5G NR RLC (Radio Link Control)


  • RLC stands for Radio Link Control Protocol.
  • It is a layer of 5G NR radio protocol stack.
  • It is placed top of the MAC Layer and below of the PDCP layer (for user plane) or RRC layer (for control plane) in the Radio Protocol Stack in 5G NR.

Transmissions Modes :

  • Transparent Mode (TM)
  • Unacknowledged Mode (UM)
  • Acknowledged Mode (AM)

The main services and functions of the RLC sub-layer depend on the transmission mode and include:

  • Transfer of upper layer PDUs
  • Sequence numbering independent of the one in PDCP (UM and AM)
  • Error Correction through ARQ (AM only)
  • Segmentation (AM and UM) and re-segmentation (AM only) of RLC SDUs
  • Reassembly of SDU (AM and UM)
  • Duplicate Detection (AM only)
  • RLC SDU discard (AM and UM)
  • RLC re-establishment
  • Protocol error detection (AM only)


  • ARQ retransmits RLC SDUs or RLC SDU segments based on RLC status reports;
  • Polling for RLC status report is used when needed by RLC;
  • RLC receiver can also trigger RLC status report after detecting a missing RLC SDU or RLC SDU segment.

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Reference :

3GPP TS 38.300 Rel 15 Ver 15.3.0

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