5G Node Funtional Split - gNB , AMF, SMF, UPF

 Keeping it simple for clarity of understanding.
Let's consider as two part :

Part 1: NG-RAN  -->  gNB/ng-eNB
Part2 : 5GC          --> AMF, SMF, UPF

gNB/ng-eNB Functionality:

1. RRM - Radio Resource Magament 
2. Radio Bearer Control
3. Radio Admission Control 
4. Connetion Mobility Control
5. Dynamic Resource Allocation (Sceduling on UL and DL)
6. IP Header Compression , Encryption and Integrity Protection of Data
7. AMF Selection during Registration when no routing to AMF can be dterimied from the onformation provided by UE.
8. Rounting of user plane data towards UPF
9. Routing of Control plane Information towards AMF

AMF Functionalty:

1. Mobility Management 
2. Support Intra and Inter System Mobility
3. Registraion Area Managament 
4. Idle Mode UE Reachability
5. SMF Selection
6. NAS Signalling 
7. NAS and AS Security

SMF Functionality:

1. Session Mangement 
2. UE IP addrress allocation and management 
3. Downlink Data Notification
4. Selection and Control of User Plane Function 

UPF Funtionality:

1. Anchonr Point for Intra/Inter-RAT Mobility 
2. SDF to QoS flow mapping
3. Packet Routing and Forwarding
4. Packet inspection and User plane part of policy rule enforcement
5. Downlink packet buffering and downlink data notification triggering