The utmost priorities of SK Telecom's infrastructure outlined in this chapter are “Scalable, Cognitive, Automated, Lean and End-to-End”. The virtualization of Telco infrastructure has been expanded beyond the traditional data center to encompass even the areas of core and access network. This chapter presents the evolution direction of network infrastructure architecture that a Telco needs to achieve in the future based on the SK Telecom's enriched experiences in technology developments and commercialization and key considerations. It also proposes the ATSCALE architecture that SK Telecom aims to accomplish. The chapter presents architectural details with regard to the domains of the ATSCALE, namely, Software-defined RAN (SDRAN), Virtualized Core (vCore), Unified and Converged Transport Network (uCTN), Unified Orchestration (Unified-O), and Next-Generation OSS (NG-OSS) and describes each one of them in detail from the viewpoint of implementation technology.