This part mainly examines the DU and CU from ue to gnb to the core network, from the user plane to the control plane, the interfaces of each part, and the protocol stack. First of all, remember the connotation of each protocol, where it is used, and then remember the protocol stack. When doing the question, the protocols corresponding to the same layer must be the same.
Learn from the following link
5G architecture and protocol stack
5G NR protocol stack
5G air interface protocol stack
If you just memorize the answer, the routines of these pictures are similar. In fact, you only need to memorize two groups of pictures. One group is 6/7 in the column of UE, the second group is 6 in AMF, and then It is F1-AP for ue-amf and c ue-ngnb, GTP-U for ue-upf and u ue-ngnb,
UE-AMF
AMF-UE is exactly the same as UE-AMF
UE-UPF
Compared with UE-AMF, from ue to du, the third-layer RRC+NAS is replaced by SDAP, and the
SCTP+F1-AP between DU and CU is replaced by UDP+GTP-U
SCTP+NG- between CU and UPF The AP is replaced by UDP+GTP-U (maybe the user plane uses these two protocols)
C UE—NgNB protocol
It is similar to ue-AMF, but there is no NAS layer, and NG-AP is replaced by Xn-AP, and other places are exactly the same.
U UE—NgNB protocol
Exactly the same as UE-UPF, exactly the same.