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Multi-SIM (Rel 17 work area) - Coggle Diagram

- - - - There are some straightforward ways to tackle PO collision, such as monitoring the collision POs in turn, which is UE based solution, or repetition of paging message, which is the network based solution. But these solutions are just to reduce the impact of PO collision and cause the new problem such as paging missing and signaling overhead increasing. Thus, we should consider the UE and the network cooperation to solve this problem, aiming at a better trade-off between network signaling overhead and UE experience.
  - - - Observation 1: The focus of Rel-17 work for concurrent operation is Connected (USIM-A) + Idle/Inactive (USIM-B) modes.
        In the discussion here, per WI scope, we assume that two USIMs will be considered as two separate UEs by the NW and the NW is not aware of the co-location of two USIMs in a single physical device. In addition, any optimizations for intra-PLMN case (when both USIMs belong to the same operator) are excluded.
      - Observation 2: Two USIMs are considered as two independent and separate UEs from NW perspective
        
        Scenario 1: 1. UE needs to switch to USIM-B for short-term activity without losing the connection in USIM-A. This can be to listen to paging and also possibly other short-term activities such as TAU and RNAU.
        
        Scenario 2: 2. UE is not able to monitor paging on USIM-B for a long term duration , for example when making a voice call on USIM-A. This scenario can also occur if USIM-B starts in Connected mode and USIM-A in Idle mode and the UE has to move to Connected mode in USIM-A by leaving USIM-B.
        
        NOTE 1: Any privacy implications of implicitly indicating to the MNO owning one USIM that the UE is also using another USIM (potentially owned by another MNO) will be studied by SA WG3.
        NOTE 2: For this key issue, coordination with RAN WGs WGs is needed for final solution decision. No E-UTRA radio interface impact is expected in RAN WGs.
        
        Proposal 1: The Uu procedures to enable switching between two SIMs should only impact NR specifications.
        For the first scenario, if the UE leaves USIM-A connection without informing the gNB (e.g. to listen to paging on the other USIM), there will be a disruption to its communication; for example, it will not be able to receive DL PDUs or send any UL signals. This is not an expected behavior from system point of view. Therefore, any such disruption should be coordinated with the gNB in advance.
      - Observation 3: The UE suspending DL and UL activity by itself in RRC Connected mode is not compliant with current specifications and thus will be considered an error case.
        
        Proposal 2: The UE should coordinate with gNB any upcoming suspension of DL and UL transmission (due to activity on another link) when it is in RRC Connected mode.