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The Global ETD Search service is a free service for researchers
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Showing 11 to 19 of 19 (0.063 seconds)Spelling suggestions: "subject:"soft real time"" "subject:"oft real time""
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Transport Services for Soft Real-Time Applications in IP NetworksGrinnemo, Karl-Johan January 2006 (has links)
In recent years, Internet and IP technologies have made inroads into almost every communication market ranging from best-effort services such as email and Web, to soft real-time applications such as VoIP, IPTV, and video. However, providing a transport service over IP that meets the timeliness and availability requirements of soft real-time applications has turned out to be a complex task. Although network solutions such as IntServ, DiffServ, MPLS, and VRRP have been suggested, these solutions many times fail to provide a transport service for soft real-time applications end to end. Additionally, they have so far only been modestly deployed. In light of this, this thesis considers transport protocols for soft real-time applications. Part I of the thesis focuses on the design and analysis of transport protocols for soft real-time multimedia applications with lax deadlines such as image-intensive Web applications. Many of these applications do not need a completely reliable transport service, and to this end Part I studies so-called partially reliable transport protocols, i.e., transport protocols that enable applications to explicitly trade reliability for improved timeliness. Specifically, Part I investigates the feasibility of designing retransmission-based, partially reliable transport protocols that are congestion aware and fair to competing traffic. Two transport protocols are presented in Part I, PRTP and PRTP-ECN, which are both extensions to TCP for partial reliability. Simulations and theoretical analysis suggest that these transport protocols could give a substantial improvement in throughput and jitter as compared to TCP. Additionally, the simulations indicate that PRTP-ECN is TCP friendly and fair against competing congestion-aware traffic such as TCP flows. Part I also presents a taxonomy for retransmission-based, partially reliable transport protocols. Part II of the thesis considers the Stream Control Transmission Protocol (SCTP), which was developed by the IETF to transfer telephony signaling traffic over IP. The main focus of Part II is on evaluating the SCTP failover mechanism. Through extensive experiments, it is suggested that in order to meet the availability requirements of telephony signaling, SCTP has to be configured much more aggressively than is currently recommended by IETF. Furthermore, ways to improve the transport service provided by SCTP, especially with regards to the failover mechanism, are suggested. Part II also studies the effects of Head-of-Line Blocking (HoLB) on SCTP transmission delays. HoLB occurs when packets in one flow block packets in another, independent, flow. The study suggests that the short-term effects of HoLB could be substantial, but that the long-term effects are marginal.
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A System for Using Perceiver Input to Vary the Quality of Generative Multimedia PerformancesJeff, Byron A. 15 September 2005 (has links)
Generative Multimedia (GM) applications are an increasingly popular way to
implement interactive media performances.
Our contributions include creating a metric for evaluating Generative
Multimedia performances, designing a model for accepting perceiver
preferences, and using those preferences to adapt GM performances.
The metric used is imprecision, which is the ratio of the
actual computation time of a GM element to the computation time of a
complete version of that GM element.
By taking a perceiver's
preferences into account when making adaptation decisions, applications
can produce
GM performances that meet soft real-time
and resource constraints while allocating imprecision to the GM elements
the perceiver least cares about.
Compared to other approaches, perceiver-directed imprecision best allocates
impreciseness while minimizing delay.
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Switched Multi-hop Priority Queued Networks-Influence of priority levels on Soft Real-time PerformanceAhmed, Iftikhar, Farooq, Muhammad January 2010 (has links)
In the last few years, the number of real-time applications has increased. These applications are sensitive and require the methods to utilize existing network capacity efficiently to meet performance requirements and achieve the maximum throughput to overcome delay, jitter and packet loss. In such cases, when the network needs to support highly interactive traffic like packet-switched voice, the network congestion is an issue that can lead to various problems. If the level of congestion is high enough, the users may not be able to complete their calls and have existing calls dropped or may experience a variety of delays that make it difficult to participate smooth conversation. In this paper, we investigate the effect of priority levels on soft real-time performance. We use the priority queues to help us manage the congestion, handle the interactive traffic and improve the over all performance of the system. We consider switched multi-hop network with priority queues. All the switches and end-nodes control the real-time traffic with “Earlier Deadline First” scheduling. The performance of the network is characterized in terms of the average delay, the deadline missing ratio and the throughput. We will analyze these parameters with both the bursty traffic and evenly distributed traffic. We will analyze different priority levels and will see how the increase in priority level increases the performance of the soft real-time system.
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Um método de refinamento para desenvolvimento de software embarcado: uma abordagem baseada em UML-RT e especificações formais. / A refinement method for embedded software development: a based UML-RT and formal specification approach.Polido, Marcelo Figueiredo 18 May 2007 (has links)
Neste trabalho é apresentado um método de refinamento para especificações de sistemas embarcados, baseado na linguagem de especificação gráfica UML-RT e na linguagem de especificação formal CSP-OZ. A linguagem UML-RT é utilizada para descrever a arquitetura de sistemas de tempo real distribuídos e esses mapeados para uma especificação formal através de CSP-OZ. A linguagem de especificação formal CSP-OZ é a combinação da linguagem orientada a objetos Object-Z e a algebra de processos CSP, que descreve o comportamento de processos concorrentes. O método de refinamento proposto é baseado na integração de dois métodos: o de bi-simulação, para refinar a parte comportamental da especificação descrita por CSP; e o de equivalência de especificações, para refinar as estruturas de dados descritas por Object-Z, permitindo assim que características de orientação a objetos possam ser utilizadas. Com o método proposto é possível refinar especificações e, conseqüentemente, verificá-las com sua implementação. O desenvolvimento desse método é rigoroso, incluindo a definição formal para um metamodelo da UML-RT. Um exemplo detalhado é apresentado no final deste trabalho. / In this work, a method of refinement of embedded systems specifications based on the graphical specification language UML-RT and the formal specification CSP-OZ is introduced. The UML-RT is used to model real time distributed architecture systems and these are mapped onto formal specifications using CSP-OZ. The CSP-OZ formal specification language is a combination of the state-based object oriented language Object-Z and the CSP process algebra that describes behavioral models of concurrent processes. The rationale of the proposed refinement method is twofold, the use of bisimulation to refine the behavioral part and the specification matching algorithm to refine the state-based part, supporting object-oriented characteristics. Using this result, an equivalence between the specification-matching algorithm and simulation rules is showed. Using the proposed method it is possible to refine CSP-OZ specifications and verify them against their implementations. The development of the proposed refinement method is rigorous, including a formal definition for a UML-RT metamodel. A detailed study case is given at the end of this work.
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Um método de refinamento para desenvolvimento de software embarcado: uma abordagem baseada em UML-RT e especificações formais. / A refinement method for embedded software development: a based UML-RT and formal specification approach.Marcelo Figueiredo Polido 18 May 2007 (has links)
Neste trabalho é apresentado um método de refinamento para especificações de sistemas embarcados, baseado na linguagem de especificação gráfica UML-RT e na linguagem de especificação formal CSP-OZ. A linguagem UML-RT é utilizada para descrever a arquitetura de sistemas de tempo real distribuídos e esses mapeados para uma especificação formal através de CSP-OZ. A linguagem de especificação formal CSP-OZ é a combinação da linguagem orientada a objetos Object-Z e a algebra de processos CSP, que descreve o comportamento de processos concorrentes. O método de refinamento proposto é baseado na integração de dois métodos: o de bi-simulação, para refinar a parte comportamental da especificação descrita por CSP; e o de equivalência de especificações, para refinar as estruturas de dados descritas por Object-Z, permitindo assim que características de orientação a objetos possam ser utilizadas. Com o método proposto é possível refinar especificações e, conseqüentemente, verificá-las com sua implementação. O desenvolvimento desse método é rigoroso, incluindo a definição formal para um metamodelo da UML-RT. Um exemplo detalhado é apresentado no final deste trabalho. / In this work, a method of refinement of embedded systems specifications based on the graphical specification language UML-RT and the formal specification CSP-OZ is introduced. The UML-RT is used to model real time distributed architecture systems and these are mapped onto formal specifications using CSP-OZ. The CSP-OZ formal specification language is a combination of the state-based object oriented language Object-Z and the CSP process algebra that describes behavioral models of concurrent processes. The rationale of the proposed refinement method is twofold, the use of bisimulation to refine the behavioral part and the specification matching algorithm to refine the state-based part, supporting object-oriented characteristics. Using this result, an equivalence between the specification-matching algorithm and simulation rules is showed. Using the proposed method it is possible to refine CSP-OZ specifications and verify them against their implementations. The development of the proposed refinement method is rigorous, including a formal definition for a UML-RT metamodel. A detailed study case is given at the end of this work.
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Practical Real-Time with Look-Ahead Scheduling / Praktikable Echtzeit durch vorausschauende EinplanungRoitzsch, Michael 21 October 2013 (has links) (PDF)
In my dissertation, I present ATLAS — the Auto-Training Look-Ahead Scheduler. ATLAS improves service to applications with regard to two non-functional properties: timeliness and overload detection. Timeliness is an important requirement to ensure user interface responsiveness and the smoothness of multimedia operations. Overload can occur when applications ask for more computation time than the machine can offer. Interactive systems have to handle overload situations dynamically at runtime. ATLAS provides timely service to applications, accessible through an easy-to-use interface. Deadlines specify timing requirements, workload metrics describe jobs. ATLAS employs machine learning to predict job execution times. Deadline misses are detected before they occur, so applications can react early.
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Practical Real-Time with Look-Ahead SchedulingRoitzsch, Michael 19 September 2013 (has links)
In my dissertation, I present ATLAS — the Auto-Training Look-Ahead Scheduler. ATLAS improves service to applications with regard to two non-functional properties: timeliness and overload detection. Timeliness is an important requirement to ensure user interface responsiveness and the smoothness of multimedia operations. Overload can occur when applications ask for more computation time than the machine can offer. Interactive systems have to handle overload situations dynamically at runtime. ATLAS provides timely service to applications, accessible through an easy-to-use interface. Deadlines specify timing requirements, workload metrics describe jobs. ATLAS employs machine learning to predict job execution times. Deadline misses are detected before they occur, so applications can react early.:1 Introduction
2 Anatomy of a Desktop Application
3 Real Simple Real-Time
4 Execution Time Prediction
5 System Scheduler
6 Timely Service
7 The Road Ahead
Bibliography
Index
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| 18 |
Implementation and quantitative analysis of a real-time sound architectureVoigt, Michael 16 April 2009 (has links) (PDF)
Several available free software audio solutions were analyzed, and Jackdmp—a C++ reimplementation of the renowned JACK Audio Connection Kit—was selected as the most appropriate solution for a real-time audio architecture on DROPS. The JACK sound architecture provides the lowest processing latency possible on a desktop computer for a given set of sound card parameters. It reduces the latency jitter caused by software to zero and synchronizes streams at sample accuracy. A real-time admission scheme for JACK clients is proposed. The execution time of different typical JACK clients was analyzed with measurements to validate the assumptions the proposal is based on, but also to gain further knowledge about their timing behavior. The measurements showed that the condition set by Paul Davis—the time to process a client must be a linear function of the buffer size—holds for all tested clients. Jackdmp was ported to DROPS. The developed design of the port and its implementation is documented here. Measurements showed that—although the real-time performance of the Linux kernel is continuously being improved in the mainline and on special external branches—DROPS can provide a signaling latency that is two times lower on average than the values that can be achieved on the same machine running with a low latency patched Linux kernel. Thus, it can be stated that DROPS is well-suited for real-time audio processing and that the pursued path to use it as the foundation of a truly real-time capable audio workstation should be followed. / Wenn man heute digitale Audiotechnik zum Aufnehmen oder Abmischen von Musik oder anderen Audiodaten verwenden möchte, steht man vor der Wahl, entweder auf eine sehr spezialisierte Hardwarelösung zurückzugreifen oder aber sich eines gewöhnlichen Desktopsystems mit entsprechender Audiosoftware zu bedienen. Der Vorteil eines Desktopsystems ist neben seinem deutlich niedrigeren Preis vor allem die Flexibilität. Bezüglich seines Echtzeitverhaltens bietet ein Computer mit einem Standard-Desktop-Betriebssystem aber bei weitem nicht dieselbe Verlässlichkeit einer spezialisierten Hardwarelösung oder analoger Technik. Die Architektur von DROPS --- mit dem echtzeitfähigen Fiasco- Mikrokern auf der einen Seite sowie der Unterstützung von Legacy-Anwendungen durch L4Linux auf der anderen Seite --- birgt die Hoffnung, die Vorteile von den beiden eben beschriebenen Welten auf einem System mit DROPS kombinieren zu können. Die Motivation meiner Arbeit war es, für dieses langfristige Ziel einen ersten Grundstein zu legen. Dazu war es meine Aufgabe, verschiedene Open-Source- Lösungen hinsichtlich ihrer Eignung als Echtzeit-Audioarchitektur für DROPS zu analysieren und die am besten geeignete auf L4Env zu portieren. Meine Wahl fiel dabei auf das in der Linux-Audio-Szene wohlbekannte Jack Audio Connection Kit (JACK). Desweiteren konnte ich in der Arbeit untersuchen, wie sich die JACK Audioarchitektur in ein globales Echtzeit-Scheduling --- z.B. eines von DROPS --- einbetten ließe, und schlage eine generische Methode dafür vor.
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| 19 |
Implementation and quantitative analysis of a real-time sound architectureVoigt, Michael 06 April 2009 (has links)
Several available free software audio solutions were analyzed, and Jackdmp—a C++ reimplementation of the renowned JACK Audio Connection Kit—was selected as the most appropriate solution for a real-time audio architecture on DROPS. The JACK sound architecture provides the lowest processing latency possible on a desktop computer for a given set of sound card parameters. It reduces the latency jitter caused by software to zero and synchronizes streams at sample accuracy. A real-time admission scheme for JACK clients is proposed. The execution time of different typical JACK clients was analyzed with measurements to validate the assumptions the proposal is based on, but also to gain further knowledge about their timing behavior. The measurements showed that the condition set by Paul Davis—the time to process a client must be a linear function of the buffer size—holds for all tested clients. Jackdmp was ported to DROPS. The developed design of the port and its implementation is documented here. Measurements showed that—although the real-time performance of the Linux kernel is continuously being improved in the mainline and on special external branches—DROPS can provide a signaling latency that is two times lower on average than the values that can be achieved on the same machine running with a low latency patched Linux kernel. Thus, it can be stated that DROPS is well-suited for real-time audio processing and that the pursued path to use it as the foundation of a truly real-time capable audio workstation should be followed. / Wenn man heute digitale Audiotechnik zum Aufnehmen oder Abmischen von Musik oder anderen Audiodaten verwenden möchte, steht man vor der Wahl, entweder auf eine sehr spezialisierte Hardwarelösung zurückzugreifen oder aber sich eines gewöhnlichen Desktopsystems mit entsprechender Audiosoftware zu bedienen. Der Vorteil eines Desktopsystems ist neben seinem deutlich niedrigeren Preis vor allem die Flexibilität. Bezüglich seines Echtzeitverhaltens bietet ein Computer mit einem Standard-Desktop-Betriebssystem aber bei weitem nicht dieselbe Verlässlichkeit einer spezialisierten Hardwarelösung oder analoger Technik. Die Architektur von DROPS --- mit dem echtzeitfähigen Fiasco- Mikrokern auf der einen Seite sowie der Unterstützung von Legacy-Anwendungen durch L4Linux auf der anderen Seite --- birgt die Hoffnung, die Vorteile von den beiden eben beschriebenen Welten auf einem System mit DROPS kombinieren zu können. Die Motivation meiner Arbeit war es, für dieses langfristige Ziel einen ersten Grundstein zu legen. Dazu war es meine Aufgabe, verschiedene Open-Source- Lösungen hinsichtlich ihrer Eignung als Echtzeit-Audioarchitektur für DROPS zu analysieren und die am besten geeignete auf L4Env zu portieren. Meine Wahl fiel dabei auf das in der Linux-Audio-Szene wohlbekannte Jack Audio Connection Kit (JACK). Desweiteren konnte ich in der Arbeit untersuchen, wie sich die JACK Audioarchitektur in ein globales Echtzeit-Scheduling --- z.B. eines von DROPS --- einbetten ließe, und schlage eine generische Methode dafür vor.
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