What air interface protocol stacks do 5G base stations support?

5G protocol stack structure

The 5G protocol stack is commonly divided into the following layers:

• Physical layer: Responsible for uplink and downlink data transformation and physical-layer channel scheduling.
• MAC (Medium Access Control) layer: Responsible for frame assembly and segmented transmission, and coordination with the physical layer.
• RLC (Radio Link Control) layer: Responsible for reliable data transfer and segment reassembly, and coordination with the MAC layer.
• PDCP (Packet Data Convergence Protocol) layer: Handles compression, encryption and integrity protection of user data, and coordinates with the RLC layer.
• SDAP (Service Data Adaptation Protocol) layer: Maps different service data to data flows and QoS class parameters.
• RRC (Radio Resource Control) layer: Manages radio resources, including connection establishment, reestablishment, and release, and coordinates across the other layers.

The stack can be adapted or customized for specific functional requirements and deployment scenarios.

Air interface protocols supported by 5G base stations

The air interface protocol stack for a 5G base station typically includes these protocols:

• NR (CU/DU)AP protocol: NR control-plane and user-plane protocol, where CU refers to the control unit and DU refers to the data unit.
• NGAP (Next Generation Application Part) protocol: 5G core network protocol for control-plane entity signaling.
• XnAP (Xn Application Part) protocol: Control signaling between NR cells, supporting full-function link failover and EEA3/EIA3 algorithm configuration.
• E1AP (E1 Application Part) protocol: Control signaling between DUs, supporting flexible cell and PRB-level bandwidth adjustments.
• P5 (Packet Forward Path Protocol) protocol: Controls run-length encoder and supports forward transmission between DUs.
• Uu interface protocol: The radio interface between the UE and the base station, supporting low-latency and high-bandwidth signaling and data.

These protocols form the air interface protocol stack used by base stations to implement the services and functions provided by operators.

Protocols included in 5G Layer 2

Layer 2 of the 5G protocol stack includes the following protocols:

• NR MAC (New Radio Medium Access Control): Implements control logic for the radio access network and coordinates allocation and scheduling of physical-layer resources.
• RLC (Radio Link Control): Provides reliability for data transfer, handles data segmentation and reassembly, and supports both real-time and non-real-time services.
• PDCP (Packet Data Convergence Protocol): Handles header compression and adaptation between higher-layer protocols, and supports encryption and integrity protection.
• SDAP (Service Data Adaptation Protocol): Maps and assigns different service data to data flows and QoS levels, distributing network-layer packets to appropriate data radio bearers.