Radio Link Control

Radio Link Control (RLC) is a layer 2 Radio Link Protocol used in UMTS, LTE and 5G on the Air interface. This protocol is specified by 3GPP in TS 25.322^[1] for UMTS, TS 36.322^[2] for LTE and TS 38.322^[3] for 5G New Radio (NR). RLC is located on top of the 3GPP MAC-layer and below the PDCP-layer. The main tasks of the RLC protocol are:

Transfer of upper layer Protocol Data Units (PDUs) in one of three modes: Acknowledged Mode (AM), Unacknowledged Mode (UM) and Transparent Mode (TM)
Error correction through ARQ (only for AM data transfer)
Concatenation, segmentation and reassembly of RLC SDUs (UM and AM)
Re-segmentation of RLC data PDUs (AM)
Reordering of RLC data PDUs (UM and AM);
Duplicate detection (UM and AM);
RLC SDU discard (UM and AM)
RLC re-establishment
Protocol error detection and recovery

RLC features specific to LTE only - 1) Re-segmentation. 2) RLC SDU discard is notified by upper layer.

References

[1] 3GPP TS 25.322 Radio Link Control (RLC) protocol specification

[2] 3GPP TS 36.322 Evolved Universal Terrestrial Radio Access (E-UTRA); Radio Link Control (RLC) protocol specification

[3] 3GPP TS 38.322 NR; Radio Link Control (RLC) protocol specification

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[2]

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