EPS and ePDG Interworking for Handover

The following figure illustrates the non-roaming architecture within the EPS using S5 and S2b interfaces.

Non-roaming Architecture Within EPS using S5, S2a, and S2b Interfaces

For 3GPP access to non-3GPP access untrusted Wi-Fi handover and for non-3GPP access untrusted Wi-Fi to 3GPP access handover, if a UE has multiple PDN connections to different APNs in the source access and the UE can route different simultaneously active PDN connections through different access networks, the UE can transfer from the source to the target access all the PDN connections that were active in source access before handover or only a subset of them. This transfer can have the restriction that multiple PDN connections to the same APN have one access.

The transfer process can occur in the following scenarios:

  • 3GPP access to non-3GPP access untrusted Wi-Fi handover

  • Non-3GPP access untrusted Wi-Fi to 3GPP access handover

The UE can transfer from the source to the target access all the PDN connections that were active in source access before handover or only a subset of them if the following conditions are met:

  • The UE has multiple PDN connections to different APNs in the source access

  • The UE can route different, but simultaneously active, PDN connections through different access networks."

The SMF supports untrusted Wi-Fi access for end-users over S2b interface with ePDG after establishment of IPSec connection between the end-user and ePDG.

For untrusted Wi-Fi to EPC handover, the SMF provides a PGW-C FQDN during UDM registration and fetches the subscription information.

During UE handover, the MME fetches PGW-C FQDN from the HSS. After authentication, the MME initiates GTPv2 create session request indicating handover. The SMF+PGW-C does not perform the UDM registration and subscription procedures while processing handover request. SMF+PGW-C ensures that GTPv2 MB request indicating handover is sent to perform data path switching from untrusted Wi-Fi to EPC.

For EPC to untrusted Wi-Fi handover, the HSS provides SMF+PGW-C FQDN after the subscriber authentication. When UE performs handover, after authentication HSS provides SMF+PGW-C FQDN. The ePDG initiates GTPv2 create session request indicating handover toward PGW after IPSec tunnel establishment. SMF+PGW-C performs the UDM registration and no subscription procedures exist while processing the handover request.