6.1.6 MAC PDU (SL-SCH)

38.3213GPPMedium Access Control (MAC) protocol specificationNRRelease 17TS

A MAC PDU consists of one SL-SCH subheader and one or more MAC subPDUs. Each MAC subPDU consists of one of the following:

– A MAC subheader only (including padding);

– A MAC subheader and a MAC SDU;

– A MAC subheader and a MAC CE;

– A MAC subheader and padding.

The MAC SDUs are of variable sizes.

Each MAC subheader except SL-SCH subheader corresponds to either a MAC SDU, a MAC CE, or padding.

The SL-SCH subheader is of a fixed size and consists of the seven header fields V/R/R/R/R/SRC/DST.

Figure 6.1.6-1: SL-SCH MAC subheader

A MAC subheader except for fixed-sized MAC CE and padding consists of the four header fields R/F/LCID/L as depicted in Figure 6.1.2-1 (with 8-bit L field) and Figure 6.1.2-2 (with 16-bit L field). A MAC subheader for fixed-sized MAC CE and padding consists of the two header fields R/LCID as depicted in Figure 6.1.2-3.

SL MAC subPDU(s) with MAC SDU(s) is placed after the SL-SCH subheader and before the MAC subPDU with a MAC CE and the MAC subPDU with padding in the MAC PDU as depicted in Figure 6.1.6-2. SL MAC subPDU with a MAC CE is placed after all the MAC subPDU(s) with MAC SDU and before the MAC subPDU with padding in the MAC PDU as depicted in Figure 6.1.6-2. The size of padding can be zero.

Figure 6.1.6-2: Example of an SL MAC PDU

A maximum of one MAC PDU can be transmitted per TB per MAC entity.