A mathematical model and scheduling heuristics for satisfying prioritized data requests in an oversubscribed communication network

Providing up-to-date input to users' applications is an important data mana gement problem for a distributed computing environment, where each data sto rage location and intermediate node may have specific data available, stora ge limitations, and communication links available. Sites in the network req uest data items and each request has an associated deadline and priority. I n a military situation, the data staging problem involves positioning data for facilitating a faster access time when it is needed by programs that wi ll aid in decision making. This work concentrates on solving a basic versio n of the data staging problem in which all parameter values for the communi cation system and the data request information represent the best known inf ormation collected so far and stay fixed throughout the scheduling process. The network is assumed to be oversubscribed and not all requests for data items can be satisfied. A mathematical model for the basic data staging pro blem is introduced. Then, three multiple-source shortest-path algorithm-bas ed heuristics for finding a near-optimal schedule of the communication step s for staging the data are presented. Each heuristic can be used with each of four cost criteria developed. Thus, 12 implementations are examined. In addition, two different weightings for the relative importance of different priority levels are considered. The performance of the proposed heuristics are evaluated and compared by simulations. The proposed heuristics are sho wn to perform well with respect to upper and lower bounds. Furthermore, the heuristics and a complex cost criterion allow more highest priority messag es to be received than a simple-cost-based heuristic that schedules all hig hest priority messages first.