15 Functional Description and Procedures for 3GPP Accesses with S2c

23.4023GPPArchitecture enhancements for non-3GPP accessesRelease 18TS

15.1 S2c Bootstrapping via DSMIPv6 Home Link

When connected over the UE home link (i.e. 3GPP access as defined in clause 4.1), the UE may trigger the establishment of S2c IKEv2 SA, e.g. to optimize future handovers to non-3GPP accesses using S2c. For each PDN connection, the S2c IKEv2 SA establishment has to be performed separately.

Figure 15.1-1: S2c PDN Attach via DSMIPv6 home link

0. In this procedure it is assumed that UE is already attached to the PDN over the 3GPP access system as defined in TS 23.401 [4]. This step, according to TS 23.401 [4] could be an initial attach to a default PDN or a UE initiated subsequent attach to another PDN.

1. The UE discovers the PDN GW providing access to the PDN it connected to in Step 0, as defined in the clause 4.5.2. To ensure reachability of the PDN GW, signalling associated with this step as well as step 2 below, should be performed over the connection established by step 0 above.

2. A security association is established between the UE and PDN GW to secure the DSMIPv6 messages related to this PDN connection between the UE and the PDN GW.

The UE initiates the establishment of the security association using IKEv2, RFC 5996 [9]; EAP, RFC 3748 [11] is used over IKEv2 for authentication purposes. The PDN GW communicates with the AAA infrastructure in order to complete the authentication.

During this step an IPv6 home prefix is assigned by the PDN GW to the UE as defined in RFC 4877 [22]. During this step the UE shall include the IPv6 Home Address and may include the APN of the PDN it wants to access. The PDN GW address and APN associated with the UE’s PDN Connectivity are registered by the AAA server with the HSS as described in clause 12.

In this step, the PDN GW may be either in the HPLMN or in the VPLMN. When the PDN GW is in the VPLMN, the interaction between the PDN GW in the VPLMN with the AAA/HSS in the HPLMN may involve a 3GPP AAA Proxy in the VPLMN.

3. UE confirms that it is located in its DSMIPv6 home link for the given PDN, as described for DSMIPv6 Home Link Detection Function in clause 4.5.6.

In some cases this procedure may result in a PDN GW that is different than the one the UE is connected to in step 0. In this case the PDN GW reallocation procedure defined in clause 6.10 is applied.