2020). NR; Physical layer procedures for control. 3GPP. Available at: www.3gpp.org (accessed May 22, 2020). 3GPP Technical Specification (TS) 38.214 (2020). NR; Physical layer procedures for data. 3GPP. Available at: www.3gpp.org (accessed May 22, 2020). 3GPP Technical Specification (TS) 38.215 (2020). NR; Physical layer measurements. 3GPP. Available at: www.3gpp.org (accessed May 22, 2020). NG-RAN Architecture Colby Harper1 and Sasha Sirotkin 1 Pivotal Commware Inc., USA 2Intel Corporation, Israel Introduction With a high-level understanding of the whole 5G System (described in the previous chapter), we now dive into the details of the NG-RAN architectures. We use the plural term intentionally - not SO much because there are multiple NG-RAN architecture options that vendors and operators need to choose from (which is indeed the case), but because these options are defined in different standards development organizations and industry fora (not just 3GPP), for different use cases and development scenarios and even sometimes with different business objectives in mind. In this chapter we focus on standards-based NG-RAN architectures (even though some proprietary options are also covered), but one must understand that unlike, for example, the standards-based NR Uu (air) interface (described in Chapter 3), NG-RAN network standards are not as rigorous. In practice, while most implementations do try to follow them, the result is not always multi-vendor interoperable. When equipment from different vendors is used in the same network, it usually requires a fair amount of integration and interoperability testing - in particular, because there are no standards-based con- formance testing and certification programs for network architectures and interfaces (unlike the air interface). Oftentimes operators working with multiple RAN vendors chose to deploy equipment from only one vendor in a given geographical area in order to reduce the integration effort and potential interoperability issues. Therefore, NG-RAN architectures de