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  • 1.
    Ahlgren, Bengt
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Computer Systems. Swedish Institute of Computer Science.
    Improving Computer Communication Performance by Reducing Memory Bandwidth Consumption1997Doctoral thesis, comprehensive summary (Other academic)
  • 2.
    Bavier, Andy
    et al.
    Princeton University.
    Voigt, Thiemo
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Systems.
    Wawrzoniak, Mike
    Princeton University.
    Peterson, Larry
    Princeton University.
    Gunningberg, Per
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Systems.
    SILK: Scout Paths in the Linux Kernel2001Report (Other academic)
  • 3.
    Björnfot, Lars
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Computer Systems.
    Specification and Implementation of Distributed Real-Time Systems for Embedded Applications1996Doctoral thesis, comprehensive summary (Other academic)
  • 4.
    Carlsson, Leif
    Uppsala University, Humanistisk-samhällsvetenskapliga vetenskapsområdet, Faculty of Social Sciences, Department of Business Studies.
    Framväxten av en intern redovisning i Sverige. 1900-19452001Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    In this thesis, the historical development of cost accounting in Sweden right up to 1945 is examined. The study has been divided into three periods, 1900-1918, 1919-1936 and 1937-1945 and an examination of the relevant literature, mainly contemporary, has been made. To obtain a notion of the situation prevailing in the companies of the time a number of papers written by students at the Stockholm School of Economics have been analysed. These students had visited various firms and written about their cost accounting systems.

    The study has been made with the main purpose of giving an account of how cost accounting has developed from a technical point of view. A systematic survey has been carried out using a working model built around elements of costs, cost centres and cost objectives. Another purpose has been to examine the factors which could have influenced the design of cost accounting systems during the period. Therefore, a review of the earlier development in Sweden, the Anglo-Saxon countries and Germany has proved to be important for understanding the rise of cost accounting in Sweden.

    The development of cost accounting is characterized by the standardization process which went on from 1927 to 1945. This thesis is based on three important standardization proposals, namely that of 1931 regarding terminology, that of 1936 regarding product calculation (full costing) and that of 1945 regarding a normal chart of accounts for industry. Therefore, a theory of standardization is the foundation for this thesis. Institutional theory is referred to as an explanation of how different factors influenced the design of the cost accounting system.

    There are important conclusions to be drawn. Looking at the cost accounting system certain tendencies can be distinguished: A change was made from after-calculation to pre-calculation; normal costing was recommended; full costing prevailed with a strong connection to accounting and there was a striving for the standardization of terminology, calculations and chart of accounts. The influence from Germany was an important driving force during the whole period. Certain individuals have exerted a strong influence on the design of cost accounting systems. The price changes during and after the First World War gave impulses to use current acquisition costs. Education in cost accounting has had an important influence on the development and an interplay between theory and practice has taken place, since the teachers in higher education also often worked in firms in those days. Naturally, standardization itself has played a dominant part in the development of cost accounting in Sweden.

  • 5.
    Carlström, Jakob
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Division of Computer Systems. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Systems.
    Reinforcement learning for admission control and routing2000Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    When a user requests. a connection to another user or a computer in a communications network, a routing algorithm selects a path for transferring the resulting data stream. If all suitable paths are busy, the user request cannot beserved, and is blocked. A routing algorithm that minimizes this blocking probability results in satisfied users, and maximizes the network operator's revenue. In some cases, it may even be advantageous to block a request from one user, to make it possible to serve other users better. This thesis presents improved and partially new algorithms, based on reinforcement learning, which optimize the way a network is shared.

    A main contribution of the thesis is the development of algorithms thatadapt to arrivals of user requests that are correlated over time. These methodsare shown to increase network utilization in cases where the request arrivalprocesses are statistically self-similar. Another main contribution is gainscheduled routing, which reduces the computational cost associated withmaking routing decisions. The thesis also demonstrates how to integrate theconcept of max-min fairness into reinforcement learning routing.

  • 6.
    Daniels, Mats
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Computer Systems. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Systems.
    Asyl/EFSM: a language for specification of protocols and computers1985Licentiate thesis, comprehensive summary (Other academic)
  • 7.
    Gustafsson, Jan
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Division of Computer Systems. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Systems.
    Analyzing execution-time of object-oriented programs using abstract interpretation2000Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    As a result of the industrial deployment of real-time systems, there is an increasing demandfor methods to perform safe and tight calculation of the worst case execution time (WCET) ofprograms. The WCET is a necessary prerequisite for guaranteeing correct timing behaviour ofreal-time systems. WCET calculation means to find the path, often among a huge number ofpaths, that takes the longest time to execute. The calculation is based on path information for theprogram, such as the maximum number of iterations in loops and identification of paths that arenever executed. In most existing WCET analysis methods, this information is given as manual annotations by the programmer.

    In this thesis we present a method which automatically calculates path information for object-oriented real-time programs by static analysis. Thus, the method can be used in automating the WCET analysis, thereby relieving the programmer from the tedious and error-prone manualannotation work.

    The method, which is based on abstract interpretation, generates safe but not necessarily exactpath information. A trade-off between quality and calculation cost has to be made, since findingthe exact information is a complex, often intractable problem for non-trivial programs.

    We show how the general abstract interpretation theory can be used, in a structured way, toapproximate the semantics of an imperative or object-oriented programming language.

    We have chosen to analyze RealTimeTalk (RTT), an object-oriented language based on Smalltalk,and have developed a prototype tool which implements our analysis for a subset of the language,We show that the tool is capable of analyzing programs with a complexity which would makemanual annotation of the program all but trivial.

  • 8.
    Gällmo, Olle
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Computer Systems. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Systems.
    Learning issues in artificial neural networks for ATM traffic control1995Licentiate thesis, comprehensive summary (Other academic)
  • 9.
    Kindahl, Mats
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Computer Systems.
    Verification of Infinite-State Systems: Decision Problems and Efficient Algorithms1999Doctoral thesis, monograph (Other academic)
    Abstract [en]

    This thesis presents methods for the verification of distributed systems with infinite state spaces. We consider several verification problems for lossy channel systems, a class of infinite-state systems consisting of finite-state machines that communicate over unbounded, but lossy, FIFO channels. We also combine partial order techniques with symbolic techniques to improve performance of verification algorithms for infinite state systems.

    We study several implementation relations between lossy channel systems and finite transition systems, and show decidability of the following problems: trace inclusion, trace equivalence, simulation preorder, bisimulation equivalence, weak bisimulation equivalence in both directions, and weak simulation preorder in one direction. We further show that weak simulation preorder in the other direction is undecidable.

    Partial order reduction techniques are utilised to avoid exploring multiple interleavings of independent transitions. Constraint systems are introduced as a symbolic technique to represent (possibly infinite) sets of states. We present general methods for the application of partial order techniques for the verification of constraint systems. The method described is used for checking safety properties using forward or backward reachability analysis. It is based on the use of a—not necessarily symmetric—commutativity relation between operations. In contrast with previously existing approaches to partial order verification, which are based on a symmetric relation on transitions, our method does not require the relation to be symmetric. Partial order verification methods for lossy channel systems and for unsafe (i.e., infinite-state) Petri nets are developed to demonstrate the applicability of this approach.

  • 10.
    Knutsson, Björn
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Division of Computer Systems. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Systems.
    Architectures for application transparent proxies: A study of network enhancing software2001Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Proxies, software deployed inside the network, play a fundamental role in the Internet by providing enhanced functionality to the network. Deployment of proxies is a flexible way of extending the Internet architecture with new services and to cope with problems that were not foreseen at the time the original Internet protocols were defined. The creation of the Internet is an enormous investment in time, effort and money, and proxies allow us to build on the existing infrastructure to enhance its functionality, rather than replace it.

    As the use of proxies increase, so does the problem of proxy configuration and deployment, especially with respect to interference between different proxies. With a limited number of different proxies, this problem can be dealt with manually, or by encoding knowledge of interfering proxies into each proxy. As the number of proxies grow, methods to automatically detect and cope with conflicts must be devised.

    Therefore, proxies need to coordinate with each other. Towards this end, a signalling protocol that can be used to establish and configure a sequence of one or more proxies along an end-to-end flow is proposed. The protocol is realized as an extension of IP, using an IP option, which simplifies its deployment in the Internet.

    In order to facilitate reasoning about coordination, conflicts and deployment of proxies, a model has been developed. The model is based on the concept of regions, also developed in the thesis. Regions are interconnected parts of the network that share a common property, e.g. administrative control or error characteristic. Along with the model, a classification of proxy architectures with respect to how they gather information and deploy proxies is presented. A method based on this model is also proposed.

    We also propose an algorithm for controlling compression to maximize perceived throughput in situations where available bandwidth and CPU power varies. Along with the algorithm, experimental results that show that the algorithm approximates the best non-adaptive choice in a number of situations are presented. This algorithm has been implemented as an end-to-end enhancement.

  • 11.
    Lundqvist, Kristina
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Division of Computer Systems. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Systems.
    Distributed computing and safety critical systems in Ada2000Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    A system architecture for building large distributed real-time systems is presented. By placing the core run-time system (RTS) functionality in a edicatednetwork node, called the controller, distribution of a single Ada 83 program with preservation of the tasking semantics is possible. RTS proxies on the architecture's processing nodes communicate with the controller over a high-speed network. The communication overhead is shown to be acceptable. Thiswork includes the development of an algorithm for task termination intendedfor hardware implementation.

    A model for distributed systems in Ada 95 based on the Linda model ispresented. The implementation treats Linda tuples as typed objects in theirown right. This type safe Linda is adopted as a distributed shared memory forthe implementation of shared passive packages.

    A formal model of a run-time kernel for the Ada 95 Ravenscar subset suitablefor safety critical systems is presented. The kernel and applications are modelledusing timed automata. Both functional and timing properties of the kernelas well as timing properties of the application are verified using the real-time model checker UPPAAL. Guidelines for transforming Ada applications into timed automata are given.

  • 12.
    Nordström, Ernst
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Computer Systems.
    Markov Decision Problems in ATM Traffic Control1998Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    This thesis discusses how to make cost-effective use of the communication resources in the Broadband Integrated Services Digital Network (B-ISDN), which is based on the Asynchronous Transfer Mode (ATM) switching and multiplexing technique.

    The thesis deals with two important functions in ATM traffic control, namely Call Admission Control (CAC) and routing, which affects both the network operator's revenue over time and the users' Quality of Service (QOS) and Grade of Service (GOS). The routing function finds a route, expressed in terms of successive links, with sufficient QOS (e.g. cell loss probability) according to the CACQOS function. The CACGOS function accepts or rejects the call request based on fairness (e.g. call blocking probability) and revenue considerations.

    The CACGOS and routing tasks are modelled a Semi-Markov Decision Problem (SMDP). The SMDP solution gives high resource utilization and ability to control GOS distribution between the call classes. In SMDP routing, the task is to control the state transitions between reward generating states such that the average reward rate is maximized. In order to obtain a solution with feasible computational complexity, the network SMDP is decomposed into a set of link SMDPs. Each link SMDP is solved by either dynamic programming (DP) or reinforcement learning (RL). DP is based on a model of the decision task in terms of the state transition probabilities and expected reward in each state. RL is not based on a model of the decision task. Instead, the optimal policy is found from simulated state transitions, where long-term reward predictions are corrected by temporal difference learning.

    We study aspects such as delayed set up of wide-band calls, link-level integration of guaranteed QOS services and best effort services, and Poisson versus self-similar call arrival processes.

  • 13.
    Pettersson, Paul
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Computer Systems.
    Modelling and Verification of Real-Time Systems Using Timed Automata: Theory and Practice1999Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    During the last decade, model-checking techniques for the verification of timed system have been developed baaed on the theory of timed automata. The practical limitation in applying these techniques to industrial-size systems is the huge amount of time and memory needed to explore and store the state-space of the system model.

    In this thesis, we improve the current status of model-checking techniques for timed systems by developing symbolic, on-the-fly and compositional verification techniques for timed automata. A common characteristics of the model-checking techniques presented is that they use efficient constraint-solving techniques to symbolically represent and manipulate the state-space. To avoid construction of the full state-space of the system model two techniques are used: on-the-fly generation of the state-space and a compositional model-checking technique. The memory-usage is further reduced by developing a minimal and canonical data structure for the class of constraints used in the model-checking algorithm, which reduces the size of each individual state. Two other techniques to reduce the total number of states explored and stored during verification are also presented.

    The developed techniques have been implemented in the verification tool UPPAAL. To demonstrate the potential applications of our model-checking techniques, we present three industrial-size case studies where the UPPAAL tool is applied.

  • 14.
    Sjödin, Mikael
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Division of Computer Systems. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Systems.
    Predictable high-speed communications for distributed real-time systems2000Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The ubiquitous use of computers in modern society is rapidly changing our way of life. In many existing and emerging applications the timely response to events is of utmost importance. Consider for instance a modern vehicle with embedded computers that must react to driver commands within well specified timing tolerances. In designing this and many other type of systems there is a need for methods that can assist in assessing proper functionality and timing. Since many of the involved computers need to communicate with other computers to perform their functions, there is a specific need to analyse communications between computers.

    In particular, methods to calculate the delay of a message sent through a communications network is crucial in the design and validation of distributed hard real-time systems, such as the above mentioned vehicle computer system. The use of such systems is increasing, due to the increased performance and reliability they can offer, as well as the increasing need to control physically distributed equipment. As a consequence, methods to provide timeliness guarantees become more important.

    To assist in providing guarantees of timely delivery of messages, this thesis presents a method to determine the worst case response-time and amount of memory needed for messages sent over Asynchronous Transfer Mode (ATM) networks. An associated priority assignment algorithm, essential for achieving efficient sharing of network resources, is also presented. The methods are intended for admission control of hard real-time traffic, i.e. they can be used to determine if timing requirements will be met or not.

    In a comprehensive evaluation, we compare our method with other methods thatprovide similar guarantees, and show that our response-time analysis enables higher utilisation of network resources compared to the other methods. We show that this success is a result of the high precision in our analysis, combined with the good performance of the priority assignment algorithm.

    In addition, we show the versatility of our method by expanding it to handle more complex traffic patterns which occur in compressed multimedia traffic, and we also present methods improving the efficiency of our analysis.

  • 15.
    Victor, Björn
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Computer Systems.
    The Fusion Calculus: Expressiveness and Symmetry in Mobile Processes1998Doctoral thesis, monograph (Other academic)
    Abstract [en]

    The fusion calculus is presented as a significant step towards a canonical calculus of concurrency. It simplifies and extends the π-calculus of Milner, Parrow and Walker.

    The fusion calculus contains the polyadic π-calculus as a proper subcalculus and thus inherits all its expressive power. In addition fusion contains actions akin to updating a shared state, and a scoping construct for bounding their effects. Therefore it is easier to represent computational models with shared state, including concurrent constraint formalisms. It is also easy to represent the so called strong reduction strategies in the Λ-calculus, involving reduction under abstraction. In the π-calculus thesetasks require elaborate encodings.

    The fusion calculus simplifies the π-calculus by reducing the number of binding operators and the number of bisimulation equivalences, and by making input and output symmetric like in pure CCS. We attain a calculus where concepts from other models of computation are more easily expressed than in the π-calculus, thereby taking a step towards a unified yet simple model of computation.

    In this thesis we present a broad foundational theory of the fusion calculus. We define its labelled and unlabelled operational semantics, and treat strong and weak bisimulation equivalences for both semantics in some detail, including complete axiom systems for finite terms. The equivalences are given symbolic characterisations, leading to algorithms and an automatic tool for equivalence checking. We demonstrate the expressive power of the fusion calculus to give simple encodings of foundational calculi for functional and concurrent constraint programming.

  • 16.
    Voigt, Thiemo
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Division of Computer Systems. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Systems.
    Architectures for Service Differentiation in Overloaded Internet Servers2002Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Web servers become overloaded when one or several server resources such as network interface, CPU and disk become overutilized. Server overload leads to low server throughput and long response times experienced by the clients.

    Traditional server design includes only marginal or no support for overload protection. This thesis presents the design, implementation and evaluation of architectures that provide overload protection and service differentiation in web servers. During server overload not all requests can be processed in a timely manner. Therefore, it is desirable to perform service differentiation, i.e., to service requests that are regarded as more important than others. Since requests that are eventually discarded also consume resources, admission control should be performed as early as possible in the lifetime of a web transaction. Depending on the workload, some server resources can be overutilized while the demand on other resources is low because certain types of requests utilize one resource more than others.

    The implementation of admission control in the kernel of the operating system shows that this approach is more efficient and scalable than implementing the same scheme in user space. We also present an admission control architecture that performs admission control based on the current server resource utilization combined with knowledge about resource consumption of requests. Experiments demonstrate more than 40% higher throughput during overload compared to a standard server and several magnitudes lower response times.

    This thesis also presents novel architectures and implementations of operating system support for predictable service guarantees. The Nemesis operating system provides applications with a guaranteed communication service using the developed TCP/IP implementation and the scheduling of server resources. SILK (Scout in the Linux kernel) is a new networking stack for the Linux operating system that is based on the Scout operating system. Experiments show that SILK enables prioritizing and other forms of service differentiation between network connections while running unmodified Linux applications.

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