Packet scheduling strategies for emerging service models in the internet

Traditional as well as emerging new Internet applications such as video-conferencing and live multimedia broadcasts from Internet TV stations will rely on scheduling algorithms in switches and routers to meet a diversity of service requirements desired from the network. This dissertation focuses on four categories of service requirements that cover the vast majority of current as well as emerging new applications: best-effort service, guaranteed service (delay and bandwidth), controlled load service, and soft real-time service. For each of these service types, we develop novel packet scheduling strategies that achieve better performance and better fairness than existing strategies.Best-effort and guaranteed services: A fair packet scheduler designed for best- effort service can also be employed to achieve bandwidth and delay guarantees. This dissertation proposes a novel fair scheduling algorithm, called Greedy Fair Queueing (GrFQ),that explicitly incorporates the goal of achieving better fairness into the actions of the scheduler. A simplified version of the scheduler is also proposed for easier deployment in real networks. Controlled load service: This dissertation analyzes and defines requirements on packet schedulers serving traffic that request the controlled load service (part of the Integrated Services architecture). We then propose a novel scheduler, called the CL(®) scheduler, which provides service differentiation for aggregated traffic for controlled load service. The proposed scheduler satisfies the defined requirements with a very low processing complexity and without requiring per-flow management. Soft real-time service: We formally define the service requirements of soft real-time applications which have delay constraints but which can tolerate some packet losses. Two novel schedulers of different levels of complexity are proposed. These schedulers achieve better performance (lower overall loss rates) and better fairness than previously known schedulers.We adapt a metric used widely in economics, called the Gini index, to our purpose of evaluating the fairness achieved by our schedulers under real traffic conditions. The Gini index captures the instantaneous fairness achieved at most instants of time as opposed to previously used measures of fairness in the networking literature. Using real video, audio and gateway traffic traces, we show that the proposed schedulers achieve better performance and fairness characteristics than other known schedulers.Ph.D., Electrical Engineering -- Drexel University, 200

Actes de l'Ecole d'Eté Temps Réel 2005 - ETR'2005

Pdf des actes disponible à l'URL http://etr05.loria.fr/Le programme de l'Ecole d'été Temps Réel 2005 est construit autour d'exposés de synthèse donnés par des spécialistes du monde industriel et universitaire qui permettront aux participants de l'ETR, et notamment aux doctorants, de se forger une culture scientifique dans le domaine. Cette quatrième édition est centrée autour des grands thèmes d'importance dans la conception des systèmes temps réel : Langages et techniques de description d'architectures, Validation, test et preuve par des approches déterministes et stochastiques, Ordonnancement et systèmes d'exploitation temps réel, Répartition, réseaux temps réel et qualité de service

The Virtues of Moderation

On a Friday in 2005, the Los Angeles Times launched an experiment: a “wikitorial” on the Iraq War that any of the paper’s readers could edit. By Sunday, the experiment had ended in abject failure: vandals overran it with crude profanity and graphic pornography. The wikitorial took its inspiration and its technology from Wikipedia, but missed something essential about how the “the free encyclopedia that anyone can edit” staves off abuse while maintaining its core commitment to open participation. The difference is moderation: the governance mechanisms that structure participation in a community to facilitate cooperation and prevent abuse. Town meetings have moderators, and so do online communities. A community’s moderators can promote posts or hide them, honor posters or shame them, recruit users or ban them. Their decisions influence what is seen, what is valued, what is said. They create the conditions under which cooperation is possible. This Article provides a novel taxonomy of moderation in online communities. It breaks down the basic verbs of moderation — exclusion, pricing, organizing, and norm-setting — and shows how they help communities walk the tightrope between the chaos of too much freedom and the sterility of too much control. Scholars studying the commons can learn from moderation, and so can policy-makers debating the regulation of online communities

The Virtues of Moderation

TL;DR—On a Friday in 2005, the Los Angeles Times launched an experiment: a “wikitorial” on the Iraq War that any of the paper’s readers could edit. By Sunday, the experiment had ended in abject failure: vandals overran it with crude profanity and graphic pornography. The wikitorial took its inspiration and its technology from Wikipedia, but missed something essential about how the “the free encyclopedia that anyone can edit” staves off abuse while maintaining its core commitment to open participation. The difference is moderation: the governance mechanisms that structure participation in a community to facilitate cooperation and prevent abuse. Town meetings have moderators, and so do online communities. A community’s moderators can promote posts or hide them, honor posters or shame them, recruit users or ban them. Their decisions influence what is seen, what is valued, what is said. They create the conditions under which cooperation is possible. This Article provides a novel taxonomy of moderation in online communities. It breaks down the basic verbs of moderation—exclusion, pricing, organizing, and norm-setting—and shows how they help communities walk the tightrope between the chaos of too much freedom and the sterility of too much control. Scholars studying the commons can learn from moderation, and so can policy-makers debating the regulation of online communities

Qualität und Nutzen - Über den Gebrauch von Zeit-Wert-Funktionen zur Integration qualitäts- und zeit-flexibler Aspekte in einer dynamischen Echtzeit-Einplanungsumgebung

Scheduling methodologies for real-time applications have been of keen interest to diverse research communities for several decades. Depending on the application area, algorithms have been developed that are tailored to specific requirements with respect to both the individual components of which an application is made up and the computational platform on which it is to be executed. Many real-time scheduling algorithms base their decisions solely or partly on timing constraints expressed by deadlines which must be met even under worst-case conditions. The increasing complexity of computing hardware means that worst-case execution time analysis becomes increasingly pessimistic. Scheduling hard real-time computations according to their worst-case execution times (which is common practice) will thus result, on average, in an increasing amount of spare capacity. The main goal of flexible real-time scheduling is to exploit this otherwise wasted capacity. Flexible scheduling schemes have been proposed to increase the ability of a real-time system to adapt to changing requirements and nondeterminism in the application behaviour. These models can be categorised as those whose source of flexibility is the quality of computations and those which are flexible regarding their timing constraints. This work describes a novel model which allows to specify both flexible timing constraints and quality profiles for an application. Furthermore, it demonstrates the applicability of this specification method to real-world examples and suggests a set of feasible scheduling algorithms for the proposed problem class.Einplanungsverfahren für Echtzeitanwendungen stehen seit Jahrzehnten im Interesse verschiedener Forschungsgruppen. Abhängig vom Anwendungsgebiet wurden Algorithmen entwickelt, welche an die spezifischen Anforderungen sowohl hinsichtlich der einzelnen Komponenten, aus welchen eine Anwendung besteht, als auch an die Rechnerplattform, auf der diese ausgeführt werden sollen, angepasst sind. Viele Echtzeit-Einplanungsverfahren gründen ihre Entscheidungen ausschließlich oder teilweise auf Zeitbedingungen, welche auch bei Auftreten maximaler Ausführungszeiten eingehalten werden müssen. Die zunehmende Komplexität von Rechner-Hardware bedeutet, dass die Worst-Case-Analyse in steigendem Maße pessimistisch wird. Die Einplanung harter Echtzeit-Berechnungen anhand ihrer maximalen Ausführungszeiten (was die gängige Praxis darstellt) resultiert daher im Regelfall in einer frei verfügbaren Rechenkapazität in steigender Höhe. Das Hauptziel flexibler Echtzeit-Einplanungsverfahren ist es, diese ansonsten verschwendete Kapazität auszunutzen. Flexible Einplanungsverfahren wurden vorgeschlagen, welche die Fähigkeit eines Echtzeitsystems erhöhen, sich an veränderte Anforderungen und Nichtdeterminismus im Verhalten der Anwendung anzupassen. Diese Modelle können unterteilt werden in solche, deren Quelle der Flexibilität die Qualität der Berechnungen ist, und jene, welche flexibel hinsichtlich ihrer Zeitbedingungen sind. Diese Arbeit beschreibt ein neuartiges Modell, welches es erlaubt, sowohl flexible Zeitbedingungen als auch Qualitätsprofile für eine Anwendung anzugeben. Außerdem demonstriert sie die Anwendbarkeit dieser Spezifikationsmethode auf reale Beispiele und schlägt eine Reihe von Einplanungsalgorithmen für die vorgestellte Problemklasse vor

Characterization of gastric ATPase vesicle transport

The microsomal fraction of both dog and hog gastric mucosa contains a K⁺ activated ATPase. ATP phosphorylates a peptide of c̅ 100,000 Mᵣ in both species, and dephosphorylation is stimulated by K⁺. By a combination of differential and zonal density gradient centrifugation a membrane fraction is produced containing almost exclusively this peptide region. These vesicles, upon the addition of ATP, take up H⁺ and extrude K⁺. The action of ionophores such as nigericin or valinomycin and the uptake of lipid permeable anions such as thiocyanate or anilino-naphthosulfonic acid indicate the lack of a potential difference during transport. Reconstitution of this material into a planar bilayer indicates that ATP activates a K⁺ conductance and hence, in the presence of K⁺ also a low potential difference is observed. These data suggest that this H⁺ pump is non-electrogenic as prepared in the vesicular form. Using an antibody obtained from rabbits immunized with the highly purified membrane fractions, it was demonstrated that this membrane was derived uniquely from gastric parietal cells. Hence, based on the ability of this ATPase to actively transport H⁺, its cellular origin and on the well known K⁺ requirement for acid secretion in amphibia and mammals, it is concluded that this ATPase is a component of the HCl secretory mechanism of gastric mucosa.Paper I Secretion by in Vitro Amphibian Gastric Mucosa. IN: Physiology of Gastric Secretion: NATO Institute, Myren, J., ed, p. 186 -202, Oslo Press, 1968. • Paper II Frog Gastric Mucosal ATPase. Proc. Soc. Exptl. Biol. Med. 119: 1023 -1027, 1965. • Paper III Action of SCN on Rat Liver Mitochondria. Proc. Soc. Exptl. Biol. Med. 133: 456 -459, 1970. • Paper IV Action of Thiocyanate on Gastric Mucosa in Vitro. Biochim. Biophys. Acta 173: 509 -517, 1969. • Paper V Role of ATP and ATPase in Gastric Acid Secretion. IN: Gastric Secretion, (Sachs, G., Heinz, E., Ullrich, K.J., eds), Academic Press, New York, pp. 321 -343, 1972. • Paper VI Properties of ATPase of Gastric Mucosa. V. Preparation of membranes and mitochondria by zonal centrifugation. Biochim. Biophys. Acta 311: 545 -564, 1973. • Paper VII Characterization of Gastric Mucosal Membranes. VI. The presence of channel- forming substances. Biochim. Biophys. Acta 332: 233 -247, 1974. • Paper VIII Characterization of Gastric Mucosal Membranes. Composition of gastric cell membranes and poly - peptide fractionation using ionic and nonionic detergents. Arch. Biochem. Biophys. 161: 456 -471, 1974. • Paper IX Pronase Method for Isolation of Viable Cells From Necturus Gastric Mucosa. Gastroenterology 61: 189 -200, 1971. • Paper X Specific Effect of Acetylsalicylic Acid on Cation Transport of Isolated Gastric Mucosal Cells. Am. J. Physiol. 235: E16 -E21, 1978. • Paper XI Studies on Adenyl Cyclase in Necturus Gastric Mucosa. Arch. Biochem. Biophys. 143: 123 -126, 1971. • Paper XII Adenyl and Guanyl Cyclase in Rabbit Gastric Mucosa. Am. J. Physiol. 225: 1359 -1363, 1973. • Paper XIII Action of Cholinergic Drugs on Necturus Gastric Mucosa. Am. J. Physiol. 210: 1056 -1060, 1970. • Paper XIV Action of Burimamide, a Histamine Antagonist, on Acid Secretion in Vitro. Am. J. Physiol. 226: 898- 902, 1974. • Paper XV Effects of Sodium Removal on Acid Secretion by the Frog Gastric Mucosa. Proc. Soc. Exptl. Biol. Med. 123: 47 -52, 1966. • Paper XVI Ion Transport by Amphibian Antrum in Vitro. I. General Characteristics. Am. J. Physiol. 228: 1188 -1198, 1975. • Paper XVII Quantitation of Conductance Pathways in Antral Gastric Mucosa. J. Gen. Physiology 65: 645 -662, 1975. Paper XVIII Properties of Gastric Antrum. III. Selectivity and modification of shunt conductance. Gastroenterology 72: 72 -77, 1977. • Paper XIX A Molecular Approach to Epithelial Conductance: Gastric Mucosa. Aired Benzon Symp. V. Transport Mechanisms in Epithelia, Munksgaard, Copenhagen, pp. 257 -274, 1973. • Paper XX Conductance Pathways in Epithelial Tissues. Exp. Eye Res. 16: 241 -249, 1973. • Paper XXI Electrical Properties of Isolated Cells of Necturus Gastric Mucosa. Biochim. Biophys. Acta 241: 261 -272, 1971. • Paper XXII Microelectrode Studies of Gastric Mucosa and Isolated Gastric Cells. Symp. Med. Hoechst. IN: Electrophysiology of Epithelial Cells, p. 257 -279, 1971. • Paper XXIII Microelectrode Studies of Fundic Gastric Mucosa: Cellular Coupling and Shunt Conductance. J. Membr. Biol. 19: 105 -128, 1974, • Paper XXIV The Action of Amytal on Frog Gastric Mucosa. Biochim. Biophys. Acta 143: 522 -531, 1967. Paper XXV Metabolism of Dog Gastric Mucosa. I. Nucleotide Levels in Parietal Cells. J. Biol. Chem. 250: 8321 -8329, 1975. • Paper XXVI Metabolism of Dog Gastric Mucosa. Levels of glycolytic citric acid cycle and other intermediates. J. Biol. Chem. 252: 8572 -8581, 1977. • Paper XXVII Redox Involvement in Acid Secretion in the Amphibian Gastric Mucosa. J. Membr. Biol. 35: 189 -204, 1977. • Paper XXVIII REVIEW: H⁺ Transport by a Non-electrogenic Gastric ATPase as a Model for Acid Secretion. Rev. Physiol. Biochem. Pharmac. 79: 133 -167, 1977. • Paper XXIX Characterization of Gastric Mucosal Membranes. VIII. Localization of peptides by iodination and phosphorylation. J. Biol. Chem. 250: 4802 -2809, 1975. • Paper XXX Characterization of Gastric Mucosal Membranes. IX. Fractionation and Purification of K⁺- ATPase containing vesicles by zonal centrifugation and free flow electrophoresis technique. Biochim. Biophys. Acta. 465: 311 -330, 1977. • Paper XXXI A Non -electrogenic H⁺ Pump in Plasma Membranes of Hog Stomach. J. Biol. Chem. 251: 7690 -7698, 1976. • Paper XXXII Proton Transport by Gastric Membrane Vesicles. Biochim. Biophys. Acta 464: 313 -327, 1977. • Paper XXXIII Cation Transport by Gastric H⁺ + K⁺ ATPase. J. Membr. Biol. 32: 361 -381, 1977. • Paper XXXIV Use of l-anilino-8-naphthalene sulfonate as a Probe of Gastric Vesicle Transport. J. Membr. Biol. 32: 301 -318, 1977. • Paper XXXV Reconstitution of a Proton Pump from Gastric Mucosa. J. Membr. Biol. 35: 285 -301, 1977. • Paper XXXVI Metabolic and Membrane Aspects of Gastric H⁺ Transport. Gastroenterology 73: 931 -940, 1977. • Paper XXXVII Tissue and Cell Localization of Hog Gastric Plasma Membrane by Antibody Technique. Proc. Symp. Gastric. Ion Transport, Special Suppl. Acta Physiol. Scand (Obrink, K.J. and Flemstrom,-G., eds) p. 293 -305, 1978. • Paper XXXVIII Transport Parameters of Gastric Vesicles. Proc. Symp. Gastric Ion Transport, Special Suppl. Acta Physiol. Scand. (Obrink, K.J. and Flemstrom, G., eds) p. 409 -426, 1978. • Paper XL Enzymic Modification of Gastric Transport ATPase. IN: Frontiers of Biological Energetics (Dutton, P.L., Leigh, J., Scarpa, A., eds) Academic Press, New York, Vol. 1, p. 545 -554, 1978. • Paper XLI Transport Characteristics of Frog Gastric Membranes Biochim. Biophys. Acta 551: 432 -447, 1979. • Paper XLII Quantitation of Hydrogen Ion and Potential Gradients in Gastric Plasma Membrane Vesicles. Biochemistry 17: 3345 -3353, 1978