6.10 PDN GW reallocation upon attach on S2c

23.4023GPPArchitecture enhancements for non-3GPP accessesRelease 18TS

The PDN GW reallocation procedure depicted in figure 6.10-1 can be used by the HSS/AAA to force the assignment of a new PDN GW to the UE upon attach with DSMIPv6 in a trusted or untrusted non-3GPP IP access. The decision on whether to trigger PDN GW reallocation is taken by the HSS/AAA according to the principles described in clause 4.5.2.

Figure 6.10-1: PDN GW reallocation upon attach on S2c

The following is a detailed description of the involved steps:

1) The UE authenticates in the trusted non-3GPP access, or establishes the IPsec tunnel with the ePDG, and obtains a local IP address to be used as care-of address for DSMIPv6.

2) The UE establishes the DSMIPv6 SA with the initially discovered PDN GW. This implies an AAA exchange with the HSS/AAA. The HSS/AAA triggers the reallocation of the PDN GW and the APN associated with the UE’s PDN Connection by piggybacking a reallocation indication and the target PDN GW identity in the AAA exchange. In the signalling from the PDN-GW to the UE, the PDN-GW indicates reallocation, assigns no IPv6 prefix to the UE and includes the IP address of the target PDN GW.

If the target PDN GW identity is stored in the HSS in form of the IP address, then this IP address can be transferred to the UE directly. If the target PDN GW identity is stored in the HSS in form of the PDN GW FQDN, the initial PDN GW shall derive the IP address of the HA functionality of the target PDN GW from the PDN GW FQDN provided by the AAA server and provide it to the UE.

3) The UE establishes the DSMIPv6 SA with the target PDN GW provided by the network during step 2.

4) The UE performs the DSMIPv6 registration with the target PDN GW.

NOTE 1: In case the UE performs DSMIPv6 bootstrapping for an existing PDN connection, the UE includes its IPv6 Home Address during step 2.

NOTE 2: The DSMIPv6 SA between the UE and the initial PDN GW may be implicitly removed by the UE and the initial PDN GW any time after step 2, before expiry of the SA.