16.11 Handover procedure from WLAN on S2a to 3GPP access

23.4023GPPArchitecture enhancements for non-3GPP accessesRelease 18TS

This procedure is as in clause 8.2.1.1 (GTP-based S5/S8 for E-UTRAN), clause 8.2.1.2 (PMIP-based S5/S8 for E‑UTRAN), clause 8.2.1.3 (GTP-based S5/S8 for UTRAN/GERAN) and clause 8.2.1.4 (PMIP-based S5/S8 for GERAN/UTRAN) with the following differences:

– Step 1. There is a GTP or PMIP tunnel between TWAN and PGW.

– Step 18 in 8.2.1.1, step 19 in clause 8.2.1.2 and step 17 in clause 8.2.1.3. The PDN GW shall initiate resource allocation deactivation procedure in the TWAN as defined in clause 16.4.

For handovers from GTP-based S2a to GTP-based S5/S8 the following additional changes apply:

For emergency sessions:

– On step 3, the UE sends an Attach Request to the MME with Request Type indicating "handover for emergency services". The message from the UE is routed by E-UTRAN to the MME as specified in TS 23.401 [4] (E-UTRAN). The UE shall not include any APN.

– On step 4, the MME shall contact the HSS and attempt to authenticate the UE as described in TS 23.401 [4].

– On step 5, if the UE has been successful authenticated, the MME may perform location update procedure and subscriber data retrieval from the HSS as specified in TS 23.401 [4] by which the "PDN GW currently in use for emergency services" is sent to the MME as part of the subscription information. Since the Request Type is "handover for emergency services", the "PDN GW currently in use for emergency services" conveyed from the HSS to the MME will be stored in PDN subscription context. The MME receives information on all the PDNs the UE is connected to over the non-3GPP access in the Subscriber Data obtained from the HSS. If the UE has been authorized but not authenticated, Step 5 is skipped.

– On step 6, the MME selects the emergency APN, and a serving GW as described in TS 23.401 [4]. If the UE has been successfully authenticated and is not roaming, and based on operator configuration, the MME uses the "PDN GW currently in use for emergency services" received from the HSS as anchor PDN GW. Otherwise, e.g. if the UE has not been successfully authenticated, or the UE is roaming, or based on operator configuration (e.g. the network supports handovers to/from HRPD), the MME shall use the PDN GW that is statically configured in the MME Emergency Configuration Data. The MME sends a Create Session Request (including IMSI, MME Context ID, PDN GW address, Handover Indication, emergency APN) message to the selected Serving GW. Since the Request Type is "handover for emergency services", a Handover Indication information is included.

For non-emergency and emergency sessions:

– On step 9 of clause 8.2.1.1 and step 11 of 8.2.1.3: the Charging Id provided by the PGW to the default and dedicated bearers in 3GPP access is the Charging Id previously assigned to the corresponding default and dedicated bearers (i.e. bearer with the same QCI and ARP) of the PDN connection in the non-3GPP access on the S2a interface, although the Charging Id still applies to the non-3GPP access.

NOTE 1: For UTRAN/GERAN access, the dedicated bearer establishment does not take place along with the default bearer establishment (i.e. sending of Create Session Response message). For E-UTRAN access, depending upon the support of the piggybacking feature in the network, the dedicated bearer can be created as part of default bearer establishment or immediately afterwards.

– On step 13 of clause 8.2.1.1 and step 14 of 8.2.1.3: the Charging Id previously in use for the default and dedicated bearers in the non-3GPP access on the S2a interface now applies to the corresponding default and dedicated bearers in 3GPP access (i.e. bearer with the same QCI and ARP as in non-3GPP access).