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| 2. |
- Böhm, Annette, 1975-, et al.
(author)
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A Fibre-Optic AWG-Based Real-Time Network and Its Applicability to High-Performance Embedded Computing
- 2005
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In: 19th International Parallel and Distributed Processing Symposium. - Piscataway, N.J. : IEEE Press. - 0769523129 ; , s. 133b-133b
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Conference paper (peer-reviewed)abstract
- In this paper, an architecture and a Medium Access Control (MAC) protocol for a multi-wavelength optical communication network, applicable in short range communication systems like System Area Networks (SANs), are proposed. The main focus lies on guaranteed support for hard and soft real-time traffic. The network is based upon a single-hop star topology with an Arrayed Waveguide Grating (AWG) at its center. Traffic scheduling is centralized in one node (residing together with the AWG in a hub), which communicates through a physical control channel. The AWG's property of spatial wavelength reuse and the combination of fixed-tuned and tunable transceivers in the nodes enable simultaneous control and data transmission. A case study with defined real-time communication requirements in the field of Radar Signal Processing (RSP) was carried out and indicates that the proposed system is very suitable for this kind of application.
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| 3. |
- Fan, Xing, 1975-, et al.
(author)
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Efficient Many-to-Many Real-Time Communication Using an Intelligent Ethernet Switch
- 2004
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In: Proceedings of the 7<sup>th</sup> International Symposium on Parallel Architectures, Algorithms and Networks, 2004. - Piscataway, N.J. : IEEE. - 0769521355 ; , s. 280-287
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Conference paper (peer-reviewed)abstract
- This paper presents a solution for efficient many-to-many communication over switched Ethernet. The performance of using an ordinary switch and an intelligent switch is compared, and the results of the analysis based on 100 Mbit/s fast Ethernet show that an intelligent switch used to handle many-to-many communication can give better performance (shorter latency and higher utilization) than an ordinary switch. We also extend the network to serve many-to-many traffic with real-time demands by adding a thin software layer to the intelligent Ethernet switch and the end-nodes. Earliest deadline first (EDF) scheduling is used.
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| 4. |
- Hoang, Hoai, 1976-, et al.
(author)
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Computing the minimum EDF feasible deadline in periodic systems
- 2006
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In: 12th IEEE International Conference on Embedded and Real-Time Computing Systems and Applications, 2006. Proceedings. - Los Alamitos, Calif. : IEEE Press. - 0769526764 ; , s. 125-134
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Conference paper (peer-reviewed)abstract
- In most real-time applications, deadlines are artifices that need to be enforced to meet different performance requirements. For example, in periodic task sets, jitter requirements can be met by assigning suitable relative deadlines and guaranteeing the feasibility of the schedule. This paper presents a method (called minD) for calculating the minimum EDF-feasible deadline of a real-time task. More precisely, given a set of periodic tasks with hard real-time requirements, which is feasible under EDF, the proposed algorithm allows computing the shortest deadline that can be assigned to an arbitrary task in the set, or to a new incoming task (periodic or aperiodic), still preserving the EDF feasibility of the new task set. The algorithm has a pseudo polynomial complexity and handles arbitrary relative deadlines, which can be less than, equal to, or greater than periods.
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| 5. |
- Hoang, Hoai, 1976-
(author)
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Enhancing the Performance of Distributed Real-time Systems
- 2007
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Doctoral thesis (other academic/artistic)abstract
- Advanced embedded systems can consist of many sensors, actuators and processors that are deployed on one or several boards, while having a demand of interacting with each other and sharing resources. Communication between different components usually has strict timing constraints. There is thus a strong need to provide solutions for time critical communication. This thesis focuses on both the support of real-time services over standard switched Ethernet networks and the improvement of systems' real-time characteristics, such as reducing delay and jitter in processors and on communication links.Switched Ethernet has been chosen in this work because of its major advantages in industry; it supports higher bit-rates than most other current LAN (Local Area Network) technologies, including field buses, still at a low cost. We propose using a star network topology with a single Ethernet switch. Each node is connected to a separate port of the switch via a full-duplex link, thereby eliminating collisions. A solid real-time communication protocol for switched Ethernet networks is proposed in the thesis, including a real-time layer between the Ethernet layer and the TCP/IP suite. The network has the capability of supporting both real-time and non real-time traffic and assuring adaptation to the surrounding protocol standards.Most embedded systems work in a dynamic environment, where the precise behavior of the network traffic can usually not be predicted. To support real-time services, we have chosen the Earliest Deadline scheduling algorithm (EDF) because of its optimality, high efficiency and suitability for being used in adaptive schemes. To be able to increase the amount of guaranteed real-time traffic, the notion of Asymmetric Deadline Partitioning Scheme (ADPS) is introduced. ADPS allows distribution of the end-to-end deadline of a message, sent from any source node in the network to any destination node via the switch, into two sub-deadlines, one for each hop according to the load of the physical link that it must traverse.For the EDF scheduling algorithm, the feasibility test is one of the most important techniques that provides us with information about whether or not the real-time traffic can be guaranteed by the network. With the same computational complexity as the feasibility test, a method has been developed to compute the minimum EDF-feasible deadline for a real-time task. The importance of this method in real-time applications lies in that it can be effectively used to reduce the response times of specific control activities or limit their input-output jitter. To allow more flexibility in the control of delay and jitter in real-time systems, a general approach for reducing task deadlines according to the requirements of individual tasks has been developed. The method allows the user to specify a deadline reduction factor for each task in order to better exploit the available slack according to the tasks' actual requirements.
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| 6. |
- Hoang, Hoai, 1976-, et al.
(author)
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Real-time communication for industrial embedded systems using switched Ethernet
- 2006
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In: ARTES - A network for Real-Time research and graduate Education in Sweden 1997-2006. - Uppsala : Uppsala universitet. - 9150618598 ; , s. 417-427
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Book chapter (peer-reviewed)abstract
- This paper focuses on developing and analyzing support for real-time traffic over a switched Ethernet network without any hardware or protocol modifi- cations. Network architecture with full-duplex switched Ethernet and endnodes has been assumed. The switch and the end nodes control the real-time traffic with Earliest Deadline First (EDF) scheduling on the frame level. No modification to the Ethernet standard is needed in the network that supports both real-time and non-real -time TCP/IP communication. The switch is responsible for admission control where feasibility analysis is made for each link between source and destination. All added traffic handling to support real-time communication is positioned in a thin layer (RT layer) added between the Ethernet layer and the TCP/IP suite. This assures adaptation to the surrounding protocol standards. The RT layer manages traffic on the basis of virtual connections, denoted as RT channels, as well as packet level scheduling. RT channels are created between end-nodes prior to any occurrence of real-time traffic. The comparison of two deadline-partitioning schemes, to partition the delay budget over the links for a path, is also presented. While SDPS (Symmetric Deadline Partitioning Scheme) is straightforward to implement, ADPS (Asymmetric Deadline Partitioning Scheme) is devised in order to have a more flexiblefeasibilitytest. ADPSshows promises in removing bottlenecks from links, especially when a master-slave communication is considered as the traffic pattern, and ADPS proves to be a better choice than SDPS.
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| 7. |
- Hoang, Hoai, 1976-
(author)
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Switched Real-Time Ethernet for Industrial Applications
- 2003
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Licentiate thesis (other academic/artistic)abstract
- The research reported in this thesis has been focused on developing and analyzing how to support real-time traffic over a switched Ethernet network without any hardware or protocol modifications. The work has resulted in a proposed systems model, supporting both real-time and non real-time traffic. Currently this model is intended for a one-switch network, with no shared media. All added traffic handling to support real-time communication is positioned in a thin layer (RT layer) added between the Ethernet layer and the TCP/IP suite. This assures adaptation to the surrounding protocol standards. The RT layer manages traffic on the basis of virtual connections, denoted as RT channels, as well as packet level scheduling. RT channels are created between end-nodes prior to any occurrence of real-time traffic. Asymmetric deadline partitioning between the links of the RT channels is also proposed, in order to increase the number of possible RT channels.
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