Content for  TS 23.402  Word version:  18.2.0

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8.2.3  3GPP Access to Untrusted Non-3GPP IP Access Handover with PMIPv6 on S2bp. 200

This clause shows a call flow for a handover when a UE moves from a 3GPP Access to an untrusted non-3GPP access network. PMIPv6/GTP is assumed to be used on the S5/S8 interface and PMIPv6 is used on the S2b interface.
Copy of original 3GPP image for 3GPP TS 23.402, Fig. 8.2.3-1: Handover from 3GPP Access to Untrusted Non-3GPP IP Access with PMIPv6 on S2b
Both the roaming (Figure 4.2.1-2) and non-roaming (Figure 4.2.1-1) scenarios are depicted in the Figure. In the roaming case, the vPCRF acts as an intermediary, sending the QoS Policy Rules Provision from the hPCRF in the HPLMN to the Serving-GW in the VPLMN. The vPCRF receives the Acknowledgment from the Serving-GW and forwards it to the hPCRF. In the non-roaming case, the vPCRF is not involved.
For connectivity to multiple PDNs the following applies:
  • If the UE is connected to both 3GPP access and non-3GPP access before the handover of PDN connections to untrusted non-3GPP access is triggered, steps 2 to 9 shall be skipped and the UE shall only perform step 10 for each PDN connection that is being transferred from 3GPP access.
  • If the UE is connected only to 3GPP access before the handover of PDN connections to untrusted non-3GPP access is triggered, steps 2 to 9 shall be performed. In step 3 the UE shall provide an APN corresponding to one of the PDN connections that are being transferred from 3GPP access. The UE shall then repeat step 10 for each of the remaining PDN connections that are being transferred from 3GPP access.
  • Step 11 shall be repeated for each PDN connection that is being transferred from 3GPP access.
Step 10 can occur in parallel for each PDN. Other impacts related to the handover for multiple PDNs are described in clause 8.1.
The optional interaction steps between the gateways and the PCRF in the procedures only occur if dynamic policy provisioning is deployed. Otherwise policy may be statically configured in the gateway.
Step 1.
The UE is initially attached to the 3GPP Access network.
Step 2.
The UE moves and attaches to an untrusted non-3GPP IP access network.
Step 3.
Access authentication procedure between UE and the 3GPP EPC may be performed as defined by TS 33.402.
Step 4.
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.
Step 5.
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.
Step 6A.
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.
Step 6B.
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.
Step 7.
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.
Step 8.
The ePDG and the UE continue the IKEv2 exchange and IP address configuration.
Step 9.
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.
Step 10.
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.
Step 11.
The PDN-GW shall initiate the PDN-GW Initiated PDN Disconnection procedure in 3GPP access as defined in clause or the PDN-GW Initiated Bearer Deactivation procedure as defined in clause of TS 23.401.



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