Above image shows overall architecture from 3GPP TS 38.300 specification.
Xn interface exists between 2 base stations.
Xn-U stands for Xn User Plane
Xn-C stands for Xn Control Plane
NG interface is between 5GC and base station.
5G NR Xn Interface
Xn interface is between 2 or more NG-RAN
Functions of Xn-C
Xn Setup function
Error Indication function
Xn reset function
Xn configuration data update function
UE mobility management functions
Handover preparation function
Handover cancellation function
Retrieve UE Context function
RAN Paging function
Data Forwarding control function
Functions of Xn-U
Data transfer function
Flow control function
Assistance information function
Fast retransmission function
5G NR NG Interface
5G NR NG interface is between 5G RAN and 5G Core Network.
There are 2 interfaces in NG i.e NG-C, NG-U.
Functions of the NG interface
> Paging function
> UE Context Management function
> Mobility Management function
> PDU Session Management function
> Trace function
NG interface capabilities
> procedures to establish, maintain and release NG-RAN part of PDU sessions;
>procedures to perform intra-RA T handover and inter-RA T handover;
> the transfer of NAS signalling messages between UE and AMF;
> mechanisms for resource reservation for packet data streams.
5G NR E1 Interface
E1 interface is between gNB-CU-CP and gNB-CU-UP.
Functions of the E1 interface
> E1 interface management function
> E1 bearer context management function
> Trace function
5G NR F1 Interface
F1 interface is between gNB-CU and gNB-DU.
5G NR F2 Interface
F2 interface is between upper and lower part of PHY layer.
CPRI: Common Public Radio Interface.
CPRI is between the Radio Equipment Controllers and Radio Equipment.