What is the purpose of the Layer 3 protocol in 5G (NR)?

Ⅰ、Protocols are the rules and standards that define how data is connected, transmitted and managed over a network. In the field of communications protocols ensure that hardware and software operate harmoniously across different end-user devices (UEs) and infrastructures, and they control everything from the formation, transmission and reception of packets to the safe and efficient connection and communication of devices.

Ⅱ、Why protocols are needed this is because of the following reasons;

• Interoperability:Protocols standardize the communication between different systems and devices, ensuring that they can interact with information (signaling) without discrimination.
• System Efficiency:Optimized protocols make better use of network resources, reduce costs and improve quality of service.
• System Security: Protocols incorporate security measures to protect the integrity, confidentiality and authenticity of data.
• Scalability: Standardized protocols support the expansion of network functions without requiring major changes to the core network structure.

Ⅲ、The protocol layering in the 5G (NR) network system its protocol structure for layered management, commonly used layer three architecture for the L1, L2 and L3 layers. This structure helps modular organization of network functions, simplifies the design, implementation and troubleshooting; the role of each layer is as follows:

3.1 L1 (Physical Layer)

• Purpose:The physical layer is responsible for transmitting and receiving raw bit streams over physical media, specifically converting digital bits into signals and vice versa.

• Physical layer 5G functions mainly include:​

❶ Waveform Generation:The use of OFDM (Orthogonal Frequency Division Multiplexing) enables efficient and interference-resistant high-speed data transmission.
❷ Modulation and demodulation: Determine the signal formation method and modulation scheme (e.g. QPSK, QAM) according to the network conditions.
❸ Data error correction: techniques such as forward error correction are used to improve data integrity without retransmission.

3.2 L2 (Data Link Layer)

• Purpose:The data link layer ensures that data is transmitted reliably over the physical network, allows data to be organized into frames and detects/resolves errors that occur at the physical layer.

• 5G Data Link Sublayer:

❶ MAC (Media Access Control): Manages and maintains control of the radio channel and multiplexes data streams from various sources.

❷ RLC (Radio Link Control): Enhances reliability by segmenting and reorganizing packets, and manages error correction through ARQ (Automatic Repeat Request).

❸ PDCP (Packet Data Convergence Protocol): compresses headers and provides encryption and integrity checking to ensure the security of user data.

3.3 L3 (Network Layer)

• Purpose: The network layer is responsible for transmitting packets from the source host to the destination host based on the address of the packet. It defines the path taken by the packet from the sender to the receiver.
• Key Functions in 5G：

❶ IP Routing and Transport: Manages packet forwarding, including addressing, routing, and flow control.
❷ Session Management: Manages the setup and maintenance of network connections.
❸ Mobility Management: Handles the operations required to move devices between sectors or networks while maintaining ongoing sessions.