Non-3GPP Untrusted Wi-Fi to EPC Handover Call Flow

This section describes the non-3GPP untrusted Wi-Fi to EPC handover call flow.

Non-3GPP Untrusted Wi-Fi to EPC Handover Call Flow
Non-3GPP Untrusted Wi-Fi to EPC Handover Call Flow Description
StepDescription
1One or more PDU sessions are established between UE and ePDG through untrusted non-3GPP access. With the 5G NAS capability of UE, ePDG selects a combined PGW+SMF. UE sends the PDU session ID to the PGW+SMF.
2

UE discovers the E-UTRAN access and hands over the sessions from the currently used non-3GPP access system to E-UTRAN. For details on UE discovery of the 3GPP access system, see 3GPP TS 23.401, section 4.8.

UE sends an Attach request to MME for the Handover Attach request type. E-UTRAN routes the messages received from UE to MME as defined in 3GPP TS 23.401. UE includes the one of the APNs which are corresponding to the PDN connections in the source non-3GPP access. The APN is provided as defined in 3GPP TS 23.401.

3

MME and HSS perform authentication, which is followed by location update procedure and subscriber data retrieval to receive the APN information.

The MME selects an APN, an SGW and PDN gateway as defined in 3GPP TS 23.401. MME sends a Create Session Request message to SGW. This request includes information on IMSI, MME context ID, PDN-GW address, handover indication for the “handover” request type, and APN.

4

SGW sends a Create Session Request, which is handover indication, message to PDN-GW in the HPLMN as described in 3GPP TS 23.401. As the MME includes the handover indication information in the Create Session Request message, the SGW sends the GTPv2 Create Session Request message to PDN GW. This message includes details on IMSI, APN, handover indication, RAT type, S5-C TEID, S5-U TEID of the user plane, EBI, and user location information. The RAT type indicates the 3GPP IP access E-UTRAN technology type. If the UE supports IP address preservation and is included in PAA, the SGW configures the handover indication in the Creation Session Request. With this configuration, the PDN GW re-allocates the same IP address or prefix that was assigned to the UE while it was connected to the 3GPP IP access. With this configuration, SGW initiates the Policy Modification Procedure to the PCF.

As the handover indication is includes, the PDN GW does not switch the tunnel from non-3GPP IP access to 3GPP access system at this point.

SMF does not perform the UDM Registration as the registration happens during the Wi-Fi session establishment.

4aSMF detects the charging triggers with the information available in Step 3 against the charging triggers that are received during EPC session establishment.
4bSMF detects the PCF triggers with the information available in Step 3 against the Request Policy Control triggers that are received in the communication with PCF during EPC session establishment.
5Based on the detected armed Policy Control Triggers that are received in Step 4b, SMF sends the SM Policy Control Update request with the detected access parameters in Step 3 to PCF.
6PCF sends the SM Policy Control Update response, which is the SM policy decision, by including new or updated PCC rules.
7Based on the information received in Step 6 and existing policy data of EPC session, SMF prepares the information for the new or updated PCC rules.
8If SMF receives new PCC rules in Step 6, the SMF sends the Charging Update request, with the new rating-group having quota information, to CHF. This request includes the PDU session information with the new access params.
9CHF sends the multi-unit information as Charging Update response to SMF. The multi-unit information includes new quota information for the rating-group and the existing rating-group of EPC session, if any.
10SMF prepares the charging data of the received Charging Update Response that CHF sent.
11SMF sends the N4 Session Modification Request to UPF. This request includes the details on creation of UL and DL PDR, creation of QER, creation of URR for received new rating-group quota information, updated URR for modified quota information, and creation of FAR.
12UPF sends the UL tunnel information in the created PDR as N4 Session Modification response to SMF.
13SMF sends the GTPv2 Create Session response to S-GW. This response details on request accepted or request accepted partially, P-GW S2b F-TEID, PAA, APN-AMBR, bearer context creation, charging gateway address, and APCO.
14SGW sends the Modification Bearer request with handover indication to PGW for data path switching from Wi-Fi tunnel to 4G tunnel.
15PGW sends the N4 Session Modification request to delete the Wi-Fi tunnel and to configure DL tunnel information that is received in GTPv2 Create Session request for 4G tunnel in Step 4.
16UPF sends the N4 Session Modification response to SMF.
17SMF sends the GTPv2 Create Session request, which includes the bearer context list, to SGW. This list includes the DL Tunnel information for the end-user.
18SGW sends the GTPv2 Create Session response to SMF. This response includes details on request accepted or request accepted partially and bearer contexts.
19ePDG sends the GTPv2 Create Bearer resp (accepted EBIs with DL tunnel info to SMF
20SMF processes the Create Bearer response and derives the DL tunnel Information for the established bearer and the failed EBI list, if any. SMF sends the N4 session modification request to UPF for Wi-Fi tunnel. This request is to update the DL FAR with the DL tunnel information, RAT modification information, and to delete resources for the 4G tunnel. SMF also deletes the N4 resources of Wi-Fi tunnel for the received failed EBI list or the failed QFI list.
21UPF sends the N4 Session Modification Response with usage report to SMF.
22SMF sends the Charging Update request to CHF. This request includes the PDU session information with new access params and multi-usage report consisting of access-params and usage report that is received in Step 8.
23CHF sends the Charging Update Response with multi-unit information that contains quota information for the existing rating-groups to SMF.
24SMF+PGW-C initiates the GTPv2 DB Request toward SGW by including EBI or EBI list.
25SGW sends the GTPv2 DB Response toward SMF+PGW-C.
26

SMF sends the SM Policy Control Update request to UPF. This request includes the new access params and rule report for failed QFI list that is received from AMF as part of Create Bearer response.

PCF sends the SM policy decision as SM Policy Control Update response.

SMF processes the SM policy decision and handles it as PCF Initiation Modify procedure as defined in 3GPP 23.502 section 4.3.3.2.