ROUTING IN A NETWORK WITH UNRELIABLE COMPONENTS

A new approach to the joint selection of primary and secondary routes in a network with unreliable components is presented. The mathematical model captures the changes in the operational characteristics of the network when it adapts to failures. Lagrangean relaxation and subgradient optimization techniques are used to obtain good heuristic solutions to the problem, as well as lower bounds to be used as benchmarks against which the quality of the solution is assessed. Results of numerical experiments are reported, and directions for further enhancements of the model are discussed.Information Systems Working Papers Serie

CAPACITY AND FLOW ASSIGNMENTS IN LARGE COMPUTER NETWORKS

This paper presents a model and the corresponding solution method for the problem of jointly selecting a set of primary routes and assigning capacities to the links in a computer communication network. The network topology and the traffic characteristics are known; a set of candidate routes for each communicating pair of nodes, and a set of candidate capacities for each link are also given. The goal is to obtain the least costly feasible design, where the costs include both capacity and queuing components. The resulting combinatorial optimization problem is solved using Lagrangean relaxation and subgradient optimization techniques. The method was tested on several topologies, and in all cases good feasible solutions, as well as tight lower bounds were obtained.Information Systems Working Papers Serie

The Travelling Salesman Problem and Related Problems

New formulations are presented for the Travelling Salesman problem, and their relationship to previous formulations is investigated. The new formulations are extended to include a variety of transportation scheduling problems, such as the Multi-Travelling Salesman problem, the Delivery problem, the School Bus problem and the Dial-a-Bus problem. A Benders decomposition procedure is applied on the new formulations and the resulting computational rocedure is seen to be identical to previous methods for solving the Travelling Salesman problem. Based on the Lagrangean Relaxation method, a new procedure is suggested for generating lagrange multipliers for a subgradient optimization procedure. The effectiveness of the bounds obtained is demonstrated by computational test results.Research supported, in part, by the Office of Naval Research under Contract N00014-75-C-0556

DISTRIBUTED COMPUTER SYSTEM DESIGN FOR LARGE DECENTRALIZED ORGANIZATIONS

This paper deals with the issue of designing distributed computer systems for large decentralized organizations. Specific problems addressed within this context include: determining the number of computer installations, choosing the sites that will receive these installations, deciding on the sizes of computers at different sites, configuring databases, allocating databases to computer installations and assigning users to computer installations. A class of decentralized organizations is identified for which decisions regarding the database configuration and the allocation of databases among processors can be effectively merged with decisions regarding the assignment of user nodes to processors. For these organizations, the design problem is formulated as an integer programming model. A brief outline of an effective solution procedure is provided and potential uses of the model as a design tool is demonstrated through a number of experiments

CAPACITY AND FLOW ASSIGNMENTS IN LARGE COMPUTER NETWORKS

This paper presents a model and the corresponding solution method for the problem of jointly selecting a set of primary routes and assigning capacities to the links in a computer communication network. The network topology and the traffic characteristics are known; a set of candidate routes for each communicating pair of nodes, and a set of candidate capacities for each link are also given. The goal is to obtain the least costly feasible design, where the costs include both capacity and queuing components. The resulting combinatorial optimization problem is solved using Lagrangean relaxation and subgradient optimization techniques. The method was tested on several topologies, and in all cases good feasible solutions, as well as tight lower bounds were obtained.Information Systems Working Papers Serie

Reducing Internet Auction Fraud

When it comes to online auctions, “caveat emptor” is an understatement

A system for routing and capacity assignment in computer communication networks

The joint problem of selecting a primary route for each communicating pair and a capacity value for each link in computer communication networks is considered. The network topology and traffic characteristics are given; a set of candidate routes and of candidate capacities for each link are also available. The goal is to obtain the least costly feasible design where the costs include both capacity and queuing components. Lagrangean relaxation and subgradient optimization techniques were used in order to obtain verifiable good solutions to the problem. The method was tested on several topologies, and in all cases good feasible solutions, as well as tight lower bounds were obtained

Batch Sizing and Scheduling in Serial Multistage Production Systems

The authors propose a procedure to model and determine the optimal batch sizes and their schedule in a serial multistage production process with constant demand rate for the final product. The model takes into consideration the batch setup time in each stage, the processing times of a batch as a function of batch size and production stage. It considers the holding and shortage costs of the final product, and the setup and processing costs at each stage of the production process. The objective is to maximize the net profit per unit of time derived from selling the final products. We report on extensive computational experiments that tested the impact of different factors on the objective function and the optimal batch size. A feature unique to this paper is the concentration on multistage serial systems consisting of hundreds of stages in the production process, in such systems a batch can spend from one to eight months in the production process. Batch sizing and scheduling has a great impact on the net revenues derived from the production facility. Due to the tight tolerances of the production process which are computer controlled, setup and processing times are deterministic

Warranty Policy Impact on Net Revenues as a Function of Part Replacements and Optional Purchases

Warranty rebate policies which require that the customer return to the retailer for replacements may provide both costs and benefits to the retailer. These benefits could include purchase of upgrades, additional related products, snacks and merchandise from different parts of the store, which will be made while the customer is waiting for the replacement. These benefits have not been studied in depth as most articles on warranties have focused on minimizing replacement costs. Moreover, there are two types of replacement patterns which have not been compared in conjunction with costs of replacement and returns from additional sales generated by return to the store to utilize the warranty. These are the case of the product that gradually wears out (i.e. tires and batteries) versus the product has a high failure rate in the initial period and then after adjustments are made the subsequent periods show lower rates of deterioration. An example of this type of product may be TV sets, complex electronic components and cellular phones. Using simulations which include marginal revenues from original sales and warranty utilization as more visits are made to replace parts and revenue is gained from additional sales, marginal revenue from added sales increase in positive linear fashion. As the reimbursement rate increases mean net revenues per period decrease but by less than the reimbursement amount. Cut-off points can be set for expected mean net revenues using reimbursement decline rates and varying amounts of marginal revenue. Two different types of failure rates are compared, initially high failure as in electronic devices versus gradually increasing failure rates as a function of age. Initially high rates of failure in conjunction with marginal revenues from additional purchase that are greater than zero and initial losses that are low may be more lucrative than average revenues from gradually increasing wear out replacements. Moreover, minimal levels of additional purchases, initial loss in value and rate reduction per number of periods can be established based on realistic simulation data in order to indicate how profits can be maximized