16.10.5.3.5 Service Continuity in RRC_INACTIVE

Mobility procedures for multicast reception allow the UE in RRC_INACTIVE state to continue receiving MBS service(s) when changing cells without resuming RRC connection if the PTM configuration of the new cell can be acquired by the UE from the multicast MCCH after cell reselection. During an active MBS multicast session, the UE is required to resume RRC connection to get the PTM configuration if the PTM configuration or multicast MCCH is not provided in the new cell. Even if the UE in RRC_INACTIVE state has received an indication to stop monitoring PDCCH addressed by G-RNTI for an MBS multicast session in the source cell, the UE acquires multicast MCCH in the reselected cell after cell reselection.

The gNB may indicate in the multicast MCCH the list of neighbour cells providing the same MBS multicast service(s) for UEs in RRC_INACTIVE state as provided in the serving cell. This allows the UE, e.g., to resume RRC connection without reading SIB24 and multicast MCCH of the neighbour cell, if the interested service which is activated is not available to the UE in RRC_INACTIVE state.

The gNB may provide an indication on cell PDCP COUNT synchronization for an MBS session with PTM configuration in RRCRelease message. If indicated by the gNB, all cells within the RNA are synchronized in terms of PDCP COUNT value to the MRBs of the corresponding MBS service, and the order of MRBs within the list of multicast MRB configuration for the same MBS multicast session in the multicast MCCH message of the last serving cell and (re)selected cell within the RNA should be consistent. Upon reselection to a cell indicated as synchronized in terms of PDCP COUNT value, the UE does not initialize the PDCP state variables. Otherwise, the UE initializes the PDCP state variables as defined in TS 38.323 [8].

The UE may be configured with dedicated frequency priorities in RRCRelease message which the UE applies during cell reselection while receiving data of MBS multicast session in RRC_INACTIVE state.

The UE receiving multicast session(s) in RRC_INACTIVE state triggers RRC connection resumption if the latest measured RSRP or RSRQ of the serving cell becomes lower than the threshold configured by the network. The threshold can be configured per MBS session via RRCRelease message or multicast MCCH.