Section: 6.1.3.1 Buffer Status Report MAC Control Elements
Content: Buffer Status Report (BSR) MAC control elements consist of either: - Short BSR and Truncated BSR format: one LCG ID field and one corresponding Buffer Size field (figure 6.1.3.1-1); or - Long BSR format: four Buffer Size fields, corresponding to LCG IDs #0 through #3 (figure 6.1.3.1-2). The BSR formats are identified by MAC PDU subheaders with LCIDs as specified in table 6.2.1-2. The fields LCG ID and Buffer Size are defined as follow: - LCG ID: The Logical Channel Group ID field identifies the group of logical channel(s) which buffer status is being reported. The length of the field is 2 bits. For NB-IoT, the LCG ID is set to #0. - Buffer Size: The Buffer Size field identifies the total amount of data available across all logical channels of a logical channel group after all MAC PDUs for the TTI have been built. The amount of data is indicated in number of bytes. It shall include all data that is available for transmission in the RLC layer and in the PDCP layer; the definition of what data shall be considered as available for transmission is specified in TS 36.322[ Evolved Universal Terrestrial Radio Access (E-UTRA); Radio Link Control (RLC) protocol specification ]  [3] and TS 36.323[ Evolved Universal Terrestrial Radio Access (E-UTRA); Packet Data Convergence Protocol (PDCP) specification ]  [4] or TS 38.323[ NR; Packet Data Convergence Protocol (PDCP) specification ]  [17] respectively. The size of the RLC and MAC headers are not considered in the buffer size computation. The length of this field is 6 bits. If extendedBSR-Sizes is not configured, the values taken by the Buffer Size field are shown in Table 6.1.3.1-1. If extendedBSR-Sizes is configured, the values taken by the Buffer Size field are shown in Table 6.1.3.1-2. Figure 6.1.3.1-1: Short BSR and Truncated BSR MAC control element Figure 6.1.3.1-2: Long BSR MAC control element Table 6.1.3.1-1: Buffer size levels for BSR Table 6.1.3.1-2: Extended Buffer size levels for BSR