5.6.9.2.3 SSC Mode 3

For PDU Session of SSC mode 3, the network allows the establishment of UE connectivity via a new PDU Session Anchor to the same data network before connectivity between the UE and the previous PDU Session Anchor is released. When trigger conditions apply, the network decides whether to select a PDU Session Anchor UPF suitable for the UE's new conditions (e.g. point of attachment to the network).

In this Release of specification, SSC mode 3 only applies to IP PDU Session type and to any access type.

In the case of a PDU Session of IPv4 or IPv6 or IPv4v6 type, during the procedure of change of PDU Session Anchor, the following applies:

a. For a PDU Session of IPv6 type, the new IP prefix anchored on the new PDU Session Anchor may be allocated within the same PDU Session (relying on IPv6 multi-homing specified in clause 5.6.4.3), or

b. The new IP address and/or IP prefix may be allocated within a new PDU Session that the UE is triggered to establish.

After the new IP address/prefix has been allocated, the old IP address/prefix is maintained during some time indicated to the UE via NAS signalling (as described in clause 4.3.5.2 of TS 23.502 [3]) or via Router Advertisement (as described in clause 4.3.5.3 of TS 23.502 [3]) and then released.

If a PDU Session of SSC mode 3 has multiple PDU Session Anchors (i.e. in the case of multi-homed PDU Sessions or in the case that UL CL applies to a PDU Session of SSC mode 3), the additional PDU Session Anchors may be released or allocated.

SSC mode 3 is optional to be supported in the UE.

NOTE: Features depending on SSC mode 3 will not work with the lack of support for SSC mode 3 in the UE.