Non-access stratum (NAS) is a functional layer in the NR, LTE, UMTS and GSM wireless telecom protocol stacks between the core network and user equipment.
The NAS is defined in contrast to the Access Stratum which is responsible for carrying information over the wireless portion of the network.
A further description of NAS is that it is a protocol for messages passed between the User Equipment, also known as mobiles, and Core Nodes (e.g.
Once the User Equipment (UE) establishes a radio connection, the UE uses the radio connection to communicate with the core nodes to coordinate service.
The distinction is that the Access Stratum is for dialogue explicitly between the mobile equipment and the radio network and the NAS is for dialogue between the mobile equipment and core network nodes.