Content for  TS 23.402  Word version:  18.3.0

The UE is initially attached to the 3GPP Access network.

The UE moves and attaches to an untrusted non-3GPP IP access network.

Access authentication procedure between UE and the 3GPP EPC may be performed as defined by TS 33.402.

The IKEv2 tunnel establishment procedure is started by the UE. The ePDG IP address to which the UE needs to form IPsec tunnel with is discovered as specified in clause 4.5.4. After the UE is authenticated, UE is also authorized for access to the APN. The procedure is as described in TS 33.402. As part of access authentication the PDN-GW identity is sent to the ePDG by the 3GPP AAA server. If the UE supports IP address preservation during handover from 3GPP Access to the untrusted non-3GPP IP access, the UE shall include its address (IPv4 address or IPv6 prefix /address or both) allocated when it's attached to 3GPP Access into the CFG_Request sent to the ePDG during IKEv2 message exchange. When the 3GPP AAA server has WLAN Location Information about the UE, it provides it over SWm to the ePDG together with the Age of this information. The WLAN Location information is provided to the ePDG when the 3GPP AAA server considers that location information coming from the WLAN AN used by the UE is trustable.

The ePDG sends the Proxy Binding Update (MN-NAI, Lifetime, Access Technology Type, Handover Indicator, GRE key for downlink traffic, UE Address Info, Additional Parameter) message to the PDN-GW. Access Technology Type is set to a value matching the characteristics of the non-3GPP access. The UE Address Info shall be set according to the CFG_Request in step 3. The ePDG shall not change the requested address(es) in the CFG_Request sent by the UE, and encode such address(es) in PBU and send to the PDN-GW. If the UE included the address in step 3, the ePDG sets the handover indicator to indicate Handoff between two different interfaces of the UE. The APN is used by the PDN-GW to determine which PDN to establish connectivity for, in the case that the PDN-GW supports multiple PDN connectivity. The ePDG creates and includes a PDN connection identity if the ePDG supports multiple PDN connections to a single APN.

If PCC is supported, the PDN-GW requires configuration for enforcing policy, the PDN-GW executes a PCEF-Initiated IP-CAN Session Modification Procedure with the PCRF as specified in TS 23.203.

The PDN-GW informs the 3GPP AAA Server of its PDN-GW identity and the APN corresponding to the UE's PDN Connection and obtains authorization information from the 3GPP AAA Server. The message includes information that identifies the PLMN in which the PDN-GW is located. The 3GPP AAA Server may update the information registered in the HSS as described in clause 12.

The PDN-GW processes the Proxy Binding Update message from the ePDG, updates the binding cache entry for the UE and responds with a Proxy Binding Acknowledgement (MN_NAI, Lifetime, GRE key for uplink traffic, UE Address Info, Charging ID, Additional Parameters) message. In the Proxy Binding Ack, the PDN-GW replies with the same IP address and/or prefix that was assigned to the UE earlier. If the corresponding Proxy Binding Update contains a PDN connection identity, the PDN-GW shall acknowledge if the PDN-GW supports multiple PDN connections to a single APN. At this point a PMIPv6 tunnel exists between PDN-GW and ePDG. Since this step is triggered by the Proxy Binding Update message from the ePDG in step 4, it can occur after step 4 and does not need to wait for step 5. The Charging Id provided is the Charging Id previously assigned to the PDN connection if the source access is a PMIP-based access or to the Default Bearer if the source access is GTP-based.

The ePDG and the UE continue the IKEv2 exchange and IP address configuration.

At the end of the handover procedure there is a default bearer for the UE that consists of an IPsec tunnel between the UE and the ePDG and a PMIPv6 tunnel between the ePDG and the PDN-GW.

For connectivity to multiple PDNs, the UE establishes connectivity to each PDN that is being transferred from 3GPP access, besides the PDN connection that was established in the steps 3-8, by executing the UE-initiated Connectivity to Additional PDN procedure specified in clause 7.6.1.

The PDN-GW shall initiate the PDN-GW Initiated PDN Disconnection procedure in 3GPP access as defined in clause 5.6.2.2 or the PDN-GW Initiated Bearer Deactivation procedure as defined in clause 5.4.4.1 of TS 23.401.