Radio Link Control

Radio Link Control (RLC) is a layer 2 Radio Link Protocol used in GSM (GPRS), UMTS, LTE and 5G on the Air interface. This protocol is specified by 3GPP in TS 44.060^[1] for GPRS, TS 25.322^[2] for UMTS, TS 36.322^[3] for LTE and TS 38.322^[4] 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] "General Packet Radio Service (GPRS); Mobile Station (MS) - Base Station System (BSS) interface; Radio Link Control / Medium Access Control (RLC/MAC) protocol".

[2] 3GPP TS 25.322 Radio Link Control (RLC) protocol specification

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

[4] 3GPP TS 38.322 NR; Radio Link Control (RLC) protocol specification

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