also frequently distributed. Inter-subsystem communication, when necessary, is performed via gateway nodes that filter in 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. This work addresses multi-segment time-triggered networks, and, for this class of systems, presents a methodology, which allows minimizing the end-to-end delay for the inter-network traffic. This goal is achieved by bounding the transmission windows of the messages in each one of the intervening networks, and then, taking advantage of the properties of time-triggered systems, making such transmission windows starting as soon as possible. In particular, this is based on the determination of the phase of a message that allows maximizing its best-case response time}
}
@article{FERREIRA_SICICA_2003,
author = {Ferreira, J. and Almeida, L. and Martins, L. and Pedreiras, P.},
title = {Components to enforce fail-silent behaviour in dynamic master-slave systems},
journal = {5th IFAC International Symposium on Intelligent Components and Instruments for Control Applications (SICICA'2003)},
year = {2003},
volume = {},
number = {},
pages = {143--150},
month = {July},
doi = {},
issn = {},
isbn = {},
keywords = {CAN, FTT-CAN, field buses},
note = {},
key = {},
abstract = {This paper considers the case in which master-slave fieldbus networks are used in safety-critical embedded applications, such as transportation systems. Traditional approaches to system design, due to fault-tolerance reasons, have considered static cyclic table-based traffic scheduling, only. However, there is a growing demand for 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 on-line traffic scheduling techniques so that dynamic communication requirements are adequately supported. This paper considers such dynamic master-slave architectures and addresses the problem of enforcing fail silent behavior both in the master and in the slave nodes. Two different mechanisms are proposed, one based on dynamic bus guardians for the slave nodes only, to impose fail silent behavior in the time domain, and other based on internal replication and temporized agreement, to impose fail silence both in the temporal and value domains. Despite being potentially applicable to a set of master-slave networks, this paper discusses the specific implementation of the proposed mechanisms on top of the FTT-CAN protocol}
}
@inproceedings{PEDREIRAS_RTLIA_2003,
author = {Pedreiras, P. and Leite, R. and Almeida, L.},
title = {Characterizing the Real-Time Behavior of Prioritized Switched-Ethernet},
booktitle = {2nd International Workshop on Real-Time LANs in the Internet Age (RTLIA'2003) Proceedings},
year = {2003},
editor = {},
volume = {},
series = {},
pages = {},
address = {Oporto, Portugal},
month = {July},
organization = {},
publisher = {},
doi = {},
issn = {},
isbn = {},
keywords = {Ethernet},
note = {},
key = {},
abstract = {Ethernet is, today, the de facto standard in the Local Area Networks general domain. Despite having been designed for the office environment, it has been appropriately modified or adapted in order to fulfill the requirements of many other fields, including large distributed embedded systems and industrial automation. One typical requirement in such application fields is the need to deliver time-constrained communication services, which cannot be efficiently met using the original CSMA/CD medium access control. Among many possible solutions, either software or hardware-based, the one that became more popular, recently, is the use of switches. However, this does not enforce timeliness per se. In this paper we show a set of practical experiments that reveal the weaknesses of switched Ethernet in what concerns real-time behavior. The results point to the need for further traffic control, at the data sources, if a predictable behavior of the switch is desired}
}
@phdthesis{PEDREIRAS_SFRTCDS_2003,
author = {Pedreiras, P.},
title = {Supporting Flexible Real-Time Communication on Distributed Systems},
school = {University of Aveiro},
year = {2003},
type = {},
address = {Aveiro, Portugal},
month = {June},
note = {},
key = {},
abstract = {Distributed computer-control systems (DCCS) are widely disseminated, appearing in applications ranging from automated process and manufacturing control to automotive, avionics and robotics. Many of these applications comprise real-time activities, that is, activities that must be performed within strict time bounds. Due to its distributed nature, these systems comprise multiple autonomous processing units that, despite being autonomous, need to exchange data in order to achieve control over the environment. For this reason the data exchange among different nodes is also subject to real-time constraints, and thus the communication subsystem must be able to deliver data within specific time bounds.
Many DCCS applications are complex and heterogeneous, comprising different sets of activities with different properties and requirements. For instance, they commonly include periodic activities, e.g. resulting from closed loop control, and sporadic activities resulting from events that occur at unpredictable instants in time in the environment under control. These types of activities can have distinct levels of criticalness and timeliness requirements, independently of their activation nature. On the other hand, flexibility is becoming increasingly important in DCCS, due both to the need of reducing the costs of set-up, configuration changes and maintenance, and also to the recent use of DCCS in new types of applications, such as agile manufacturing, real-time databases with variable number of clients, automotive, mobile robotics in unstructured environments and automatic traffic control systems, that must deal with environments that are inherently dynamic.
To cope with such high degree of complexity and dynamism, distributed real-time systems must support both time and event-triggered communication services under timing constraints and, at the same time, they must be operationally flexible, supporting on-the-fly changes to the computational activities they execute. Concerning specifically the communication subsystem, existing real-time protocols do not generally fulfill these requirements. In systems eminently time-triggered, event-triggered services are either non-existing or handled inefficiently, while in systems eminently event-triggered, interesting properties of time-triggered services are normally lost. On the other hand, flexibility and timeliness are often considered as conflicting: systems that provide timeliness guarantees are based on a static configuration of the communication activities while systems that support dynamic changes to the communication activities do not provide timeliness guarantees}
}
@inproceedings{PEDREIRAS_IPDPS_2003,
author = {Pedreiras, P. and Almeida, L.},
title = {The flexible time-triggered (FTT) paradigm: an approach to QoS management in distributed real-time systems},
booktitle = {17th International Symposium on Parallel and Distributed Processing (IPDPS'2003)},
year = {2003},
editor = {},
volume = {},
series = {},
pages = {},
address = {Nice, France},
month = {April},
organization = {},
publisher = {},
doi = {10.1109/IPDPS.2003.1213243},
issn = {1530-2075},
isbn = {},
keywords = {Ethernet, FTT-Ethernet, message passing, protocols, quality management, quality of service, real-time systems},
note = {},
key = {},
abstract = {Real-time distributed systems are becoming pervasive, supporting a broad range of applications such as avionics, automotive, adaptive control, robotics, computer vision and multimedia. In such systems, several activities are executed on different nodes and cooperate via message passing. One increasingly important concept is that of quality-of-service (QoS), i.e. a system performance metric from the application point-of-view. Concerning the communication system, the QoS delivered to the application is a function of communication parameters such as the rates of message streams. In previous work, the authors have developed two network protocols, FTT-CAN and FTT-Ethernet, which allow online changes to the set of message streams under guaranteed timeliness. The specific network protocols are abstracted away leading to a generic communication paradigm named Flexible Time-Triggered (FTT), which supports online QoS management, with arbitrary policies, in distributed real-time systems. Two possible QoS management policies are referred, priority-based and another one based on the elastic task model, and their use is illustrated with a case study}
}
@article{ALMEIDA_IE_2002,
author = {Almeida, L. and Pedreiras, P. and Fonseca, J. A.},
title = {The FTT-CAN protocol: why and how},
journal = {IEEE Transactions on Industrial Electronics},
year = {2002},
volume = {49},
number = {6},
pages = {1189--1201},
month = {December},
doi = {10.1109/TIE.2002.804967},
issn = {0278-0046},
isbn = {ISBN-OPTIONAL},
keywords = {CAN, FTT-CAN, asynchronous messaging systems, controller area network, fieldbus-based communication systems, flexible operation, flexible time-triggered communication, industrial systems, machine control, manufacturing industry, synchronous messaging systems, timing constraints, controller area networks, distributed control, electronic messaging, field buses, industrial control, protocols, real-time systems},
note = {},
key = {},
abstract = {The requirement for flexible operation is becoming increasingly important in modern industrial systems. This requirement has to be supported at all system levels, including the field level in process industry, as well as the cell and machine control levels in manufacturing industry, where fieldbus-based communication systems are commonly found. Furthermore, typical applications at these levels require both time- and event-triggered communication services, in most cases under stringent timing constraints, to convey state data in the former case and alarms and management data in the latter. However, neither the requirement for flexible operation under guaranteed timeliness nor for joint support of time and event-triggered traffic are efficiently fulfilled by most of existing fieldbus systems. This paper presents a new protocol, flexible time-triggered communication on controller area network, which fulfills both requirements: it supports time-triggered communication in a flexible way as well as being an efficient combination of both time and event-triggered traffic with temporal isolation. These types of traffic are handled by two complementary subsystems, the synchronous and the asynchronous messaging systems, respectively. The paper includes a justification for the new protocol as well as its description and worst case temporal analysis for both subsystems. This analysis shows the capability of the protocol to convey real-time traffic of either type}
}
@inproceedings{FONSECA_AFRICON_2002,
author = {Fonseca, J. A. and Ferreira, J. and Calha, M. and Pedreiras, P. and Almeida, L.},
title = {Issues on task dispatching and master replication in FTT-CAN},
booktitle = {6th IEEE African Electrical Technology Conference Proceedings (AFRICON'2002)},
year = {2002},
editor = {},
volume = {1},
series = {},
pages = {221--226},
address = {George, South Africa},
month = {October},
organization = {},
publisher = {},
doi = {10.1109/AFRCON.2002.1146838},
issn = {},
isbn = {0-7803-7570-X},
keywords = {CAN, FTT-CAN, automotive applications, controller area network, distributed embedded systems, event-triggered traffic, fault tolerance, flexible time-triggered communication, master replication, protocol, task dispatching, temporal isolation},
note = {},
key = {},
abstract = {The FTT-CAN (flexible time-triggered communication on controller area network) protocol supports time-triggered communication in a flexible way as well as the combination of both time and event-triggered traffic with temporal isolation. Previous papers have already discussed its potentialities and presented worst-case temporal analysis for both types of communication. After a brief review of the main characteristics of the protocol, we present new issues concerning its use in distributed embedded systems: the extension for task dispatching and the inclusion of techniques to improve fault tolerance, namely master replication}
}
@article{PEDREIRAS_CCEJ_2002,
author = {Pedreiras, P. and Almeida, L.},
title = {EDF message scheduling on controller area network},
journal = {Computing and Control Engineering Journal},
year = {2002},
volume = {13},
number = {4},
pages = {163--170},
month = {August},
doi = {10.1049/cce:20020402},
issn = {0956-3385},
isbn = {ISBN-OPTIONAL},
keywords = {EDF, CAN, FTT-CAN, flexible time-triggered communication, controller area networks, field buses, earliest deadline first, real-time embedded systems, flexible time-triggered communication, embedded systems},
note = {},
key = {},
abstract = {The controller area network (CAN) has a maximum transmission rate of 1 Mbit/s and its fixed priorities-based medium access control (MAC) limits the maximum bus utilisation when timeliness guarantees are required. An implementation of earliest deadline first (EDF) message scheduling on the CAN, based on the FTT-CAN (flexible time-triggered communication on CAN) protocol, is presented, which allows higher utilisation factors with timeliness guarantees. The advantages of using EDF instead of rate-monotonic scheduling on the FTT-CAN are highlighted, and a comparison with other implementations of EDF scheduling on the CAN is presented}
}
@inproceedings{FERREIRA_WFCS_2002,
author = {Ferreira, J. and Pedreiras, P. and Almeida, L. and Fonseca, J. A.},
title = {Achieving fault tolerance in FTT-CAN},
booktitle = {4th IEEE International Workshop on Factory Communication Systems (WFCS'2002) Proceedings},
year = {2002},
editor = {},
volume = {},
series = {},
pages = {125--132},
address = {V{\"a}ster{\aa}s, Sweden},
month = {August},
organization = {},
publisher = {},
doi = {10.1109/WFCS.2002.1159709},
issn = {},
isbn = {0-7803-7586-6},
keywords = {CAN, FTT-CAN, bus guardians , communication system configuration , fault hypothesis , fault tolerance techniques , flexible time triggered communication over controller area network , master node replication , master synchronization , network errors , node failures , replicated network architecture , safety-critical applications , synchronization , time triggered traffic scheduling},
note = {},
key = {},
abstract = {In order to use the FTT-CAN protocol (flexible time-triggered communication over controller area network) in safety-critical applications, the impact of network errors and node failures must be thoroughly determined and minimized. This paper presents and discusses fault-tolerance techniques to limit that impact. The particular configuration of the communication system can be more or less complex and fault-tolerant as desired by the system designer. The paper includes the fault hypothesis and presents a replicated network architecture using bus guardians. An important aspect is the replication of the master node that schedules the time-triggered traffic. In this case, it is particularly important to assure correct synchronization of the master replicas. The mechanisms that support masters' replication and synchronization are described and their performance is evaluated. The resulting architecture allows a reduction of the conflicts between safety and flexibility, supporting the use of FTT-CAN in safety critical applications}
}
@inproceedings{PEDREIRAS_WFCS_2002,
author = {Pedreiras, P. and Almeida, L. and Gai, P.},
title = {FTT-Ethernet: a platform to implement the Elastic Task Model over message streams},
booktitle = {4th IEEE International Workshop on Factory Communication Systems (WFCS'2002) Proceedings},
year = {2002},
editor = {},
volume = {},
series = {},
pages = {225--232},
address = {V{\"a}ster{\aa}s, Sweden},
month = {August},
organization = {},
publisher = {},
doi = {10.1109/WFCS.2002.1159720},
issn = {},
isbn = {0-7803-7586-6},
keywords = {Ethernet, FTT-Ethernet, Adaptive control , Application software , Automotive engineering , Computer vision , Protocols , Quality of service , Real time systems , Robot vision systems , Streaming media , Vehicle dynamics},
note = {},
key = {},
abstract = {Real-time distributed systems are becoming more pervasive, supporting a broad range of applications such as automotive, adaptive control, robotics, computer vision, and multimedia. Furthermore, in all such applications there is a growing demand for flexibility in order to support dynamic configuration changes such as those arising from evolving requirements and on-line quality-of-service management. The elastic task model, proposed previously, is well suited to support that level of flexibility in multitasking systems running on single processors. This paper presents the extension Of such model to the network, which runs the FTT-Ethernet protocol. The paper includes a brief presentation of this protocol and of the elastic task model, discusses the referred extension and presents a set of experimental results involving the dynamic adjustment of the quality of service delivered to several message streams, with guaranteed timeliness}
}
@article{FERREIRA_MICRO_2002,
author = {Ferreira, J. and Pedreiras, P. and Almeida, L. and Fonseca, J. A.},
title = {The FTT-CAN protocol for flexibility in safety-critical systems},
journal = {IEEE Micro},
year = {2002},
volume = {22},
number = {4},
pages = {46--55},
month = {July/August},
doi = {10.1109/MM.2002.1028475},
issn = {0272-1732},
isbn = {},
keywords = {CAN, FTT-CAN, Time-Triggered Controller Area Network , automotive industry , communication protocol , flexible time-triggered communication on CAN , protocol , safety-critical systems},
note = {},
key = {},
abstract = {A new communication protocol for distributed embedded systems attempts to find a compromise between the often-opposing goals of system flexibility and safety}
}
@inproceedings{PEDREIRAS_ECRTS_2002,
author = {Pedreiras, P. and Almeida, L. and Gai, P.},
title = {The FTT-ethernet protocol: merging flexibility, timeliness and efficiency},
booktitle = {14th Euromicro Conference on Real-Time Systems (ECRTS'2002) Proceedings},
year = {2002},
editor = {},
volume = {},
series = {},
pages = {134--142},
address = {Vienna, Austria},
month = {June},
organization = {},
publisher = {},
doi = {10.1109/EMRTS.2002.1019195},
issn = {1068-3070},
isbn = {},
keywords = {Ethernet, FTT-Ethernet, Application software, Bandwidth, Control systems, Electrical equipment industry, Ethernet networks, Protocols, Real time systems},
note = {},
key = {},
abstract = {Despite having been designed to interconnect office equipment such as computers and printers, since its early days Ethernet 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-time behaviour. 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 hardreal-time operation in a flexible way}
}
@inproceedings{PEDREIRAS_RTLIA_2002,
author = {Pedreiras, P. and Almeida, L.},
title = {Flexibility, timeliness and efficiency over Ethernet},
booktitle = {1st International Workshop on Real-Time LANs in the Internet Age (RTLIA'2002) Proceedings},
year = {2002},
editor = {},
volume = {},
series = {},
pages = {53--56},
address = {Vienna, Austria},
month = {June},
organization = {},
publisher = {},
doi = {},
issn = {},
isbn = {},
keywords = {Ethernet, FTT-Ethernet, Application software, Bandwidth, Control systems, Electrical equipment industry, Ethernet networks, Protocols, Real time systems},
note = {},
key = {},
abstract = {This paper summarises the materials presented in [11] concerning the quest for real-time behaviour over Ethernet and the new protocol FTT-Ethernet. This paper then includes a discussion on the use of this new protocol on networks based on switches, as this is becoming the main architectural choice in LANs}
}
@inproceedings{PEDREIRAS_RTS_2002,
author = {Pedreiras, P. and Almeida, L.},
title = {Flexible Scheduling on Controller Area Network},
booktitle = {10th International Conference on Real-Time Systems (RTS'2002) Proceedings},
year = {2002},
editor = {},
volume = {},
series = {},
pages = {},
address = {Paris, France},
month = {March},
organization = {},
publisher = {},
doi = {},
issn = {},
isbn = {},
keywords = {CAN, FTT-CAN},
note = {},
key = {},
abstract = {The Controller Area Network (CAN) protocol was originally developed aiming at automotive applications. However, it rapidly expanded to other real-time application fields, mainly due to its prioritised medium-access control (MAC), high responsiveness, high data efficiency for short data transfers and low cost. Nevertheless, the fact that its MAC relies on fixed priorities imposes a compromise that, in particular situations, is undesired. For example, CAN does not support fairness among streams of messages that require similar quality-of-service and also, it does not allow very high bandwidth utilization levels with guaranteed timeliness for all message streams. In this paper we briefly present the FTT-CAN protocol (Flexible Time-Triggered communication on CAN) and show how this protocol can be used to efficiently support any type of message scheduling over CAN. Particularly, the paper illustrates this flexibility by focusing on the implementation of Earliest Deadline First (EDF) message scheduling on CAN. A comparison between EDF and Rate Monotonic (RM) scheduling in this environment is performed, namely concerning processing and communication overhead and achievable bus utilization. Schedulability analysis for both RM and EDF is presented, as well as a comparison with other proposals for EDF scheduling on CAN}
}
@inproceedings{PEDREIRAS_RTES_2001,
author = {Pedreiras, P. and Almeida, L.},
title = {A practical approach to EDF scheduling on controller area network},
booktitle = {IEEE/IEE Real-Time Embedded Systems Workshop (RTES'2001) at the 22nd IEEE Real-Time Systems Symposium (RTSS'2001) Proceedings},
year = {2001},
editor = {},
volume = {},
series = {},
pages = {},
address = {London, England},
month = {December},
organization = {},
publisher = {},
doi = {},
issn = {},
isbn = {},
keywords = {CAN, FTT-CAN},
note = {},
key = {},
abstract = {The Controller Area Network (CAN) protocol was originally developed aiming at automotive applications. One of the limitations of this protocol is its maximum transmission rate, specified at 1Mb/s. In practice, the maximum transmission rate can even be lower depending on the desired bus length and available transceiver speed. Furthermore, the message scheduling defined at the medium access control is based on fixed priorities, imposing an even lower limit on the achievable utilisation when timeliness guarantees are required. This paper presents an implementation of Earliest Deadline First (EDF) message scheduling on CAN that allows higher utilisation factors with timeliness guarantees than using fixed priorities. This implementation is based on the FTT-CAN protocol (Flexible Time-Triggered communication on CAN). A comparison between EDF and RM scheduling in this environment is performed, namely concerning processing and communication overhead, bus utilization and network-induced jitter. Schedulability analysis for both RM and EDF is presented as well as a comparison with other proposals for EDF scheduling on CAN}
}
@inproceedings{PEDREIRAS_FET_2001,
author = {Pedreiras, P. and Almeida, L.},
title = {Asynchronous communication on FTT-CAN: Experimental results},
booktitle = {4th IFAC International Conference on Fieldbus Systems and their Applications (FeT'2001) Proceedings},
year = {2001},
editor = {},
volume = {},
series = {},
pages = {113--120},
address = {Nancy, France},
month = {November},
organization = {},
publisher = {INRIA},
doi = {},
issn = {},
isbn = {},
keywords = {CAN, FTT-CAN},
note = {},
key = {},
abstract = {Many real-time control applications require heterogeneous sets of tasks, where both periodic and sporadic computational activities must be performed. For distributed systems, this implies that also the messages that are exchanged at the fieldbus level are heterogeneous in theirs nature. A flexible real-time communication system should, therefore, efficiently support both event triggered and time-triggered communications. The authors have recently proposed a new CAN-based protocol (FTT-CAN) that supports both event-triggered and time-triggered traffic, with temporal isolation. This paper describes the asynchronous messaging system of FTT-CAN, which handles the event-triggered traffic, supporting different QOS requirements. Furthermore, an enhanced response-time analysis concerning this type of traffic and experimental results are also presented}
}
@article{FERREIRA_FET_2001,
author = {Ferreira, J. and Pedreiras, P. and Almeida, L. and Fonseca, J. A.},
title = {FTT CAN Error Confinement},
journal = {4th IFAC International Conference on Fieldbus Systems and their Applications (FeT'2001) Proceedings},
year = {2001},
volume = {},
number = {},
pages = {8--15},
month = {November},
doi = {},
issn = {},
isbn = {},
keywords = {CAN, FFT-CAN},
note = {},
key = {},
abstract = {Transmission errors in a flexible distributed communication system based on the Flexible Time-Triggered Controller Area Network protocol (FTT CAN) must be confined and controlled if such a system is to be used in a safety critical real-time environment. This paper presents a first approach to error confinement in FTT CAN using a deterministic error model. Two strategies to cope with such errors are presented. In the first one the error model is introduced in the schedulability analysis causing the allocation of extra time in each elementary cycle. The second one is based on bus traffic monitoring and on a dynamic scheduler with a schedulability analyzer. The impact of this last strategy on the FTT CAN master node architecture is discussed and a possible solution is presented}
}
@inproceedings{PEDREIRAS_DCCS_2000,
author = {Pedreiras, P. and Almeida, L. and Fonseca, J. A.},
title = {Improving the responsiveness of the synchronous messaging system in FTT-CAN},
booktitle = {16th IFAC Workshop on Distributed Computer Control Systems (DCCS'2000) Proceedings},
year = {2000},
editor = {},
volume = {},
series = {},
pages = {},
address = {Sydney, Australia},
month = {December},
organization = {},
publisher = {},
doi = {},
issn = {},
isbn = {},
keywords = {CAN, FTT-CAN},
note = {},
key = {},
abstract = {A flexible distributed real-time communication system must support modifications to the message set which it conveys. These changes can require a degree of responsiveness ranging from a few milliseconds to some seconds. In FTT-CAN protocol, the responsiveness of the synchronous communication system depends on the plan duration, which, in general cannot be set arbitrarily short. This paper presents a method that uses the asynchronous messaging system to temporarily convey the synchronous messages until the synchronous messaging system can handle them. Furthermore, methods to evaluate offline if a set of requests for modifications can be timely handled are presented}
}
@article{PEDREIRAS_RDET_2000,
author = {Pedreiras, P. and Almeida, L. and Fonseca, J. A.},
title = {A Proposal To Improve The Responsiveness Of The Synchronous Messaging System In FTT-CAN},
journal = {Revista do Departamento de Electr\'{o}nica e Telecomunica\c{c}\~{o}es},
year = {2000},
volume = {3},
number = {2},
pages = {},
month = {October},
doi = {},
issn = {},
isbn = {},
keywords = {CAN, FTT-CAN},
note = {},
key = {},
abstract = {For some years there has been a debate opposing event-triggered and time-triggered traffic paradigms in fieldbuses. It has been commonly accepted that both paradigms have advantages and disadvantages and that the former is better suited to sporadic sources of information, e.g. alarms and management functions, as the latter is more suited to periodic streams of information, e.g. sensor data in control loops. However, for certain applications such as flexible real-time systems, a combination of both paradigms is desirable. In these systems, all those types of traffic can be found. To benefit from the advantages of both paradigms it is important to enforce a temporal isolation between event and time triggered traffic. With respect to this combination, current fieldbus systems that support both sorts of traffic either do not enforce temporal isolation or handle the event-triggered traffic in a bandwidth inefficient way. The authors have recently proposed a new CAN-based protocol that supports time-triggered communication in a flexible way (FTT-CAN). One of the interesting features of such protocol is that it allows an efficient combination of both time-triggered and event-triggered traffic with temporal isolation. This paper describes the asynchronous messaging system of FTT-CAN which is responsible for the support of event-triggered traffic. Furthermore, a response time analysis is carried out concerning the handling of asynchronous communication requests}
}
@inproceedings{PEDREIRAS_WFCS_2000,
author = {Pedreiras, P. and Almeida, L.},
title = {Combining event-triggered and time-triggered traffic in FTT-CAN: analysis of the asynchronous messaging system},
booktitle = {3rd IEEE International Workshop on Factory Communication Systems (WFCS'2000) Proceedings},
year = {2000},
editor = {},
volume = {},
series = {},
pages = {67--75},
address = {Porto, Portugal},
month = {September},
organization = {},
publisher = {},
doi = {10.1109/WFCS.2000.882535},
issn = {},
isbn = {0-7803-6500-3},
keywords = {CAN, FTT-CAN, Asynchronous communication , Bandwidth , Communication system control , Delay , Ergonomics, Field buses , Information resources , Phase control , Protocols , Real time systems},
note = {},
key = {},
abstract = {For some years, there has been a debate opposing event-triggered and time-triggered traffic paradigms in fieldbuses. While the former is better suited to sporadic sources of information, the latter is more suited to periodic streams of information. However, for certain applications, such as flexible real-time systems, a combination of both paradigms is desirable. The authors have recently proposed a new controller area network (CAN) based protocol, called FTT CAN (Flexible Time-Triggered communication on CAN), that supports time-triggered communication in a flexible way. It also allows an efficient combination of both time-triggered and event-triggered traffic with temporal isolation. This paper describes the asynchronous messaging system of the FTT-CAN protocol which is responsible for the support of event-triggered traffic. Furthermore, a response time analysis is carried out concerning the handling of asynchronous communication requests}
}
@inproceedings{FONSECA_ICC_2000,
author = {Fonseca, J. A. and Martins, E. and Almeida, L. and Pedreiras, P. and Neves, P.},
title = {Flexible Time-Triggered Protocol for CAN: new scheduling and dispatching solutions},
booktitle = {7th International CAN Conference (ICC'2000) Proceedings},
year = {2000},
editor = {},
volume = {},
series = {},
pages = {},
address = {New Orleans, USA},
month = {June},
organization = {},
publisher = {},
doi = {},
issn = {},
isbn = {},
keywords = {CAN, FTT-CAN},
note = {},
key = {},
abstract = {One of the possibilities to build robust communication systems with respect to their temporal behaviour is to use autonomous control based on the time-triggered paradigm. The FTT-CAN - flexible time-triggered protocol, relies on centralised scheduling but makes use of the CAN native distributed arbitration to reduce communication overhead. There, a planning scheduler is used within a master node to reduce the scheduling run-time overhead. On-line changes to the communication requirements can then be made under guaranteed timeliness. In addition FTT-CAN also allows an efficient combination of both time-triggered and event-triggered traffic with temporal isolation. In this paper, recent evolutions of the initial protocol definition concerning transmission of synchronous and asynchronous messages are presented. These consist in a time division of the elementary transmission window which optimises the available bandwidth for asynchronous messages, keeping the timeliness of synchronous messages without jeopardising their transmission jitter. A novel solution for the planning scheduler is also presented. It consists in an FPGA-based coprocessor which implements the planning scheduler technique without imposing overhead to the arbiter CPU. With it, it is possible to reduce strongly the plan duration thus allowing on-line admission demanded by system elements and, also, to extend the protocol application to high-speed networks}
}