We present algorithms for the design of optimal virtual topologies embedded on wide-area wavelength-routed optical networks, The physical network architecture employs wavelength-conversion-enabled wavelength-routing s...
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We present algorithms for the design of optimal virtual topologies embedded on wide-area wavelength-routed optical networks, The physical network architecture employs wavelength-conversion-enabled wavelength-routing switches (WRS) at the routing nodes, which allow the establishment of circuit-switched ah-optical wavelength-division multiplexed (WDM) channels, called lightpaths. We assume packet-based traffic in the network, such that a packet travelling from its source to its destination may have to multihop through one or more such lightpaths, We present an exact integer linear programming (ILP) formulation for the complete virtual topology design, including choice of the constituent lightpaths, routes for these lightpaths, and intensity of packet flows through these lightpaths, By minimizing the average packet hop distance in our objective function and by relaxing the wavelength-continuity constraints (i.e., assuming wavelength converters at all nodes), He demonstrate that the entire optical network design problem can be considerably simplified and made computationally tractable. Although an ILP may take an exponential amount of time to obtain an exact optimal solution, we demonstrate that terminating the optimization within the first few iterations of the branch-and-bound method provides high-quality solutions, We ran experiments using the CPLEX optimization package on the NSFNET topology, a subset of the PACBELL network topology, as well as a third random topology to substantiate this conjecture. Minimizing the average packet hop distance is equivalent to maximizing the total network throughput under balanced flows through the lightpaths. The problem formulation can be used to design a balanced network, such that the utilizations of both transceivers and wavelengths in the network are maximized, thus reducing the cost of the network equipment. We analyze the tradeoffs in budgeting of resources (transceivers and switch sizes) in the optical network, and demonstra
It is proposed that an optimal strategy for executing a join query in a distributed database system may be computed in a time which is bounded by a polynomial function of the number of relations and the size parameter...
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It is proposed that an optimal strategy for executing a join query in a distributed database system may be computed in a time which is bounded by a polynomial function of the number of relations and the size parameters of the network. The solution so unveiled considers both the transmission costs and the processing costs incurred in delivering the required result to the user that issued the query. The query specifies that several relational tables are to be coalesced and presented to the appropriate user. Undertaking this task demands the utilisation of limited system resources, so that a strategy for fulfilling the request that imposes minimal cost to the system should be devised. Both the processor sites, and the communications links that interconnect them, are utilised;an optimal strategy is one that minimises a weighted sum of processing and data transmission costs. An integer linear programming model of this problem was originally proposed in [Ij;however, no suggestion was given as to how this model might be efficiently solved. By extending the earlier analysis, the recursive nature of the join computation is revealed. Further investigations then produce a modified relationship amenable to algorithmic solution;the resultant procedure has polynomial time and space requirements. (C) 1999 Elsevier Science Ltd. All rights reserved.
The paper presents an algorithm to determine a cost minimal yearly working time. Based on a given set of shift schedules a simultaneous selection- and sequencing procedure is performed resulting in a shift sequence th...
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The paper presents an algorithm to determine a cost minimal yearly working time. Based on a given set of shift schedules a simultaneous selection- and sequencing procedure is performed resulting in a shift sequence that optimizes the yearly working time distribution. In contrast to the usual approaches this method takes into account all the complex working time restrictions implied by the shift schedules and all the related cost structures. The influence of some important planning parameters is discussed extensively.
The paper deals with the complexity of the local search, a topic introduced by Johnson, Papadimitriou, and Yannakakis. One consequence of their work, and a recent paper by Schaffer and Yannakakis, is that the local se...
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The paper deals with the complexity of the local search, a topic introduced by Johnson, Papadimitriou, and Yannakakis. One consequence of their work, and a recent paper by Schaffer and Yannakakis, is that the local search does not provide a polynomial-time algorithm for finding locally optimum solutions for several hard combinatorial optimization problems. This motivates us to seek ''easier'' instances for which the local search is polynomial. In particular it has been proved recently by Schaffer and Yannakakis that the max-cut problem with the FLIP neighborhood is polynomial-time local search (PLS) complete, and hence belongs among the most difficult problems in the PLS class. The FLIP neighborhood of a 2-partition is defined by moving a single vertex to the opposite class. Wr prove that, when restricted to cubic graphs, the FLIP local search becomes ''easy'' and finds a local max-cut in O(n(2)) steps. To prove the result, we introduce a class of integer linear programs associated with cubic graphs and provide a combinatorial characterization of their feasibility.
The processing of a join query in a distributed environment exacts the usage of both the network and its computational facilities. A formulation that accounts for both, and felicitously constructed as an integer linea...
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The processing of a join query in a distributed environment exacts the usage of both the network and its computational facilities. A formulation that accounts for both, and felicitously constructed as an integer linear program, is proposed. Information disseminated among the sites of a distributed system is to be amalgamated and presented to a user, in response to his request. From all possible strategies by which this might be achieved, one necessitating the smallest usage of system resources is to be chosen. The data transferal resources of the network are usually presumed to be of greatest significance, and therefore, an optimal strategy is most often defined to be one which minimizes the total transmission cost. One model conforming to this philosophy, appearing in [1), expediently takes the form of a linearintegerprogram, and so forms the basis for further refinement. In the omission of processing costs, the various processor elements of the network are treated homologously;dissimilarities in processing ability are also ignored. By analyzing the nature of join computations at a single processor, the minimal transmission cost model can be hybridized to incorporate the cost of such computations and differences in processing power.
It is proposed that the execution of a chain query in a distributed system can be usefully and appropriately modeled as an integer linear program. In response to a user request, information in the form of relational t...
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It is proposed that the execution of a chain query in a distributed system can be usefully and appropriately modeled as an integer linear program. In response to a user request, information in the form of relational tables scattered across the network is to be combined and made available to the user. The formulation initially attained by considering the behavior of the distributed system in processing such a query is then reduced by removing redundant linear constraints, to produce a model of minimal transmission cost execution. In view of varying properties displayed by the possibly many optima of this problem, further attention is devoted to discriminating between them. By perturbing the objective function, those solutions requiring fewer network transmissions can be favored at the expense of equal-cost, but more complicated, strategies. This includes those strategies that may specify the transmission of a relation around a cycle;when the costs of transmission between sites forming the cycle are zero, such a solution might otherwise be optimal. Many different ways have been devised to solve programs having some number of variables restricted to taking only integer values in some interval, and virtually any of these might be used to solve the join query model. One possible method, using a tree-search approach, is discussed here.
This paper deals with a systematic method for improving reliability of a large system such as a nuclear power plant. In the first step, an assessment table and score sheet are developed for allocating system reliabili...
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This paper deals with a systematic method for improving reliability of a large system such as a nuclear power plant. In the first step, an assessment table and score sheet are developed for allocating system reliability target to each subsystem. Then, important subsystems are pinpointed by comparison between the reliability target and FTA value of each subsystem. In the second step, a combinatorial optimization technique is used for obtaining optimal combination of countermeasures among subsystems which satisfy the reliability target. After this method is discussed in detail, its application to a BWR nuclear power plant is described.
A heuristic approach is presented to solve the Naval Postgraduate School's quarterly scheduling problem for academic courses and final examinations. The current scheduling system is studied and an auto- mated syst...
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A heuristic approach is presented to solve the Naval Postgraduate School's quarterly scheduling problem for academic courses and final examinations. The current scheduling system is studied and an auto- mated system for data collection is developed and implemented. An automated system for the scheduling of final examinations is designed and implemented. Results using real data from one quarter produced feasible solutions to the final examination scheduling problem of 1700 students, 267 courses and 850 sections. The academic course sched- uling heuristic is discussed including an integer linear programming approach to the timetabling and distribution problem of students among segments of the same course. An example with an optimal solution to the single course scheduling problem is presented.
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