9.1 Protocol data units

25.3223GPPRadio Link Control (RLC) protocol specificationRelease 17TS

Tools: ARFCN - Frequency Conversion for 5G NR/LTE/UMTS/GSM

The structures defined in this subclause are normative.

9.1.1 Data PDUs

a) TMD PDU (Transparent Mode Data PDU).

The TMD PDU is used to convey RLC SDU data without adding any RLC overhead. The TMD PDU is used by RLC when it is in transparent mode.

b) UMD PDU (Unacknowledged Mode Data PDU).

The UMD PDU is used to convey sequentially numbered PDUs containing RLC SDU data. UMD PDUs are used by RLC when it is configured for unacknowledged data transfer.

c) AMD PDU (Acknowledged Mode Data PDU).

The AMD PDU is used to convey sequentially numbered PDUs containing RLC SDU data. AMD PDUs are used by RLC when it is configured for acknowledged data transfer.

9.1.2 Control PDUs

Control PDUs are only used in acknowledged mode.

a) STATUS PDU and Piggybacked STATUS PDU.

The STATUS PDU and the Piggybacked STATUS PDU are used:

– by the Receiver to inform the Sender about missing and received AMD PDUs in the Receiver;

– by the Receiver to inform the Sender about the size of the allowed transmission window;

– by the Sender to request the Receiver to move the reception window; and

– by the Receiver to acknowledge the Sender about the reception of the request to move the reception window.

b) RESET PDU.

The RESET PDU is used to reset all protocol states, protocol variables and protocol timers of the peer RLC entity in order to synchronise the two peer entities. It is sent by the Sender to the Receiver.

c) RESET ACK PDU.

The RESET ACK PDU is an acknowledgement to the RESET PDU. It is sent by the Receiver to the Sender.

Table 9.1: RLC PDU names and descriptions

Data Transfer Mode	PDU name	Description
Transparent	TMD	Transparent mode data
Unacknowledged	UMD	Sequenced unacknowledged mode data
Acknowledged	AMD	Sequenced acknowledged mode data
	STATUS	Solicited or Unsolicited Status Report, Change window size command, SDU discard command, or SDU discard acknowledgement
	Piggybacked STATUS	Piggybacked Solicited or Unsolicited Status Report, Change window size command, SDU discard command, or SDU discard acknowledgement
	RESET	Reset Command
	RESET ACK	Reset Acknowledgement