9352277
An ATM Switch Capacity Allocation Problem
In this paper, we consider a capacity allocation problem arising in the context of deploying asynchronous transfer mode (ATM) networks. Given types of ATM switches, the problem is to find an optimal allocation of capacity such that the total cost of installed switch modules is minimized, while satisfying all traffic demands. We formulate the problem as an integer programming model, which can be conceptualized as a generalized bin packing problem with capacity constraints. We then develop a surrogate constraint technique of the formulation for enhancing the representation of the model. Guided by the tight lower bound of the surrogate relaxation, we devise an effective tabu search heuristic that provides good quality solutions with guaranteed optimality. We present promising computational results that show the viability of the proposed heuristic and lower bounding methods, and that provide insights into implementation for configuring ATM switch in practice.
45657020
Partial convexification cuts for 0-1 mixed-integer programs
Abstract In this research, we propose a new cut generation scheme based on constructing a partial convex hull representation for a given 0–1 mixed-integer programming problem by using the reformulation–linearization technique (RLT). We derive a separation problem that projects the extended space of the RLT formulation into the original space, in order to generate a cut that deletes a current fractional solution. Naturally, the success of such a partial convexification based cutting plane scheme depends on the process used to tradeoff the strength of the cut derived and the effort expended. Accordingly, we investigate several variable selection rules for performing this convexification, along with restricted versions of the accompanying separation problems, so as to be able to derive strong cuts within a reasonable effort. We also develop a strengthening procedure that enhances the generated cut by considering the binariness of the remaining unselected 0–1 variables. Finally, we present some promising computational results that provide insights into implementing the proposed cutting plane methodology.
41948538
Enhanced Model Representations for an Intra-Ring Synchronous Optical Network Design Problem Allowing Demand Splitting
In this paper, we consider a network design problem arising in the context of deploying synchronous optical networks (SONET) using a unidirectional path switched ring architecture, a standard of transmission using optical fiber technology. Given several rings of this type, the problem is to find an assignment of nodes to possibly multiple rings, and to determine what portion of demand traffic between node pairs spanned by each ring should be allocated to that ring. The constraints require that the demand traffic between each node pair should be satisfiable given the ring capacities, and that no more than a specified maximum number of nodes should be assigned to each ring. The objective function is to minimize the total number of node-to-ring assignments, and hence, the capital investment in add-drop multiplexer equipments. We formulate the problem as a mixed-integer programming model, and propose several alternative modeling techniques designed to improve the mathematical representation of this problem. We then develop various classes of valid inequalities for the problem along with suitable separation procedures for tightening the representation of the model, and accordingly, prescribe an algorithmic approach that coordinates tailored routines with a commercial solver (CPLEX). We also propose a heuristic procedure which enhances the solvability of the problem and provides bounds within 5--13% of the optimal solution. Promising computational results are presented that exhibit the viability of the overall approach and that lend insights into various modeling and algorithmic constructs.
12876856
Virtual cell in mobile computer communications
In this paper, we design and develop a virtual cell approach for the transmission of IP datagrams in mobile computer communications. A virtual cell consists of a group of physical cells whose base stations are implemented by remote bridges and interconnected via high-speed datagram packet-switched networks. Host mobility is supported at the data link layer by virtual cell protocol (VCP) using the distributed hierarchical location information of mobile hosts. As far as the IP layer is concerned, it appears within a virtual cell as if the communication between two mobile hosts in different physical cells were taking place directly as in the same physical cell. Between virtual cells, a one-hop forwarding pointer from a mobile host's native virtual cell to its current virtual cell is maintained at the VCP layer. This means that the combination of the existing routing protocols of the IP layer and the forwarding pointer maintained at the VCP layer between virtual cells gives the same effect of having a fully duplicated location information among virtual cells for the global mobile network. Thus, the virtual cell approach eliminates the necessity of IP-level mobile host protocols that may interfere with the conventional IP protocol in a practical sense. In addition, given mobility and communication patterns among physical cells, it achieves a logically flexible coverage area of a virtual cell so as to minimize the total communication cost for the global mobile network where inter-virtual cell communication is more expensive than intra-virtual cell communication (K. Lim and Y.-H. Lee, IEEE Personal, Indoor and Mobile Radio Communications PIMRC'94, pp. 1237-1241, Sep. 1994; K. Lim, Y.-H. Lim and Y.-H. Lee, IEEE ICC'95, pp. 1839-1843, June 1995). To demonstrate the correct operations of VCP and measure data which are used as parameters to a performance model for the virtual cell system, we implement VCP on a simulated environment. The performance analysis of the virtual cell system is out of scope in this paper and one is referred to K. Lim, Y.-H. Lim and Y.-H. Lee, Proc. 10th Int. Conf. Information Networking ICOIN-10, pp. 551-560, Jan. 1996.
9836575
Optimal production-distribution planning in supply chain management using a hybrid simulation-analytic approach
Production-distribution planning is the most important activity in supply chain management (SCM). To solve this planning problem, either analytic or simulation approaches have been used. However these two approaches have their own demerits in problem solving. We propose a hybrid approach which is a specific problem solving procedure combining analytic and simulation methods to solve production-distribution problems in supply chains. The machine capacity and distribution capacity constraints in the analytic model are considered as stochastic factors and are adjusted by the proposed specific process according to the results from an independently developed simulation model which includes general production-distribution characteristics.
9193373
Pfair scheduling of periodic tasks with allocation constraints on multiple processors
Summary form only given. Pfair scheduling for periodic tasks on multiple processors in a time slotted environment can not only guarantee task deadlines to be respected, but also make tasks execute at steady progressive rates. We consider pfair schedulability of periodic tasks with allocation constraints in the sense that some tasks can only be assigned to one or more specified processors. The contributions of the paper lie in the following four aspects. Firstly, we prove that there exists pfair schedule in the case that fixed tasks are assigned to disjoined processor subsets. Secondly, we give a sufficient and necessary condition of the existence of pfair schedule for periodic tasks with arbitrary allocation constraints. Thirdly, we show that pfair schedulability test of periodic tasks with arbitrary allocation constraints can be done in polynomial time. Finally, an online approximate pfair scheduling algorithm called HPA (hierarchical pfair algorithm) is proposed for scheduling fixed and migrating tasks. With HPA although idea a fixed task is not guaranteed to respect its deadline completely, the amount of time by which it misses its deadline is bounded.
749990
Optimal Checkpointing of Real-Time Tasks
Analytical models for the design and evaluation of checkpointing of real-time tasks are developed. First, the execution of a real-time task is modeled under a common assumption of perfect coverage of on-line detection mechanisms (which is termed a basic model). Then, the model is generalized (to an extended model) to include more realistic cases, i.e., imperfect coverages of on-line detection mechanisms and acceptance tests. Finally, we determine an optimal placement of checkpoints to minimize the mean task execution time while the probability of an unreliable result (or lack of confidence) is kept below a specified level. In the basic model, it is shown that equidistant intercheckpoint intervals are optimal, whereas this is not necessarily true in the extended model. An algorithm for calculating the optimal number of checkpoints and intercheckpoint intervals is presented with some numerical examples for the extended model.
10753893
Evaluation of Error Recovery Blocks Used for Cooperating Processes
Three alternatives for implementing recovery blocks (RB's) are conceivable for backward error recovery in concurrent processing. These are the asynchronous, synchronous, and the pseudorecovery point implementations. Asynchronous RB's are based on the concept of maximum autonomy in each of concurrent processes. Consequently, establishment of RB's in a process is made independently of others and unbounded rollback propagations become a serious problem. In order to completely avoid unbounded rollback propagations, it is necessary to synchronize the establishment of recovery blocks in all cooperating processes. Process autonomy is sacrificed and processes are forced to wait for commitments from others to establish a recovery line, leading to inefficiency in time utilization. As a compromise between asynchronous and synchronous RB's we propose to insert pseudorecovery points (PRP's) so that unbounded rollback propagations may be avoided while maintaining process autonomy. We developed probabilistic models for analyzing these three methods under standard assumptions in computer performance analysis, i.e., exponential distributions for related random variables. With these models we have estimated 1) the interval between two successive recovery lines for asynchronous RB's, 2) mean loss in computation power for the synchronized method, and 3) additional overhead and rollback distance in case PRP's are used.