Section: 6.1.3.1a Sidelink BSR MAC Control Elements
Content: Sidelink BSR and Truncated Sidelink BSR MAC control elements consist of one Destination Index field, one LCG ID field and one corresponding Buffer Size field per reported target group. The Sidelink BSR MAC control elements are identified by MAC PDU subheaders with LCIDs as specified in table 6.2.1-2. They have variable sizes. For each included group, the fields are defined as follows (figures 6.1.3.1a-1 and 6.1.3.1a-2): - Destination Index: The Destination Index field identifies the ProSe Destination or the destination for V2X sidelink communication. The length of this field is 4 bits. The value is set to the index of the destination reported in destinationInfoList for sidelink communication or is set to one index among index(es) associated to same destination reported in v2x-DestinationInfoList for V2X sidelink communication. If multiple such lists are reported, the value is indexed sequentially across all the lists in the same order as specified in TS 36.331[ Evolved Universal Terrestrial Radio Access (E-UTRA); Radio Resource Control (RRC); Protocol specification ]  [8]; - 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; - Buffer Size: The Buffer Size field identifies the total amount of data available across all logical channels of a LCG of a ProSe Destination 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] 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. The values taken by the Buffer Size field are shown in Table 6.1.3.1-1; - R: Reserved bit, set to "0". Buffer Sizes of LCGs are included in decreasing order of the highest priority of the sidelink logical channel belonging to the LCG irrespective of the value of the Destination Index field. Figure 6.1.3.1a-1: Sidelink BSR and Truncated Sidelink BSR MAC control element for even N Figure 6.1.3.1a-2: Sidelink BSR and Truncated Sidelink BSR MAC control element for odd N