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5G NR Radio Protocol Stack (Layer 2 and Layer 3)

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5G NR (New Radio) is the latest generation of mobile communication standards, and its protocol stack has evolved to meet the demands of higher data rates, lower latency, and massive connectivity. The 5G NR protocol stack is defined by 3GPP (3rd Generation Partnership Project), the organization responsible for standardizing cellular systems.

Let's delve into the technical details of the 5G NR protocol stack, focusing on Layer 2 (Data Link Layer) and Layer 3 (Network Layer).

5G NR Protocol Stack Overview:

The 5G NR protocol stack can be conceptualized in three main layers:

  1. Layer 1 (Physical Layer): Handles the physical transmission and reception of data over the air interface.
  2. Layer 2 (Data Link Layer): Manages data framing, error control, and some aspects of multiplexing.
  3. Layer 3 (Network Layer): Manages end-to-end communication, routing, and mobility functions.

The Data Link Layer in 5G NR is responsible for:

  1. Error Control: Ensures data integrity using mechanisms like Automatic Repeat reQuest (ARQ).
  2. Data Framing: Divides the data stream into frames, and performs functions like segmentation and reassembly.
  3. Logical Channel Multiplexing: Multiplexes different types of data and control information onto transport channels.

The Layer 2 in 5G NR is further divided into:

  1. MAC (Medium Access Control) Layer:
    • Responsible for multiplexing/demultiplexing of logical channels onto transport channels.
    • Handles prioritization and scheduling of data for transmission.
    • Supports various functionalities like HARQ (Hybrid Automatic Repeat Request) for error correction.
  2. RLC (Radio Link Control) Layer:
    • Provides reliable transmission of data between the UE (User Equipment) and gNB (5G NodeB).
    • Supports three modes of operation: Transparent Mode, Unacknowledged Mode, and Acknowledged Mode.
    • Performs segmentation and reassembly of RLC SDUs (Service Data Units).

Layer 3 (Network Layer):

The Network Layer in 5G NR is responsible for:

  1. Mobility Management: Handles UE registration, authentication, and mobility procedures like handovers.
  2. Session Management: Manages user sessions, establishment, modification, and release of data sessions.
  3. RRC (Radio Resource Control) Protocol:
    • Establishes, configures, and releases radio bearers.
    • Manages radio resources and controls the connection between UE and gNB.
    • Handles procedures like connection establishment, reconfiguration, and release.

The RRC protocol states include:

  • Idle State: UE is not actively communicating.
  • Connected State: UE is connected to the network and can send/receive data.

Key Aspects:

  1. PDU Sessions: In 5G, a new concept called the PDU (Packet Data Unit) session has been introduced. It enables efficient handling of data sessions, independent of the underlying access technology.
  2. Network Slicing: 5G NR supports network slicing, allowing operators to create multiple virtual networks on a single physical infrastructure, each tailored to specific requirements like latency, bandwidth, and reliability.
  3. Dual Connectivity: Enables simultaneous connection to both 4G and 5G networks, providing enhanced data rates and seamless mobility.