In recent years, building, maintaining, and evolving proprietary network systems for telecom-grade applications that are highly available and “always on” have become increasingly prohibitive from the perspective of cost, risk management, time to revenue, and so on. The custom-built approach becomes even less cost effective as Communications Service Providers (CSPs) move toward offering cloud-based services, where they have to compete with non-traditional providers that offer such services on networks built using Commercial Off-The-Shelf (COTS) building blocks.

A change in market dynamics is causing a fundamental paradigm shift in industry’s thinking: Instead of continuing to invest precious Research and Development (R&D) resources and dollars to build expensive, special-purpose proprietary systems with the hope that they will never fail, industry leaders are now assuming that there will be hardware and software failures and thus designing systems and applications that continue to provide end-user service in the presence of such failures. 

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refer to : http://xtca-systems.com/articles/engineered-cots-network-systems/