Section: 5.42 Support of Non-seamless WLAN offload
Content: Non-seamless WLAN offload is an optional capability of a UE supporting WLAN radio access. The architecture to support authentication for Non-seamless WLAN offload in 5GS is defined in clause 4.2.15. A UE supporting Non-seamless WLAN offload may, while connected to WLAN access, route specific data flows via the WLAN access without traversing the 5GC. These UE data flows are identified using URSP configuration for Non-Seamless Offload, or UE Local Configurations as defined in TS 23.503[ Policy and charging control framework for the 5G System (5GS); Stage 2 ]  [45]. For these data flows, the UE uses the local IP address allocated by the WLAN access network and no IP address preservation is provided between WLAN and NG-RAN. For performing the Non-seamless WLAN offload, the UE needs to acquire a local IP address from the WLAN access network and it is not required to connect to an N3IWF, ePDG or TNGF. If the WLAN access network is configured to require the 5GS based access authentication of the UE for connecting to the WLAN, the UE performs the authentication procedure for Non-seamless WLAN offload in 5GS defined in clause 4.2.15 and in Annex S of TS 33.501[ Security architecture and procedures for 5G System ]  [29]. After successful authentication, the UE is not considered to be entered in 5GS Registered state. The UE can send and receive traffic not traversing the 5GC and which is not under the control of the 5GC. A non-3GPP access network may be connected via SWa' to multiple PLMNs for 5G NSWO. In a roaming scenario the HPLMN may be reached by the UE via a WLAN access connected to more than one VPLMN. Therefore, a UE when roaming shall be able to indicate a specific selected VPLMN (e.g. using decorated NAI for 5G NSWO) through which the NSWO request should be sent towards the HPLMN. A non-3GPP access network may be connected to multiple SNPNs different from the Credentials Holder for 5G NSWO. When using the credentials owned by CH, the UE shall be able to indicate a specific selected SNPN (e.g. using decorated NAI for 5G NSWO) through which the NSWO request should be sent towards the CH in the following scenarios: - The CH hosts AUSF/UDM and the CH is reached by the UE via a WLAN access connected to a SNPN different from the CH as defined in Figure 4.2.15-3a. - The CH hosts AAA server and the CH is reached by the UE via a WLAN access connected to the AAA proxy in specific SNPN as defined in Figure 4.2.15-3b. A UE connected to a WLAN access network using 5GS credentials (as shown in Figure 4.2.15-1), may also be connected to the 5GC, for example to establish a PDU session. For example, the UE may connect to the 5GC either via another access type (such as NG-RAN), or via the same WLAN access network by performing the 5GS registration via Untrusted non-3GPP access procedure (using N3IWF) or interworking between ePDG connected to EPC and 5GS (using ePDG) defined in TS 23.502[ Procedures for the 5G System (5GS) ]  [3]. When a UE is connected to a WLAN access network (e.g. using 5GS credentials) and using an Untrusted non-3GPP access, the UE can perform Non-Seamless Offload of some or all data traffic to this WLAN access network sending the traffic outside the IPSec tunnel encapsulation as defined in URSP rules with Non-Seamless Offload indication. A UE may use the Registration procedure for Trusted non-3GPP access defined in clause 4.12a.2.2 of TS 23.502[ Procedures for the 5G System (5GS) ]  [3] and then determine to send some traffic (to be subject to Non-seamless WLAN offload) outside of the IPSec tunnel established with the TNGF. NOTE: A UE cannot first connect to a WLAN access network using 5GS credentials and without performing 5GS registration, and then later, on this WLAN access network, perform 5GS registration using the Trusted non-3GPP access procedure without first having to release the WLAN and then to establish a new WLAN association per the Registration procedure for Trusted non-3GPP access as defined in clause 4.12a.2.2 of TS 23.502[ Procedures for the 5G System (5GS) ]  [3]. When the UE decides to use 5G NSWO to connect to the WLAN access network using its 5GS credentials but without registration to 5GS, the NAI format for 5G NSWO is used whose realm is different than the realm defined for usage of Trusted non-3GPP access to the 5GC (defined in clauses 28.7.6 and 28.7.7 of TS 23.003[ Numbering, addressing and identification ]  [19]). The NAI format for 5G NSWO is defined in TS 23.003[ Numbering, addressing and identification ]  [19].