A.4 Call Flow for TSCM and EPC-routed access

29.2733GPP3GPP EPS AAA interfacesEvolved Packet System (EPS)Release 18TS

Figure Annex A.4-1 describes a successful call flow for TSCM for EPC-routed access, i.e with S2a connectivity being granted to the UE.

Figure Annex A.4-1: TWAN Authentication and Authorization Procedure for TSCM – successful case

1. A connection is established between the UE and the TWAN, using a specific procedure based on IEEE 802.11 [40].

2. The TWAN sends an EAP Request/Identity to the UE.

3. The UE sends an EAP Response/Identity message to the TWAN.

4. The TWAN forwards the EAP payload received from the UE to the 3GPP AAA Server and also indicates the supported TWAN connection modes in the DER message. The routing path may include one or several 3GPP AAA proxies for roaming case.

5. The 3GPP AAA Server retrieves authentication vectors for the UE from the HSS.

6. The 3GPP AAA Server sends an EAP Request/AKA’-Challenge in which it also indicates to the UE the TWAN connection modes supported by the network (e.g. TSCM, SCM and MCM). The Result-Code AVP in the DEA message is set to DIAMETER_MULTI_ROUND_AUTH. The TWAN-S2a-Connectivity Indicator is not set in the DEA-Flags AVP.

7. The TWAN forwards the EAP payload to the UE.

8. The UE sends the EAP Response/AKA’-Challenge. In this example, the UE does not signal any requested connection mode in that message, which indicates a request for TSCM.

9. The TWAN forwards the EAP payload to the 3GPP AAA Server.

10. If the 3GPP AAA Server successfully authentifies the UE, the 3GPP AAA Server downloads the user’s subscription information from the HSS.

11. The 3GPP AAA Server sends an EAP Success message that the TWAN forwards to the UE in step 12 or 16. The Result-Code AVP in the DEA message is set to DIAMETER_SUCCESS. The DEA message also contains the user’s subscription information, whether the user is authorized for EPC and/or non-seamless WLAN offload. The 3GPP AAA Server does not signal any selected TWAN connection mode in the DEA message, which indicates to the TWAN that TSCM is selected.

12. The TWAN forwards the EAP Success message to the UE, when using layer 3 attach trigger.

13. The TWAN sends a Create Session Request/PBU message to the PDN GW to initiate the S2a tunnel establishment (assuming EPC access has been authorized).

14. The PDN GW informs the 3GPP AAA Server/HSS of its PDN GW identity and the APN corresponding to the UE’s PDN Connection.

15. The PDN GW returns a Create Session Response/PBA message to the TWAN, including the IP address(es) allocated for the UE.

16. The TWAN forwards the EAP Success message to the UE, when using layer 2 attach trigger.

Annex B (normative):
Diameter overload control mechanism