Section: 8.2.1 Control Plane Protocol Stacks between the 5G-AN and the 5G Core: N2 8.2.1.1 General
Content: NOTE 1: N2 maps to NG-C as defined in TS 38.413[ NG-RAN; NG Application Protocol (NGAP) ]  [34]. Following procedures are defined over N2: - Procedures related with N2 Interface Management and that are not related to an individual UE, such as for Configuration or Reset of the N2 interface. These procedures are intended to be applicable to any access but may correspond to messages that carry some information only on some access (such as information on the default Paging DRX used only for 3GPP access). - Procedures related with an individual UE: - Procedures related with NAS Transport. These procedures are intended to be applicable to any access but may correspond to messages that for UL NAS transport carry some access dependent information such as User Location Information (e.g. Cell-Id over 3GPP access or other kind of User Location Information for Non-3GPP access). - Procedures related with UE context management. These procedures are intended to be applicable to any access. The corresponding messages may carry: - some information only on some access (such as Mobility Restriction List used only for 3GPP access). - some information (related e.g. with N3 addressing and with QoS requirements) that is to be transparently forwarded by AMF between the 5G-AN and the SMF. - Procedures related with resources for PDU Sessions. These procedures are intended to be applicable to any access. They may correspond to messages that carry information (related e.g. with N3 addressing and with QoS requirements) that is to be transparently forwarded by AMF between the 5G-AN and the SMF. - Procedures related with Hand-Over management. These procedures are intended for 3GPP access only. The Control Plane interface between the 5G-AN and the 5G Core supports: - The connection of multiple different kinds of 5G-AN (e.g. 3GPP RAN, N3IWF for Un-trusted access to 5GC) to the 5GC via a unique Control Plane protocol: A single NGAP protocol is used for both the 3GPP access and non-3GPP access; - There is a unique N2 termination point in AMF per access for a given UE regardless of the number (possibly zero) of PDU Sessions of the UE; - The decoupling between AMF and other functions such as SMF that may need to control the services supported by 5G-AN(s) (e.g. control of the UP resources in the 5G-AN for a PDU Session). For this purpose, NGAP may support information that the AMF is just responsible to relay between the 5G-AN and the SMF. The information can be referred as N2 SM information in TS 23.502[ Procedures for the 5G System (5GS) ]  [3] and this specification. NOTE 2: The N2 SM information is exchanged between the SMF and the 5G-AN transparently to the AMF.