The Cost Effectiveness of Telecommunication Service Dependability

In switching software applications, service quality has traditionally been achieved by the combination of two strategies: high reliance on defect elimination and fault recovery/tolerance. In turn, defect elimination has proven to be costly in staffing, and the implementation of fault tolerance has resulted in high hardware costs, by exclusively relying on proprietary hardware and by using monolithic recovery techniques external to the applications to achieve high quality service. The driving force for this strategy were: no unscheduled downtime, deferred maintenance, easy restart when needed, and easy growth and de-growth. While these objectives are still attractive, they can today be achieved in a more cost-effective way by increased reliance on standard software fault recovery components distributed closer to and inside the applications, and by using hardware sparing recovery at the system level. A recent trend toward rapid software customization will limit traditional software recovery techniques where absolutely necessary to satisfy performance requirements.