A case study: Airlines reservations systems

The historical development of airlines reservations systems is traced. Characteristics are defined which are those of any real-time, conversational, highly interactive system. The structure of the system is described--agent terminal area, communications facilities, and central site. Lessons learned in the design, development, testing, implementation, and tuning of two generations of systems are discussed. These discussions include initial system design, simulations and systems measurement tools, systems stability and reliability, serial processing, parallel- or multiprocessors, split front-end back-end processing, storage hierarchy, standard and special communications disciplines, and flexibility versus performance. Unlike batch processing the real-time system cannot simply take more run time for a job that has been underestimated. It may well not be able to perform the job at all. Design of these systems is as much an art based on experience as a science and is an iterative process. Systems now being installed have capacities of 180 messages/s, accommodate 10 000 terminals which have access to a 10 billion-byte data base, and provide response times of less than 3 s.