The following procedure is used to handover one or more PDN connections from 3GPP access to the Trusted WLAN.The steps involved in this procedure are depicted below for both the non-roaming and roaming cases. It is assumed that while the UE is served by the 3GPP access, PMIPv6 or GTP tunnel(s) are established between the Serving-GW and the PDN-GW in the EPC.
In the Local Breakout case, the 3GPP AAA Proxy forwads messages from the 3GPP AAA Server in the HPLMN to the PDN-GW in the VPLMN and vice versa. Messages between the PDN-GW in the VPLMN and the hPCRF in the HPLMN are forwarded by the vPCRF in the VPLMN. In the home routed roaming and non-roaming cases, the vPCRF and the 3GPP AAA Proxy are not involved, except for the authentication and authorization in step 2.
For connectivity to multiple PDNs the following applies:
If the UE is connected to both 3GPP access and TWAN before the handover of PDN connection(s) to Trusted WLAN is triggered, steps 1 to 4 shall be skipped and the UE shall only perform step 5 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 connection(s) to Trusted WLAN is triggered, steps 1 to 4 shall be performed. The UE shall then repeat step 5 for each of the PDN connections that is being transferred from 3GPP access.
Step 6 shall be repeated for each PDN connection that is being transferred from 3GPP access.
Step 5 can occur in parallel for each PDN connection. Other impacts related to the handover for multiple PDNs are described in clause 8.1
The UE is connected in the 3GPP access and has PMIPv6 or GTP tunnel(s) on the S5/S8 interface.
The UE discovers the trusted WLAN access and determines to transfer one or more of its active PDN connections from the currently used 3GPP access to the discovered trusted WLAN.
The UE performs access authentication and authorization in the trusted WLAN. This step is the same as step 2 of the initial attach procedure in clause 16.2.1
for non-emergency sessions and in clause 16.2.1a
for emergency sessions, where in this case Multi-Connection Mode is requested by the UE.
For emergency sessions, following modifications apply:
During authentication and authorization, the HSS shall provide the AAA server with the "PDN-GW currently in use for emergency services", if available, as part of the subscription information, relayed by the AAA server to the TWAN;
If the UE indicated an handover attach in step 2 is non-roaming and has been successfully authenticated, based on operator policy, the TWAN may select the "PDN-GW currently in use for emergency services" as anchor PDN-GW. Otherwise, e.g. if the UE indicated an handover attach in step 2 and has been authorized but not authenticated), or the UE is roaming, or based on operator configuration (e.g. the network supports handovers to/from HRPD), the TWAN shall select the PDN-GW that is statically configured in the TWAN Emergency Configuration Data.
TWAN sends EAP success to the UE and completing EAP authentication. This step is the same as step 8 of the initial attach procedure in clause 16.2.1
If NSWO is authorized for the UE in step 2, anytime after step 3 the UE may send a L3 attach request to the TWAN for NSWO and receive the address or prefix of the NSWO from TWAN.
The UE performs UE-initiated connectivity request procedure for Multi-Connection Mode according to clause 16.8.1
with the following exception:
The UE sends a PDN Connectivity Request message to the TWAN with Request Type indicating "Handover".
The UE indicates the APN corresponding to the PDN connection which is being handed over to TWAN in the PDN Connectivity Request message. If the APN is not provided, and the subscription context from HSS/AAA contains a PDN-GW identity and APN pair corresponding to the default APN, the TWAN uses the default APN for non-emergency sessions and the emergency APN for emergency sessions.
Upon receiving the PDN Connectivity Request message, the TWAN selects the PDN-GW as indicated in the subscription data received from the 3GPP AAA Server and sends Create Session Request to the selected PDN-GW. Since the Request Type is "Handover", a Handover Indication is included in the Create Session Request. In the case of emergency sessions when the UE has been authorized but not authenticated, the TWAN selects the PDN-GW that is statically configured in the TWAN Emergency Configuration Data.
Since it is a handover, the IP-CAN Session Establishment is not performed. The PDN-GW may execute a PCEF-Initiated IP CAN Session Modification Procedure with the PCRF as specified in TS 23.203 to report e.g. change in IP-CAN type.
The PDN-GW shall initiate the PDN-GW Initiated PDN Disconnection procedure in 3GPP access as defined in clause 188.8.131.52
or the PDN-GW Initiated Bearer Deactivation procedure as defined in TS 23.401, clause 184.108.40.206
Depending upon the active PCC rules, the PDN-GW may create dedicated bearers on S2a interface. And in that case, it applies the Charging ID previously in use for the corresponding dedicated bearer(s) while the UE was connected to the 3GPP IP access (i.e. bearer with the same QCI and ARP as in 3GPP access).
This procedure is as in clause 220.127.116.11
with the following differences:
Step 5 c.
Upon receiving the PDN Connection Request message, the TWAN selects the PDN-GW as indicated in the subscription data received from the 3GPP AAA Server and sends the Proxy Binding Update to the selected PDN-GW by setting the Handover Indicatior to indicate handoff between two different interfaces of the UE. The details of the messages and parameters to be used are described in Steps 6 and 8 in clause 8.2.2
. Additionally, the Proxy Binding Update includes the current TWAN Identifier as described in clause 16.1.7
and the UE Time Zone.