 compatibility. For example, LTE was first introduced in Release 8, and it is still evolving today with Release 14 and Release 15. Meanwhile in parallel, 3GPP introduced the 5G new radio (NR) in Release 15. 3GPP started the study of 5G NR in September 2015 with the goal and vision to address IMT-2020 requirements. 3GPP technical report (TR) 38.913 describes scenarios, key performance require- ments, and requirements for architecture, migration, supplemental services, operations, and testing. This study completed in March 2017 with 3GPP TR 38.912 from Release 14 that captures a set of features and capabilities for the new radio access technology along with a study of their feasibility. 3GPP began to develop the 5G specification in two phases. Release 15 marks the first phase of 5G specifications, whereas Release 16 covers the second phase. Even work from Release 15 on NR ac- cess got split into three phases addressing different network operator demands. This is because some operators wanted to deploy 5G radio technology in combination with their existing LTE net- works-what became known as non-standalone (NSA) mode: Early Release 15 drop: Focused on the NSA NR architecture that allows operators to add an NR base station (called the gNB) to existing LTE base stations (eNB) in a system architecture still based on the 4G mobile core (known as the Evolved Packet Core [EPC]). Main Release 15 freeze: Focused on a standalone NR (SA NR) architecture in which NR gNBs connect to the 5G Core network (5GCN) without any LTE involvement. This would be more suitable to new network deployments that did not need to coexist with any existing LTE net- work infrastructure. Late Release 15 drop: Included support for an architecture where LTE base stations can be part of an SA NR network with two different deployment options: 1) control plane is assisted via the NR base station; 2) control plane is assisted via LTE base station. Please refer to 3GPP TR 38.801 (see the "References" section) if you are interested in the details of the ar