Content for  TS 38.331  Word version:  18.0.0

UE configured to receive MBS multicast service(s) in RRC_INACTIVE that the UE has joined applies MBS multicast procedures described in this clause. MBS multicast configuration information is provided in RRCRelease and on multicast MCCH logical channel. When there is temporarily no data for an active multicast session or when the multicast session is deactivated, the network notifies the UE to stop monitoring the corresponding G-RNTI via MBS multicast configuration information. If the UE is notified to stop monitoring the G-RNTI(s) for all the joined multicast sessions, it stops monitoring the Multicast MCCH-RNTI for the cell where it received the notification. Multicast MCCH carries the MBSMulticastConfiguration message which indicates the MBS multicast sessions that are provided in the cell as well as the corresponding scheduling related information for these sessions. Optionally, the MBSMulticastConfiguration message may also contain a list of neighbour cells providing the same MBS multicast service(s) for RRC_INACTIVE as provided in the current cell. The configuration information required by the UE to receive multicast MCCH is provided in SIB24.

The multicast MCCH information (i.e. information transmitted in messages sent over multicast MCCH) is transmitted periodically, using a configurable repetition period and within a configured transmission window. MCCH transmissions (and the associated radio resources and MCS) are indicated via the PDCCH addressed to Multicast MCCH-RNTI. PDCCH monitoring occasion(s) for the multicast MCCH transmission are determined according to the common search space indicated by searchspaceMulticastMCCH. If searchspaceMulticastMCCH is set to zero, PDCCH monitoring occasions for the multicast MCCH message reception in the multicast MCCH transmission window are the same as PDCCH monitoring occasions for SIB1 where the mapping between PDCCH monitoring occasions and SSBs is specified in TS 38.213. If searchspaceMulticastMCCH is not set to zero, PDCCH monitoring occasions for the multicast MCCH message are determined based on search space indicated by searchspaceMulticastMCCH. PDCCH monitoring occasions for the multicast MCCH message which are not overlapping with UL symbols (determined according to tdd-UL-DL-ConfigurationCommon) are sequentially numbered from one in the multicast MCCH transmission window. The [x×N+K]th PDCCH monitoring occasion for the multicast MCCH message in the multicast MCCH transmission window corresponds to the Kth transmitted SSB, where x = 0, 1, ...X-1, K = 1, 2, …N, N is the number of actual transmitted SSBs determined according to ssb-PositionsInBurst in SIB1 and X is equal to CEIL(number of PDCCH monitoring occasions in multicast MCCH transmission window/N). The actual transmitted SSBs are sequentially numbered from one in ascending order of their SSB indexes. The UE assumes that, in the multicast MCCH transmission window, PDCCH for a multicast MCCH message is transmitted in at least one PDCCH monitoring occasion corresponding to each transmitted SSB and thus the selection of SSB for the reception multicast MCCH messages is up to UE implementation.

Change of multicast MCCH information only occurs at specific radio frames, i.e. the concept of a modification period is used. Within a modification period, the same multicast MCCH information may be transmitted a number of times, as defined by its scheduling (which is based on a repetition period). When the network changes (some of) the multicast MCCH information, it notifies the UEs about the change starting from the beginning of the multicast MCCH modification period via PDCCH which schedules the multicast MCCH in every repetition in that modification period. Upon receiving a change notification, a UE receiving MBS multicast service(s) in RRC_INACTIVE acquires the new multicast MCCH information starting from the same slot. The UE applies the previously acquired multicast MCCH information until the UE acquires the new multicast MCCH information.

The UE applies the multicast MCCH information acquisition procedure to acquire the MBS multicast configuration information from the network. The procedure applies to UEs configured to receive MBS multicast services in RRC_INACTIVE.

If configured to receive MBS multicast services in RRC_INACTIVE, a UE applies the multicast MCCH information acquisition procedure for PTM configuration update and upon reselection to a new cell providing SIB24. A UE that is receiving MBS multicast data in RRC_INACTIVE shall apply the multicast MCCH information acquisition procedure upon receiving a notification that the multicast MCCH information has changed. Unless explicitly stated otherwise in the procedural specification, the multicast MCCH information acquisition procedure overwrites any stored multicast MCCH information, i.e. delta configuration is not applicable for multicast MCCH information and the UE discontinues using a field if it is absent in multicast MCCH information.

A UE configured to receive an MBS multicast service in RRC_INACTIVE shall:

No UE requirements related to the contents of the MBSMulticastConfiguration message apply other than those specified elsewhere, e.g., within the corresponding field descriptions.

The multicast MRB configuration procedure is used by the UE in RRC_INACTIVE state to configure PDCP, RLC, MAC entities and the physical layer upon PTM configuration update and moving to a cell providing SIB24. The UE may perform multicast MRB modification or release/establishment when PTM configuration is updated via MCCH or when it moves to a cell where the PDCP COUNT of the corresponding multicast MRB is not synchronized within the RNA. The UE may perform multicast MRB modification when it moves to a cell where the PDCP COUNT of the corresponding multicast MRB is synchronized within the RNA. The UE resets MAC upon cell-reselection. Upon moving to a cell where the PDCP COUNT of a multicast MRB is not synchronized, an indication is sent to the lower layer to inform the PDCP COUNT non-synchronization of the corresponding multicast MRB. Upon transition from RRC_CONNECTED to RRC_INACTIVE in the same cell, the UE can continue using the multicast MRBs used in RRC_CONNECTED.

Upon establishment of a multicast MRB, the UE shall:

Upon release of a multicast MRB, the UE shall: