SSC: Session and Service Continuity Mode
SSC is used to support multiple continuity requirements.
SSC is associated with PDU session and will not change during the lifespan of a PDU session.
It means, if a PDU connection is set to SSC mode-x, then it will not be changed until the PDU session is deactivated.
During session establishment of a PDU session, a PDU Session Anchor(PSA) is selected that remains as the IP anchor point.
So, when a UE is moving around the network, it is possible that the original PSA is not optimal.
This will result in new IP address allocation to the UE. So some applications that do not sit well with the IP address change, there might raise some issues.
SSC mode determines how UPF of a PDU session is allocated.
There are 3 SSC modes in 5GS.
SSC Mode 1:
Network preserves the connectivity service provided to the UE. PDU session and IP address is preserved throughout lifetime of UE mobility.
Here the PDU session anchor UPF is maintained throughout session lifetime.
SSC Mode 2:
In this mode, the network may release the connectivity to UE and may also release PDU session.
In this case, the IP address will be changed during re-allocation.
If a new PDU session is established, then a new anchor UPF will be created.
SSC Mode 3:
In this mode, network make sure to provide no connectivity loss to UE. If a new PDU session is required, then a new PDU session anchor point is established before the previous connection is terminated.
This will help in better service continuity.
Reference: TS23.501