Content for  TS 38.300  Word version:  16.3.0

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6  Layer 2Word‑p. 39

6.1  Overview

The layer 2 of NR is split into the following sublayers: Medium Access Control (MAC), Radio Link Control (RLC), Packet Data Convergence Protocol (PDCP) and Service Data Adaptation Protocol (SDAP). The two figures below depict the Layer 2 architecture for downlink and uplink, where:
  • The physical layer offers to the MAC sublayer transport channels;
  • The MAC sublayer offers to the RLC sublayer logical channels;
  • The RLC sublayer offers to the PDCP sublayer RLC channels;
  • The PDCP sublayer offers to the SDAP sublayer radio bearers;
  • The SDAP sublayer offers to 5GC QoS flows;
  • Comp. refers to header compression and segm. to segmentation;
  • Control channels (BCCH, PCCH are not depicted for clarity).
Reproduction of 3GPP TS 38.300, Figure 6.1-1: Downlink Layer 2 Structure
Reproduction of 3GPP TS 38.300, Figure 6.1-2: Uplink Layer 2 Structure
Radio bearers are categorized into two groups: data radio bearers (DRB) for user plane data and signalling radio bearers (SRB) for control plane data.
For IAB, the Layer 2 of NR also includes: Backhaul Adaptation Protocol (BAP).
  • The BAP sublayer supports routing across the IAB topology and traffic mapping to BH RLC channels for enforcement of traffic prioritization and QoS.
Figure 6.1-3 below depicts the Layer-2 architecture for downlink on the IAB-donor. Figures 6.1-4 and 6.1-5 depict the Layer-2 architecture for downlink and uplink on the IAB-node, where the BAP sublayer offers routing functionality and mapping to BH RLC channels.
Reproduction of 3GPP TS 38.300, Figure 6.1-3: DL L2-structure for user plane at IAB-donor
Reproduction of 3GPP TS 38.300, Figure 6.1-4: DL L2-structure at IAB-node
Reproduction of 3GPP TS 38.300, Figure 6.1-5: UL L2-structure at IAB-node

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