oduction and Background Central unit (upper layers of gNB protocols) RAN-CN RAN-CN RAN-CN interface interface interface (e)LTE (lower (lower (lower layers of layers of layers of Inter-BS interface protocols) protocols) protocols) Noncentralized architecture Centralized architecture Figure 7 Illustration of the non-centralized and centralized deployment scenarios [16,17]. The new 5G RAN architecture, as shown in Fig. 7, supports the following topologies in order to enable diverse use cases and deployment scenarios [16]: Non-centralized RAN architecture: In this scenario, full user-plane and control-plane radio protocol stacks are implemented at the gNB, for example, in a macrocell deploy- ment or an indoor (public or enterprise) hotspot environment. The gNBs can be con- nected to each other using any transport mechanism (e.g., Ethernet, optical fiber). However, it is assumed that the gNB is able to connect to other gNBs or eLTE eNBs3 through standard interfaces defined by 3GPP. Centralized RAN architecture: In this scenario, the upper layers of the radio protocol stack (PDCP and RRC layers) are implemented in the CU which is typically located in the edge cloud. Different functional splits between the CU and the DU(s) are also possi- ble, depending on the transport layer configuration. High-performance transport mechanisms, for example, optical transport networks (OTN), between the CU and the lower layers of the stack located at the DUs would enable advanced coordinated multi- point (CoMP) transmission/reception schemes and inter-cell scheduling optimization, which could be useful in high-capacity scenarios, or scenarios where inter-cell The eLTE eNB is the evolution of LTE (i.e., LTE Rel-15 and later) eNB that supports connectivity to EPC and 5GC. OTN is a set of optical network elements connected via optical fiber links that are able to provide transport, multiplexing, switching, and management functions as well as supervision and survivability of optical chan- nels carrying users' signals. Introduction and Backg