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Enhancing the Performance of Distributed Real-time Systems
Halmstad University, School of Information Technology, Halmstad Embedded and Intelligent Systems Research (EIS).
2007 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

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.

Place, publisher, year, edition, pages
Göteborg: Chalmers university of technology , 2007. , 156 p.
Series
Doktorsavhandlingar vid Chalmers tekniska högskola. Ny serie, ISSN 0346-718X ; 2599
Keyword [en]
Switched Ethernet, Real-Time Communication, EDF scheduling, Reducation of delay and jitter
National Category
Computer Science
Identifiers
URN: urn:nbn:se:hh:diva-1986Libris ID: 10425756Local ID: 2082/2381ISBN: 978-91-7291-918-1 OAI: oai:DiVA.org:hh-1986DiVA: diva2:239204
Public defence
2007-05-14, Wigforssalen, Halmstad, 10:15 (English)
Opponent
Supervisors
Note

Ingår även i serien: Technical report. D / Department of Computer Science and Engineering, Chalmers University of Technology, 1653-1787 ; 28

Available from: 2008-09-29 Created: 2008-09-29 Last updated: 2016-03-31Bibliographically approved
List of papers
1. Switched real-time Ethernet with earliest deadline first scheduling - protocols and traffic handling
Open this publication in new window or tab >>Switched real-time Ethernet with earliest deadline first scheduling - protocols and traffic handling
2002 (English)In: Parallel and Distributed Computing Practices, ISSN 1097-2803, Vol. 5, no 1, 105-115 p.Article in journal (Refereed) Published
Abstract [en]

There is a strong interest of using the cheap and simple Ethernet technology for industrial and embedded systems. This far, however, the lack of real-time services has prevented this change of used network technology. This paper presents enhancements to full-duplex switched Ethernet for the ability of giving throughput and delay guarantees. 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. The switch broadcasts Ethernet frames regularly to clock synchronize the end nodes and to implement flow control for non-real-time traffic. We have characterized the performance of the network in terms of channel acceptance ratio by simulations with different number of nodes connected to the switch.

Place, publisher, year, edition, pages
Commack, N.Y.: Nova Science Publishers, 2002
Keyword
real-time Ethernet
National Category
Computer Engineering
Identifiers
urn:nbn:se:hh:diva-2743 (URN)2082/3145 (Local ID)2082/3145 (Archive number)2082/3145 (OAI)
Available from: 2009-08-12 Created: 2009-08-12 Last updated: 2016-03-31Bibliographically approved
2. Switched real-time Ethernet in industrial applications - deadline partitioning
Open this publication in new window or tab >>Switched real-time Ethernet in industrial applications - deadline partitioning
2003 (English)In: APCC2003: the Ninth Asia-Pacific Conference on Communications : in conjunction with 6th Malaysia International Conference on Communications (MICC03) : 21-24 September, 2003, City Bayview Hotel, Penang, Malaysia / [ed] Mahamod Ismail et al., Piscataway, N.J.: IEEE , 2003, 76-81 p.Conference paper, (Refereed)
Abstract [en]

This paper presents work on a switched Ethernet network extended to allow for periodic real-time traffic, using earliest deadline first (EDF) scheduling. A scheme of asymmetrically dividing deadlines of real-time channels between the in and outgoing links to/from the switch is proposed (ADPS). The scheme is compared with the simpler approach of dividing the deadlines in two (SDPS). The results of several software simulations of setting up RT channels over a full-duplex switched Ethernet network are presented. The simulations show that the ADPS performs better than the SDPS when master-slave communication is assumed over the network.

Place, publisher, year, edition, pages
Piscataway, N.J.: IEEE, 2003
Keyword
Local area networks, Scheduling, Telecommunication channels, Telecommunication switching, Telecommunication traffic, Transport protocols
National Category
Engineering and Technology
Identifiers
urn:nbn:se:hh:diva-396 (URN)10.1109/APCC.2003.1274315 (DOI)000189415600018 ()2082/720 (Local ID)0-7803-8114-9 (ISBN)2082/720 (Archive number)2082/720 (OAI)
Note
©2003 IEEE. Personal use of this material is permitted. However, permission to reprint/republish this material for advertising or promotional purposes or for creating new collective works for resale or redistribution to servers or lists, or to reuse any copyrighted component of this work in other works must be obtained from the IEEE.Available from: 2007-01-12 Created: 2007-01-12 Last updated: 2016-03-31Bibliographically approved
3. Computing the minimum EDF feasible deadline in periodic systems
Open this publication in new window or tab >>Computing the minimum EDF feasible deadline in periodic systems
2006 (English)In: 12th IEEE International Conference on Embedded and Real-Time Computing Systems and Applications, 2006. Proceedings, Los Alamitos, Calif.: IEEE Press, 2006, 125-134 p.Conference paper, (Refereed)
Abstract [en]

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.

Place, publisher, year, edition, pages
Los Alamitos, Calif.: IEEE Press, 2006
Series
IEEE International Conference on Embedded and Real-Time Computing Systems and Applications, ISSN 1533-2306 ; 2006
Keyword
Real-time, Scheduling
National Category
Computer and Information Science
Identifiers
urn:nbn:se:hh:diva-372 (URN)10.1109/RTCSA.2006.22 (DOI)000240851900019 ()2-s2.0-34547275304 (Scopus ID)2082/696 (Local ID)0-7695-2676-4 (ISBN)2082/696 (Archive number)2082/696 (OAI)
Conference
12th IEEE Conference on Embedded and Real-Time Computing Systems and Applications (RTCSA 2006), 16-18 August 2006, Sydney, Australia
Note

©2006 IEEE. Personal use of this material is permitted. However, permission to reprint/republish this material for advertising or promotional purposes or for creating new collective works for resale or redistribution to servers or lists, or to reuse any copyrighted component of this work in other works must be obtained from the IEEE.

Available from: 2007-01-05 Created: 2007-01-05 Last updated: 2016-03-31Bibliographically approved
4. Reducing Delay and Jitter in Software Control Systems
Open this publication in new window or tab >>Reducing Delay and Jitter in Software Control Systems
2007 (English)In: Proceedings of the 15th International Conference on Real-Time and Network Systems: RTNS’07, Vandoeuvre: Institut National Polytechnique de Lorraine , 2007, 173-182 p.Conference paper, (Refereed)
Abstract [en]

Software control systems may be subject to high interference caused by concurrency and resource sharing. Reducing delay and jitter in such systems is crucial for guaranteeing high performance and predictability. In this paper, we present a general approach for reducing delay and jitter by acting on task relative deadlines. The method allows the user to specify a deadline reduction factor for each task to better exploit the available slack according to specific jitter sensitivity. Experimental results confirm the effectiveness and the generality of the proposed approach with respect to other methods available in the literature.

Place, publisher, year, edition, pages
Vandoeuvre: Institut National Polytechnique de Lorraine, 2007
Keyword
Software Control Systems, Reducing jitter, Reducing delay
National Category
Engineering and Technology
Identifiers
urn:nbn:se:hh:diva-1965 (URN)2082/2360 (Local ID)2-905267-53-4 (ISBN)9782905267535 (ISBN)2082/2360 (Archive number)2082/2360 (OAI)
Conference
15th Conference on real-time and networks systems, LORIA, Nancy, France 29-30 March 2007
Available from: 2008-09-26 Created: 2008-09-26 Last updated: 2016-03-31Bibliographically approved

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