In addition to the 2G~5G mobile communication technologies defined by 3GPP, there are also wireless communication supported by non 3GPP such as Wi-Fi, Bluetooth and NTN (satellite communication) in the wireless communication system; 3GPP has introduced the support for non 3GPP in the 5G core network since Release17, which means that NTN and others can also access 5GC defined by 3GPP, and terminals can realize the mobility between 3GPP and non 3GPP; i. Interworking with non 3GPP This is to realize the interaction between the non-granted non 3GPP network and the 5G core network (5GC). The terminal can realize the movement between 3GPP and non 3GPP;
1、Interworking with non3GPP This is to realize the interworking between the non-granted non 3GPP network and the 5G core network (5GCN); during this period, the N3IWF will act as a gateway to the 5GCN and support the N2 and N3 interfaces to the 5GCN; the N3IWF will also provide a secure connection for the terminals (UEs) that are accessing the 5GCN through the non 3GPP network, and support IPsec between the UEs and the N3IWF. ii. IPsec between UE and N3IWF.
2、The interfaces, agreements and procedures, and QoS in the architecture for non-credit non 3GPP network interworking with the 5G core support control plane (CP) functionality, including registration and PDU session establishment, as well as user plane (UP) functionality, including non-credit non 3GPP access and QoS in N3IWF. Currently, the 3GPP specification only supports WLAN (Wireless Local Area Network (Wi-Fi) Access Network) as a non 3GPP access network;
3、Why do we need non 3GPP? Non-credit WLANs include public hotspots, home Wi-Fi, enterprise Wi-Fi, etc. that are not traditionally under the control of the mobile network operator By enabling convergence with individual 5GCNs that provide a variety of IP-based services, these non-credit non3GPP/WLANs can complement 3GPP radio access network coverage and address the following issues:
4、WLAN and 3GPP As shown in Figure (1) below untrusted WLAN and 3GPP mobile network can access 3GPP network before 4G/5G from untrusted WLAN through WAG (Wireless Access Gateway) and PDG (Packet Data Gateway). Wherein:The PDG comprises a subset of TTG (Tunnel Terminal Gateway) and GGSN functionality that works in concert with the TTG.The AAA server is used to authenticate the UE through the WAG using EAP-AKA/EAP-SIM authentication over the untrusted WLAN. CP (control) signaling between the TTG and the GGSN uses the GTPC agreement and establishes a PDP context for the user session. For each established UE session the IPsec tunnel terminates at the TTG and establishes the corresponding GTPU tunnel to the GGSN.
5、The 4G network can be accessed from untrusted WLANs through the ePDG (Evolved Packet Data Gateway) using EAP-AKA/EAP-AKA authentication and AAA server. the CP signaling between the ePDG and the PGW uses the GTPC/PMIP agreement and establishes the bearer for the user session. For each UE session established over the untrusted WLAN. the IPsec tunnel terminates at the ePDG and establishes the corresponding GTPU/GRE tunnel to the PGW. The dual-stack MIPv6 agreement can also be used to establish IPsec between the UE and the ePDG for CP signaling, and to establish a tunnel between the UE and the PGW for user-plane (UP) messaging.
