Re-engineering a signal control system

Abstract

Mass transit systems are making increased use of technology to bring more information to the desk of the operators. System performance is therefore directly impacted by the large amount of data being managed by the system, both coming to the operators from various sensors or subsystems, and command and control information going in the opposite direction. In order to achieve optimum performance, the system architecture must be adapted to accommodate this increased level of information and associated data traffic. The Jubilee Line Extension Mainline Control System in London, England, is a good representation of a railway control system that has to handle the increased information flow. This paper presents an overview of the architectural and design changes that were introduced in the Jubilee control system to handle the challenge of increased data. The goal of the system architecture changes was to improve the reliability, maintainability, recoverability, and performance characteristics of the overall signal control system. The major changes to the architecture included the introduction of IBM's System Network Architecture for use as the system's communications backbone and a distributed catalog mechanism to manage data distribution throughout the system. At the application level, a redesign of the alarm subsystem and access control subsystem were performed. The new design of the alarm subsystem resulted in the addition of a flow control mechanism as well as superior failure and recovery characteristics. The access control subsystem was changed to eliminate the need for a centralized server. For each change presented, an overview of the design prior to and after the change is given. The technical considerations are discussed from both a system and operational perspective.