Content for TS 38.322 Word version: 18.1.0
6 Protocol data units, formats and parameters
6.1 Protocol data units
6.1.1 General
6.1.2 RLC data PDU
6.1.3 RLC control PDU
6.2 Formats and parameters
6.2.1 General
6.2.2 Formats
6.2.2.1 General
6.2.2.2 TMD PDU
6.2.2.3 UMD PDU
6.2.2.4 AMD PDU
6.2.2.5 STATUS PDU
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6 Protocol data units, formats and parameters p. 22
6.1 Protocol data units p. 22
6.1.1 General p. 22
RLC PDUs can be categorized into RLC data PDUs and RLC control PDUs. RLC data PDUs in clause 6.1.2 are used by TM, UM and AM RLC entities to transfer upper layer PDUs (i.e. RLC SDUs). RLC control PDUs in clause 6.1.3 are used by AM RLC entity to perform ARQ procedures.
6.1.2 RLC data PDU p. 22
- TMD PDU TMD PDU is used to transfer upper layer PDUs by a TM RLC entity.
- UMD PDU UMD PDU is used to transfer upper layer PDUs by an UM RLC entity.
- AMD PDU AMD PDU is used to transfer upper layer PDUs by an AM RLC entity.
6.1.3 RLC control PDU p. 22
- STATUS PDU STATUS PDU is used by the receiving side of an AM RLC entity to inform the peer AM RLC entity about RLC data PDUs that are received successfully, and RLC data PDUs that are detected to be lost by the receiving side of an AM RLC entity.
6.2 Formats and parameters p. 22
6.2.1 General p. 22
The formats of RLC PDUs are described in clause 6.2.2 and their parameters are described in clause 6.2.3.
6.2.2 Formats p. 23
6.2.2.1 General p. 23
RLC PDU is a bit string. In the figures in clause 6.2.2.2 to 6.2.2.5, bit strings are represented by tables in which the first and most significant bit is the left most bit of the first line of the table, the last and least significant bit is the rightmost bit of the last line of the table, and more generally the bit string is to be read from left to right and then in the reading order of the lines.
RLC SDUs are bit strings that are byte aligned (i.e. multiple of 8 bits) in length. An RLC SDU is included into an RLC PDU from first bit onward.
6.2.2.2 TMD PDU p. 23
TMD PDU consists only of a Data field and does not consist of any RLC headers.
6.2.2.3 UMD PDU p. 23
UMD PDU consists of a Data field and an UMD PDU header. The UMD PDU header is byte aligned.
When an UMD PDU contains a complete RLC SDU, the UMD PDU header only contains the SI and R fields.
An UM RLC entity is configured by RRC to use either a 6 bit SN or a 12 bit SN. For groupcast and broadcast of NR sidelink communication or for SL-SRB4, only 6 bit SN length is configured. An UMD PDU header contains the SN field only when the corresponding RLC SDU is segmented. An UMD PDU carrying the first segment of an RLC SDU does not carry the SO field in its header. The length of the SO field is 16 bits.
6.2.2.4 AMD PDU p. 24
AMD PDU consists of a Data field and an AMD PDU header. The AMD PDU header is byte aligned.
An AM RLC entity is configured by RRC to use either a 12 bit SN or a 18 bit SN. The length of the AMD PDU header is two and three bytes respectively.
An AMD PDU header contains a D/C, a P, a SI, and a SN. An AMD PDU header contains the SO field only when the Data field consists of an RLC SDU segment which is not the first segment, in which case a 16 bit SO is present.
6.2.2.5 STATUS PDU p. 25
STATUS PDU consists of a STATUS PDU payload and an RLC control PDU header.
RLC control PDU header consists of a D/C and a CPT field.
The STATUS PDU payload starts from the first bit following the RLC control PDU header, and it consists of one ACK_SN and one E1, zero or more sets of a NACK_SN, an E1, an E2 and an E3, and possibly a pair of a SOstart and a SOend or a NACK range field for each NACK_SN.
