6.1.5a MAC PDU (MSGB)

38.3213GPPMedium Access Control (MAC) protocol specificationNRRelease 17TS

A MAC PDU consists of one or more MAC subPDUs and optionally padding. Each MAC subPDU consists one of the following:

– a MAC subheader with Backoff Indicator only;

– a MAC subheader and fallbackRAR;

– a MAC subheader and successRAR;

– a MAC subheader and MAC SDU for CCCH or DCCH;

– a MAC subheader and padding.

A MAC subheader with Backoff Indicator consists of five header fields E/T1/T2/R/BI as described in Figure 6.1.5a-1. A MAC subPDU with Backoff Indicator only is placed at the beginning of the MAC PDU, if included.

A MAC subheader for fallbackRAR consists of three header fields E/T1/RAPID as described in Figure 6.1.5a-2. A MAC subheader for successRAR consists of eight header fields E/T1/T2/S/R/R/R/R as described in Figure 6.1.5a-3. A MAC subheader for MAC SDU consists of the four header fields R/F/LCID/L as described in Figure 6.1.2-1 and Figure 6.1.2-2.

At most one ‘MAC subPDU for successRAR’ indicating presence of ‘MAC subPDU(s) for MAC SDU’ is included in a MAC PDU. MAC subPDU(s) for MAC SDU are placed immediately after the ‘MAC subPDU for successRAR’ indicating presence of ‘MAC subPDU(s) for MAC SDU’.

If MAC PDU includes MAC subPDU(s) for MAC SDU, the last MAC subPDU for MAC SDU is placed before MAC subPDU with padding as depicted in Figure 6.1.5a-4. Otherwise, the last MAC subPDU in MAC PDU is placed before padding as depicted in Figure 6.1.5a-5. The MAC subPDU with padding includes R/R/LCID MAC subheader as described in Figure 6.1.2-3 and padding. The size of padding in the MAC subPDU with padding can be zero. The length of padding is implicit based on TB size, size of MAC subPDU(s).

Figure 6.1.5a-1: BI MAC subheader

Figure 6.1.5a-2: FallbackRAR MAC subheader

Figure 6.1.5a-3: SuccessRAR MAC subheader

Figure 6.1.5a-4: Example of a MSGB MAC PDU with MAC SDU(s)

Figure 6.1.5a-5: Example of a MSGB MAC PDU without MAC SDU(s)