This clause describes a model of the MAC i.e. it does not specify or restrict implementations.
RRC is in control of the MAC configuration.
The MAC entity of the UE handles the following transport channels:
Broadcast Channel (BCH);
Downlink Shared Channel(s) (DL-SCH);
Paging Channel (PCH);
Uplink Shared Channel(s) (UL-SCH);
Random Access Channel(s) (RACH).
When the UE is configured with SCG, two MAC entities are configured to the UE: one for the MCG and one for the SCG.
When the UE is configured with DAPS handover, two MAC entities are used by the UE: one for the source cell (source MAC entity) and one for the target cell (target MAC entity).
The functions of the different MAC entities in the UE operate independently unless otherwise specified. The timers and parameters used in each MAC entity are configured independently unless otherwise specified. The Serving Cells, C-RNTI, radio bearers, logical channels, upper and lower layer entities, LCGs, and HARQ entities considered by each MAC entity refer to those mapped to that MAC entity unless otherwise specified.
If the MAC entity is configured with one or more SCells, there are multiple DL-SCH and there may be multiple UL-SCH as well as multiple RACH per MAC entity; one DL-SCH, one UL-SCH, and one RACH on the SpCell, one DL-SCH, zero or one UL-SCH and zero or one RACH for each SCell.
If the MAC entity is not configured with any SCell, there is one DL-SCH, one UL-SCH, and one RACH per MAC entity.
illustrates one possible structure of the MAC entity when SCG is not configured and for each MAC entity during DAPS handover.
illustrates one possible structure for the MAC entities when MCG and SCG are configured.
In addition, the MAC entity of the UE handles the following transport channel for sidelink:
Sidelink Shared Channel (SL-SCH);
Sidelink Broadcast Channel (SL-BCH).
illustrates one possible structure for the MAC entity when sidelink is configured.