This paper examines two different examples of how No. 4 ESS software has evolved through restructuring to meet the needs of the changing No. 4 ESS environment. The two software areas that under went varying degrees of incremental restructure are Call Processing and Fault Recovery. We characterize the pre-restructure architec tures, discuss the motivation and rationale which led to restructure, and present and evaluate the post-restructure architecture for each software system.