What is the difference between N1 interface and N2 interface in 5G?

Question

In every 5G diagram, they have the N1 interface directly connected to the UE. Is it really a direct connection? or is it still going through the radio? If so what is the difference from N2?

Answer 1

RAN uses N2 (control plane) and N3 (user plane) to interface to the core and transparent N1 interface to the user devices. N1 is a transparent interface from 5G-UE to AMF of core(via NG-RAN).

N1 interface is used by UE for transmitting non radio signalling between UE and AMF (something like NAS) which includes information related to connection, mobility and session related messages to the AMF which handles cases related to connection, mobility messages, but forwards session management info to SMF.

N2 interface supports control plane signalling between RAN and 5G core covering scenarios related to UE context management, PDU session/resource management procedures. N2 uses SCTP (NGAP) between 5GCN and access network.