Section: 20.3 UE notification on Network Switching
Content: For MUSIM operation, a MUSIM device in RRC_CONNECTED state in Network A may have to switch from Network A to Network B. Network A is NR and Network B can either be E-UTRA or NR. Before switching from Network A, a MUSIM device should notify Network A to either leave RRC_CONNECTED state, or be kept in RRC_CONNECTED state in Network A while temporarily switching to Network B. When configured to do so, a MUSIM device can signal to the Network A a preference to leave RRC_CONNECTED state by using RRC (see TS 38.331[ NR; Radio Resource Control (RRC); Protocol specification ]  [12]) or NAS signalling (see TS 23.501[ System architecture for the 5G System (5GS) ]  [3]). After sending a preference to leave RRC_CONNECTED state by using RRC signalling, if the MUSIM device does not receive an RRCRelease message from the Network A within a certain time period (configured by the Network A, see TS 38.331[ NR; Radio Resource Control (RRC); Protocol specification ]  [12]), the MUSIM device can enter RRC_IDLE state in Network A. When configured to do so, a MUSIM device can signal to the Network A a preference to be temporarily switching to Network B while remaining in RRC_CONNECTED state in Network. This is indicated by scheduling gaps preference. This preference can include information for setup or release of gap(s). The Network A can configure at most 4 gap patterns for MUSIM purpose: three periodic gaps and a single aperiodic gap. The Network A should always provide at least one of the requested gap pattern or no gaps. Network providing an alternative gap pattern instead of the one requested by the UE is not supported in this release. When configured to do so, a MUSIM device can include priority of periodic gap(s) in addition to scheduling gaps preference, and the priority preference should be indicated for all periodic gap(s). If the MUSIM device indicates gap priority preference, it can also indicate its preference on using keep solution (defined in TS 38.133[ NR; Requirements for support of radio resource management ] [13]).