6.1.2 MAC PDU (DL-SCH and UL-SCH except transparent MAC and Random Access Response)

38.3213GPPMedium Access Control (MAC) protocol specificationNRRelease 17TS

A MAC PDU consists of 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 corresponds to either a MAC SDU, a MAC CE, or padding.

A MAC subheader except for fixed sized MAC CE, padding, and a MAC SDU containing UL CCCH consists of the header fields R/F/LCID/(eLCID)/L. A MAC subheader for fixed sized MAC CE, padding, and a MAC SDU containing UL CCCH consists of the two header fields R/LCID/(eLCID).

Figure 6.1.2-1: R/F/LCID/(eLCID)/L MAC subheader with 8-bit L field

Figure 6.1.2-2: R/F/LCID/(eLCID)/L MAC subheader with 16-bit L field

Figure 6.1.2-3: R/LCID/(eLCID) MAC subheader

MAC CEs are placed together. DL MAC subPDU(s) with MAC CE(s) is placed before any MAC subPDU with MAC SDU and MAC subPDU with padding as depicted in Figure 6.1.2-4. UL MAC subPDU(s) with MAC CE(s) 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 6.1.2-5. The size of padding can be zero.

Figure 6.1.2-4: Example of a DL MAC PDU

Figure 6.1.2-5: Example of a UL MAC PDU

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