5G RAN ARCHITECTURE

Standalone option 5

• NGC (Next Generation Core Network): Consists of AMF, SMF and UPF. It is also called as 5GC(5G Core Network)
• AMF (Access and Mobility Management Function): Responsible for Registration, Connection, Reachability and Mobility Management, access authentication and authorization, and location services.
• SMF (Session Management Function): Responsible for PDU Session Management, IP Address Allocation. GTP-U Tunnel Management and Downlink Notification Management.
• UPF (User Plane Function): Forwards traffic between RAN and the Internet, packet forwarding, it is responsible for policy enforcement, lawful intercept, traffic usage reporting, and QoS policing.
• NG-RAN(Next Generation Radio Access Network): Consists of gNB/gNodeB(5G Base Station)
• gNB (gNodeB): A 5G Base Station is known as a gNodeB. It uses the New Radio (NR) air-interface and signalling protocols towards the end-user device. The gNB connects to an AMF for control plane signalling. The gNB connects to an UPF for the transfer of application data.
• ng-eNB (ng-eNodeB): Is connected to the 5G core network, i.e., an upgraded 4G Base Station. It connects to UE through LTE air interface and protocols. It is connected to 5G core network via NG-C and NG-U interface, i.e., the ng-eNodeB (ng-eNB) is capable of supporting 5G Core Network signalling procedure and is also capable of transferring application data to and from a UPF (User Place Functions).
• NG interface exists between 5GC and the base stations (i.e. gNB & ng-eNB).
• Xn interface exists between the base stations. Between gNB-gNB, between (gNB)-(ng-eNB) and between (ng-eNB)-(ng-eNB).

5G UPPER AND LOWER LAYER SPLIT ARCHITECTURE

• The Transport network which connects the Base Station to the Core Network is known as the Backhaul.
• The Connection between the Centralized Unit (CU) and the Distributed Unit (DU) is known as Mid haul.
• The Connection between the Radio Access Unit and the Radio Unit (RU) is known as Front haul.

5G CU/DU SPLIT BASE STATION ARCHITECTURE

• The 5G Core Network consists of many components like, AMF, SMF, UPF, AUSF, UDM, PCF, NSSF and AF. And it can connect/Manage multiple gNB(gNodeB).
• The gNB-CU is Centralized Unit(CU) and it can connect to multiple DU’s(Distributed Unit’s)
• The gNB-DU is Distributed Unit (DU) and it can manage multiple Radio Units (RU’s).

5G CONTROL PLANE – USER PLANE SEPARATION ARCHITECTURE

• The gNB-CU is further split into gNB-CU-CP and gNB-CU-UP. This separation allows independent scaling of the Base Station hardware. The CU-UP capability can be increased to support higher throughputs, without having to increase the capability and it minimize the latency towards DU (Distributed Unit).
• The CU-CP includes RRC and PDCP protocol stack layers and is responsible for RRC Signaling.
• The CU-UP includes SDAP and PDCP protocol stack layers and is responsible for handling application data.
• The DU includes RLC, MAC and L1 protocol stack layers and is responsible for scheduling the signaling data which comes from CU-CP and scheduling the application data which comes from CU-UP to the User Equipment (UE).

CU-UP SEPARATION ARCHITECTURE

• The CU-UP separation can include single CU-CP, Multiple CU-UP and Multiple DU.
• The connection of multiple CU-UP to a single DU means that each cell can have a choice of CU-UP.
• A first CU-UP could be used for eMBB application, the second can be used for URLLC application, The selection of appropriate CU-UP can form part of a Network Slicing implementation.
• The CU-CP and CU-UP are connected using E1 interface and it is used for only control plane signaling
• The CU-CP and the DU are connected using F1-C interface and it is used for only control plane signaling.
• The CU-UP and the DU are connected using F1-U interface and it is used only for transfer application data.
• The CU-UP is responsible for allocating GTP Tunnel Endpoint Identifiers(GTP TEID) for the uplink of the F1-U interface and it is also responsible for allocating GTP TEID for the downlink of the NG-U interface.

Interfaces

• NGAP interface exists between 5GC and the base stations (i.e. gNB & ng-eNB)
• NG-C: Control plane interface between NG-RAN and 5GC.
• NG-U: User plane interface between NG-RAN and 5GC.
• XnAP interface exists between the base stations. between gNB-gNB, between (gNB)-(ng-eNB) and between (ng-eNB)-(ng-eNB).
• Xn is the network interface between NG-RAN nodes.
• Xn-U stands for Xn User Plane interface and Xn-C stands for Xn Control Plane interface.
• E1AP interface is point-to-point interface between a gNB-CU-CP and a gNB-CU-UP
• E1 interface supports the exchange of signaling information between the gNB-CU-CP and gNB-CU-UP.
• F1-C: Control plane interface between CU-CP and DU
• F1-U: User plane interface between CU-UP and DU.
• X2AP interface exists Between en-gNB’s
• X2-C: Control plane interface between en-gNB’s.
• X2-U: User plane interface between en-gNB’s.