6.1.5 MAC PDU (Random Access Response)

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 with RAPID only (i.e. acknowledgment for SI request);

– a MAC subheader with RAPID and MAC RAR.

A MAC subheader with Backoff Indicator consists of five header fields E/T/R/R/BI as described in Figure 6.1.5-1. A MAC subPDU with Backoff Indicator only is placed at the beginning of the MAC PDU, if included. ‘MAC subPDU(s) with RAPID only’ and ‘MAC subPDU(s) with RAPID and MAC RAR’ can be placed anywhere between MAC subPDU with Backoff Indicator only (if any) and padding (if any).

A MAC subheader with RAPID consists of three header fields E/T/RAPID as described in Figure 6.1.5-2.

Padding is placed at the end of the MAC PDU if present. Presence and length of padding is implicit based on TB size, size of MAC subPDU(s).

Figure 6.1.5-1: E/T/R/R/BI MAC subheader

Figure 6.1.5-2: E/T/RAPID MAC subheader

Figure 6.1.5-3: Example of MAC PDU consisting of MAC RARs