As mobile operators transition from 4G to 5G, one of the biggest parts of the mobile network experiencing transformation is the Radio Access Network (RAN). This transformation includes virtualization, disaggregation, open interface, intelligence, and cloudification, which are foundational components to an Open RAN architecture and complements the service-based architecture envisioned for 5G. Today, mobile networks typically consist of proprietary software integrated onto customized hardware designed by a single mobile network supplier. Network upgrades or fixes require systematic deployment and validation to each of the network subsystem functions and, in some cases, lead to an entire network overhaul. Mobile operators are locked into the development, release pace, and schedule of the network supplier, which can significantly impact network operation, offered services, and deployment plans. This industry dynamic increases costs, slows innovation, and reduces competition. The industry is attempting to change this single vendor paradigm (‘vendor lock’) by developing industry standards to disaggregate proprietary software from the hardware and open proprietary interfaces between network subsystems and functions to allow for network supplier interoperability. With a recent increase in mobile network operators (MNOs) trials, industry Plugfests, and standards development, the industry has quickened the pace towards achieving Open RAN, which has the vision of RAN components as a virtual software application capable of working on any bare metal hardware operated with orchestration and automation. The mobile industry is at a tipping point where non-traditional network suppliers are gaining momentum in developing Open RAN solutions that are maturing and becoming commercially viable, reliable, and scalable to the operator community. MNOs are assessing many factors and dependencies that are key to the transition of mobile networks to Open RAN, including the commercial and economic viability of Open RAN. As part of the considerations, MNOs must leverage current infrastructure investments to expand networks while developing a road map for future growth and purchase cycles. For several years, CableLabs evaluated the progress of Open RAN architecture and conducted several lab investigations in collaboration with Telecom Infra Project (TIP), O-RAN Alliance, and the National Telecommunications and Information Administration (NTIA). To assist in this assessment, CableLabs undertook an investigation of Open RAN transition approaches and key indicators for assessment with learnings from lab activities of industry generated and representative common operator deployment scenarios. As a result, this paper will address the following topics1: - Analyze the current state of the Open RAN ecosystem. - Discuss learnings of external and internal CableLabs Open RAN test activities. - Develop an Open RAN transition approach with assessment criteria.