plications. The mid-haul transport network connects the CU to the DU. The DU comprises the Radio Link Control (RLC), Medium Access Control (MAC), and Physical (PHY) layers, along with the brain of the radio base station, the scheduler. The DU is a logical node hosting the RLC, MAC, and PHY layers of the gNB, and its operation is partly controlled by the CU. The components in the DU are responsible for rate adaptation, channel coding, modulation, and scheduling radio resources among the UEs in its coverage. One DU supports one or multiple cells. One cell is supported by one DU. The DU is connected to the CU by an F1 interface. This is highly time-sensitive and must operate within the guardrails of the latency requirements, which are in the order of milliseconds. The DU can be located in near- edge data centers or can be collocated with the Remote Units (RUs) for far-edge sites. End-to-End Architecture Components, Concepts, Security, and Transport The RU is the entity that is deployed at the cell sites, also known as Remote Radio Head (RRH). It connects to the DU through a CPRI or an eCPRI interface. To summarize, the access network comprises the entities that control over-the-air communication between the UE and the 5G network. We will get into the details of this communication in upcoming chapters. The packet core network The packet core network in 5G comprises multiple independent NFs that have different roles and responsibilities. They are built on cloud-native development principles and operate following a producer-consumer model. Each of these NFs provides a set of services to different NFs and similarly, they consume services from other NFs. Some of the most popular and essential NFs are the Access Management Function (AMF), Session Management Function (SMF), UPF, Charging Function (CHF), Unified Data Manager (UDM), Policy Control Function (PCF), and SO on. These NFs provide mobility management, session management and control, user plane and data processing, charging, subscription management, traffic policin