Retractable Contract Network for Distributed Scheduling

This paper is about distributed scheduling where individual agents have potentially conflicting interests. It is motivated by BT’s workforce scheduling problem, where multiple service providers have to serve multiple service buyers. The service providers and buyers all attempt to maximize their own utility. The overall problem is a multi-objective optimization problem; for example, one has to maximize completion rates and service quality and minimize travelling distances. In this paper, BT’s problem is modelled as an open constraint optimization system. Standard contract net is a practical strategy in distributed scheduling where agents may have conflicting objectives. In this paper, we have introduced a retractable contract net protocol, which we call RECONNET, that supports hill-climbing in the space of solutions. It is built upon a job-release and compensation mechanism. RECONNET is a general protocol, which could be used to implement complex meta-heuristic algorithms such as Tabu Search and Guided Local Search. A system based on RECONNET has been implemented for BT’s workforce scheduling problem. The software, which we call ASMCR, allows the management to have full control over the company’s multiobjectives. The manager generates a Pareto set of solution by defining, for each buyer and seller, the weights given to each objective. ASMCR gives service buyers and sellers ownership of their problem and freedom to maximize their performance under the criteria defined by the management. ASMCR took 5 to 15 minutes to complete when tested on real-sized problems. It has potential to be developed into practical solutions to BT’s workforce scheduling problem.