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Runtime Monitoring of Timing Constraints in Distributed RealTime Systems
 RealTime Systems
, 1994
"... . Embedded realtime systems often operate under strict timing and dependability constraints. To ensure responsiveness, these systems must be able to provide the expected services in a timely manner even in the presence of faults. In this paper, we describe a runtime environment for monitoring of t ..."
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Cited by 39 (2 self)
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. Embedded realtime systems often operate under strict timing and dependability constraints. To ensure responsiveness, these systems must be able to provide the expected services in a timely manner even in the presence of faults. In this paper, we describe a runtime environment for monitoring of timing constraints in distributed realtime systems. In particular, we focus on the problem of detecting violations of timing assertions in an environment in which the realtime tasks run on multiple processors, and timing constraints can be either interprocessor or intraprocessor constraints. Constraint violations are detected at the earliest possible time by deriving and checking intermediate constraints from the userspecified constraints. If the violations must be detected as early as possible, then the problem of minimizing the number of messages to be exchanged between the processors becomes intractable. We characterize a subclass of timing constraints that occur commonly in distribu...
A Truncated PrimalInfeasible DualFeasible Network Interior Point Method
, 1994
"... . In this paper we introduce the truncated primalinfeasible dualfeasible interior point algorithm for linear programming and describe an implementation of this algorithm for solving the minimum cost network flow problem. In each iteration, the linear system that determines the search direction is ..."
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Cited by 28 (3 self)
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. In this paper we introduce the truncated primalinfeasible dualfeasible interior point algorithm for linear programming and describe an implementation of this algorithm for solving the minimum cost network flow problem. In each iteration, the linear system that determines the search direction is computed inexactly, and the norm of the resulting residual vector is used in the stopping criteria of the iterative solver employed for the solution of the system. In the implementation, a preconditioned conjugate gradient method is used as the iterative solver. The details of the implementation are described and the code, pdnet, is tested on a large set of standard minimum cost network flow test problems. Computational results indicate that the implementation is competitive with stateoftheart network flow codes. Key Words. Interior point method, linear programming, network flows, primalinfeasible dualfeasible, truncated Newton method, conjugate gradient, maximum flow, experimental test...
Use of dynamic trees in a network simplex algorithm for the maximum flow problem
, 1991
"... Goldfarb and Hao (1990) have proposed a pivot rule for the primal network simplex algorithm that will solve a maximum flow problem on an nvertex, marc network in at most nm pivots and O(n²m) time. In this paper we describe how to extend the dynamic tree data structure of Sleator and Tarjan (1983, ..."
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Cited by 21 (5 self)
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Goldfarb and Hao (1990) have proposed a pivot rule for the primal network simplex algorithm that will solve a maximum flow problem on an nvertex, marc network in at most nm pivots and O(n²m) time. In this paper we describe how to extend the dynamic tree data structure of Sleator and Tarjan (1983, 1985) to reduce the running time of this algorithm to O(nm log n). This bound is less than a logarithmic factor larger than those of the fastest known algorithms for the problem. Our extension of dynamic trees is interesting in its own right and may well have additional applications.
Bounds on Average Delays and Queue Size Averages and Variances in InputQueued CellBased Switches
 IN PROC. IEEE INFOCOM
, 2001
"... In this paper we develop a general methodology, mainly based upon Lyapunov functions, to derive bounds on average delays, and on queue size averages and variances of complex systems of queues. We then apply this methodology to inputbuffered, cellbased switch and router architectures. These archite ..."
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Cited by 19 (1 self)
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In this paper we develop a general methodology, mainly based upon Lyapunov functions, to derive bounds on average delays, and on queue size averages and variances of complex systems of queues. We then apply this methodology to inputbuffered, cellbased switch and router architectures. These architectures require a scheduling algorithm to select at each slot a subset of inputbuffered cells which can be transferred towards output ports. Although the stability properties (i.e., the limit throughput) of inputbuffered, cellbased switches was already studied for several classes of scheduling algorithms, no analytical results concerning cell delays or queue sizes are yet available in the technical literature. We concentrate on purely inputbuffered switches that adopt a Maximum Weight Matching scheduling algorithm, that was proved to be the scheduling algorithm providing the best performance. The derived bounds proved to be rather tight, when compared to simulation results.
Packet Scheduling in InputQueued CellBased Switches
 IEEE INFOCOM 2001
, 2001
"... Inputqueued switch architectures play a major role in the design of high performance switches and routers for packet networks. These architectures must be controlled by a scheduling algorithm, which solves contentions in the transfer of data units from inputs to outputs. Several scheduling algorith ..."
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Cited by 18 (2 self)
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Inputqueued switch architectures play a major role in the design of high performance switches and routers for packet networks. These architectures must be controlled by a scheduling algorithm, which solves contentions in the transfer of data units from inputs to outputs. Several scheduling algorithms were proposed in the literature for inputqueued cell switches, operating on fixedsize data units. In this paper we consider the case of packet switches, i.e., devices operating on variablesize data units at their interfaces, but internally operating on cells, and we propose novel extensions of known scheduling algorithms. We prove that the maximum throughput achievable by inputqueued packet switches is identical to that achievable with input and outputqueued cell switches. We show by simulation that, in the case of packet switches, inputqueued architectures may provide performance advantages over outputqueued architectures.
An accelerated Chow and Liu algorithm: fitting tree distributions to highdimensional sparse data
, 1999
"... Chow and Liu [2] introduced an algorithm for fitting a multivariate distribution with a tree (i.e. a density model that assumes that there are only pairwise dependencies between variables) and that the graph of these dependencies is a spanning tree. The original algorithm is quadratic in the dimes ..."
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Cited by 15 (0 self)
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Chow and Liu [2] introduced an algorithm for fitting a multivariate distribution with a tree (i.e. a density model that assumes that there are only pairwise dependencies between variables) and that the graph of these dependencies is a spanning tree. The original algorithm is quadratic in the dimesion of the domain, and linear in the number of data points that define the target distribution P . This paper shows that for sparse, discrete data, fitting a tree distribution can be done in time and memory that is jointly subquadratic in the number of variables and the size of the data set. The new algorithm, called the acCL algorithm, takes advantage of the sparsity of the data to accelerate the computation of pairwise marginals and the sorting of the resulting mutual informations, achieving speed ups of up to 23 orders of magnitude in the experiments. Copyright c # Massachusetts Institute of Technology, 1998 This report describes research done at the Dept. of Electrical Enginee...
On the Throughput Achievable by Isolated and Interconnected InputQueueing Switches under Multiclass Traffic
 in Proc. IEEE INFOCOM 2002,New
, 2002
"... Many recent studies provide an extended investigation of the maximum throughput achievable in InputQueueing (IQ) or CombinedInput andOutputQueueing (CIOQ) packet switches. Some scheduling policies, among which maximum weight matching algorithms, were identified as optimal, in the sense that they ..."
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Cited by 13 (6 self)
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Many recent studies provide an extended investigation of the maximum throughput achievable in InputQueueing (IQ) or CombinedInput andOutputQueueing (CIOQ) packet switches. Some scheduling policies, among which maximum weight matching algorithms, were identified as optimal, in the sense that they were proved to achieve 100% throughput under any admissible singleclass traffic pattern. Most of the results in the literature, however, consider just one switch in isolation, operating on packets belonging to a single traffic class. In this paper we first generalize known results, showing that a wide class of IQ schedulers operating on multiple traffic classes can achieve 100% throughput. In addition, we address the problem of the maximum throughput achievable in a network of interconnected IQ switches loaded by multiclass traffic, and we devise some simple scheduling policies that guarantee 100% throughput when switches are interconnected in a network. Both the Lyapunov function methodology and the fluid models approach are used to obtain our results.
Scheduling NonUniform Traffic In High Speed Packet Switches And Routers
, 1998
"... Until recently, Internet routers and ATM switches were generally built around a central pool of shared memory buffers and a fast, sharedbus backplane. However, limitations in both memory and bus bandwidth have led to the use of input queues and switched backplanes. Input queues relieve the bottlene ..."
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Cited by 11 (0 self)
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Until recently, Internet routers and ATM switches were generally built around a central pool of shared memory buffers and a fast, sharedbus backplane. However, limitations in both memory and bus bandwidth have led to the use of input queues and switched backplanes. Input queues relieve the bottleneck by distributing the memory over each switch input; and a switched backplane allows packet transfers to take place simultaneously. This thesis focuses on the design of switched backplanes with input queues. In particular, we focus on the design of schedulers for switched backplanes. The scheduler decides the order in which packets, or cells, may traverse the backplane. Studies have shown that existing scheduling algorithms are either too complex to operate at high speed or lack the intelligence to perform well over a wide range of traffic patterns. In this thesis, we present two new algorithms that are fast, simple and efficient. Using the methods of Lyapunov, we prove that both algorithms can achieve 100% throughput for all traffic patterns with independent arrivals. We also demonstrate heuristics that can be implemented in fast and relatively simple hardware. Our exploratory design work shows that the heuristics can make a scheduling decision within 1020 nanoseconds when implemented using 0.25 CMOS technology. At this scheduling speed, it is possible to design switches or routers with more than one terabit per second of aggregate bandwidth.
Scalable continuous queries processing by tracking hotspots
, 2006
"... Abstract This paper considers the problem of scalably processing a large number of continuous queries.We propose a flexible framework with novel data structures and algorithms for groupprocessing and indexing continuous queries by exploiting potential overlaps in query predicates. Our approachparti ..."
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Cited by 10 (5 self)
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Abstract This paper considers the problem of scalably processing a large number of continuous queries.We propose a flexible framework with novel data structures and algorithms for groupprocessing and indexing continuous queries by exploiting potential overlaps in query predicates. Our approachpartitions the collection of continuous queries into groups based on the clustering patterns of the query ranges, and then applies specialized processing strategies to those heavilyclustered groups(or hotspots). To maintain the partition dynamically, we present efficient algorithms that maintain a nearly optimal partition in nearly amortized logarithmic time. We show how to use the hotspotsto scalably process large numbers of continuous selectjoin and bandjoin queries, which are much more challenging than simple range selection queries. Experiments demonstrate that this approachcan improve the processing throughput by orders of magnitude. As another application of hotspots, we show how to use them to build a highquality histogram for intervals in linear time.