My 3GPP 24.501 notes
4.1 Overview
The non-access stratum (NAS) described in 24.501 forms the highest stratum of the control plane between UE and AMF (reference point "N1" see 3GPP TS 23.501) for both 3GPP and non-3GPP access.
Main functions of the protocols that are part of the NAS are:
- support of mobility of the user equipment (UE) including also common procedures such as authentication, identification, generic UE configuration update and security mode control procedures;
- support of session management procedures to establish and maintain data connectivity between the UE and the data network; and
- NAS transport procedure to provide a transport of SMS, LPP, LCS, UE policy container, SOR transparent container and UE parameters update information payload.
Principles for the handing of 5GS security contexts and for the activation of ciphering and integrity protection, when a NAS signalling connection is established, are provided in subclause 4.4.
For the support of the above functions, the following procedures are supplied within this specification:
- elementary procedures for 5GS mobility management in clause 5; and
- elementary procedures for 5GS session management in clause 6.
Signalling procedures for the control of NAS security are described as part of the 5GMM common procedures in subclause 5.4.
Complete NAS transactions consist of specific sequences of elementary procedures. Examples of such specific sequences can be found in 3GPP TS 23.502.
The NAS for 5GS follows the protocol architecture model for layer 3 as described in 3GPP TS 24.007.