5G-NR Protocol Stack | Layer 1|Layer 2|Layer 3

The 5G New Radio (NR) protocol stack efficiently handles both signaling messages and user data, each taking its own dedicated path.

Think of it like a highway with two lanes:

Lane 1: Control Plane (C-Plane)

Handles signaling messages related to network access, mobility management, and service control.

Think of it as the lane used for traffic signals, directions, and managing vehicle flow.

Key layers

• Radio Resource Control (RRC): Negotiates radio resources and manages cell handovers.
• Non-Access Stratum (NAS): Provides overall system access and mobility control.
• Access and Mobility Management Function (AMF): The central control unit for signaling messages.

Lane 2: User Plane (U-Plane)

Carries user data like video calls, web browsing, and file transfers.

Think of it as the lane carrying the actual data passengers.

Key layers

• Service Data Adaptation Protocol (SDAP): Optimizes user data for efficient transmission.
• User Plane Function (UPF): Handles user data processing and forwarding.

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Shared Infrastructure, Different Destinations:

Both C-Plane and U-Plane share the foundation of the protocol stack, including:

• Physical Layer (PHY): Converts data into radio signals and vice versa.
• Medium Access Control (MAC): Manages access to the radio channel.
• Radio Link Control (RLC): Ensures reliable data delivery.
• Packet Data Convergence Protocol (PDCP): Prepares data for transmission.

However, they diverge at the top, with C-Plane connecting to AMF and U-Plane connecting to UPF, serving their distinct purposes.

RRC Layer (Radio Resource Control) of 5G-NR |Layer 3

The 5G RRC layer, residing within the network layer (Layer 3), plays a critical role in the magic of 5G communication. But what exactly does it do? Think of it as the brains behind the scenes, constantly ensuring your calls connect, data flows smoothly, and you stay seamlessly connected even on the move.

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Here's a breakdown of its key functions, with some added insights:

1.????? Setting the Stage: Broadcasting System Information

The RRC layer broadcasts essential network information to both the Non-Access Stratum (NAS) and Access Stratum (AS), acting as a shared knowledge base for efficient communication.

2.????? Connection Central: Establishing, Maintaining, and Releasing RRC Connections

Just like handshaking before a conversation, the RRC layer establishes and maintains the connection between your device and the network (gNB). It manages the initial setup, ensuring smooth authentication and authorization, and handles disconnections gracefully when needed.

3.????? Security First: Key Management and Protection

Security is paramount in 5G, and the RRC layer plays a crucial role in ensuring it. It handles key management, generating and exchanging encryption keys so your data travels securely, protected from eavesdropping or tampering.

4.????? Building Data Highways: Establishing and Managing Radio Bearers

Imagine dedicated lanes on a highway for different types of traffic. Similarly, the RRC layer establishes and manages "radio bearers" – dedicated data channels tailored to specific needs. It configures, maintains, and releases these bearers, ensuring optimal resource allocation and data flow for voice calls, video streaming, or internet browsing.

5.????? Keeping You Connected: Mobility Functions and Cell Management

As you move across different cell zones, the RRC layer orchestrates seamless handovers, ensuring uninterrupted connectivity. It manages cell addition and release based on traffic demands, keeping your device connected to the optimal cell for the best possible experience.

6.????? Measurement and Reporting: Keeping the Network Informed

Your device constantly measures signal strength, quality, and surrounding cell information. The RRC layer facilitates this reporting, providing valuable insights to the network for optimizing performance and resource allocation. It also controls this reporting frequency to avoid unnecessary overhead.

7.????? Direct Communication Channel: NAS Message Transfer

The RRC layer acts as a bridge between the NAS layer, responsible for overall system access and mobility control, and your device. It facilitates the direct transfer of NAS messages, ensuring efficient communication and control signaling.

8.????? Deeper Dive: Exploring the Resources

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For a more intricate understanding, refer to the provided resources on 5G NR UE RRC States and RRC Information Elements. These delve deeper into the technical details and specifications that make the RRC layer function.

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MAC, RLC, PDCP, SDAP of 5G-NR |Layer 2

Media Access Control (MAC) layer

The 5G Media Access Control (MAC) layer, residing in Layer 2, plays a pivotal role in managing radio resources and ensuring efficient communication. Here are some key pointers to understand its functions:

1.????? Beam Management: Directs radio signals towards your device for improved performance.

2.????? Random Access Procedure: Enables your device to efficiently join the network.

3.????? Mapping and Multiplexing: Translates different data types and combines them for efficient transmission.

4.????? Scheduling: Determines which devices transmit when, optimizing resource allocation.

5.????? HARQ Error Correction: Ensures reliable data delivery by retransmitting lost packets.

6.????? Priority Handling: Prioritizes critical data (e.g., voice calls) for a seamless experience.

7.????? Transport Format Selection: Chooses the most efficient way to pack data based on channel conditions.

8.????? Padding: Adjusts data size to match transmission requirements, further optimizing resource utilization.

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Radio Link Control (RLC) Layer

The Radio Link Control (RLC) sublayer, residing in Layer 2, bridges the gap between upper layer data and the MAC layer, ensuring reliable and efficient delivery over the air interface. Here's a summary of its key functions:

1.????? Transfers Data: Carries data packets received from upper layers towards the MAC.

2.????? Corrects Errors (AM mode only): Re-transmits lost or corrupted data packets for guaranteed delivery.

3.????? Reorders Data (UM & AM modes): Ensures data arrives in the correct order, even after retransmissions.

4.????? Detects Duplicates (UM & AM modes): Prevents redundant data delivery.

5.????? Manages Buffers: Optimizes data flow to avoid overwhelming the MAC layer.

6.????? Adapts to Needs: Operates in different modes (TM, UM, AM) based on data type and reliability requirements.

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Packet Data Convergence Protocol (PDCP) Layer

The Packet Data Convergence Protocol (PDCP) layer, residing in Layer 2, plays a crucial role in securing and streamlining user plane (UP) data transmission in 5G networks. Here's a summary of its key functions:

1.????? Transfer of User Data: Carries all types of user data (voice, video, browsing, etc.) over the air interface.

2.????? In-Sequence Delivery (AM mode): Ensures data arrives in the correct order even after re-establishment procedures.

3.????? Duplicate Detection (AM mode): Prevents redundant data delivery after re-establishment.

4.????? Retransmission (AM mode): Re-sends lost data packets during handovers in connected mode for reliable delivery.

5.????? Timer-Based Discard (Uplink): Removes outdated data exceeding a specific time limit in the uplink direction.

6.????? Ciphering and Deciphering: Encrypts user data for secure transmission and decrypts it upon arrival (AES is mandatory).

7.????? Integrity Protection and Verification: Adds and verifies integrity checks to safeguard data from tampering.

8.????? Transfer of Control Plane Data: Also handles the transfer of control plane data (signaling messages) for network management.

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PDCP operates independently for UP and control plane data, offering tailored security and efficiency.

Ciphering and integrity protection are mandatory for UP data, while optional for control plane data based on security needs.

PDCP interacts closely with RLC and MAC for seamless data flow and delivery.

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Service Data Adaptation Protocol (SDAP) Layer

Within the complex ecosystem of 5G, the Service Data Adaptation Protocol (SDAP) plays a crucial role in ensuring efficient and tailored data delivery. Think of it as a "traffic translator", adapting user plane data to meet the specific requirements of different services and applications.

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1.????? Traffic Translator: Matches diverse service needs (voice, video, etc.) to dedicated network channels (DRBs) for optimal flow.

2.????? Priority Manager: Embeds QoS Flow IDs (QFIs) in data packets, guiding the network on how to handle each stream based on its importance.

3.????? Flexible Adaptor: Works in both downlink and uplink, ensuring priority treatment even for data originating from your device.

4.????? Slicing Enabler: Plays a crucial role in network slicing, allowing creation of virtual networks with tailored QoS for specific needs.

5.????? Efficiency Booster: Reduces congestion and maximizes resource utilization by guiding data through the most appropriate channels.

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PHYSICAL Layer of 5G-NR |Layer 1

The 5G New Radio (NR) physical layer acts as the foundation for seamless communication, transforming data into radio signals and back again. Imagine it as the information highway infrastructure, ensuring efficient and reliable data transmission. Here's a breakdown of its key functions:

1.????? Error Detection & Correction: Acts as a vigilant inspector, identifying and correcting errors that might occur during transmission using powerful Forward Error Correction (FEC) encoding/decoding. Think of it like adding backup copies and checksums to your data for error-free delivery.

2.????? Rate Matching & Channel Mapping: Adjusts the data rate to precisely fit the capacity of available physical channels and maps it efficiently, like a skilled architect optimizing space on the highway.

3.????? Modulation & Demodulation: Transforms digital data into radio signals for transmission and back again upon reception, acting as the translator between the digital and physical worlds.

4.????? Frequency & Time Synchronization: Ensures all devices are in perfect sync, like an orchestra conductor coordinating musicians, minimizing interference and maximizing efficiency.

5.????? MIMO Antenna Processing: Utilizes multiple antennas to create stronger, more reliable signals, comparable to having multiple lanes on the highway to increase traffic flow.

6.????? Transmit Diversity: Sends the same data through multiple antennas, like building redundant routes, to ensure it reaches its destination even if one path encounters obstacles.

7.????? Beamforming: Focuses radio signals towards specific users, akin to directing headlights for clear communication and reduced interference.

8.????? Radio Characteristics Measurements: Continuously monitors channel conditions (signal strength, interference) and reports them to higher layers, like sending real-time traffic updates to optimize data flow.

Reference : 3gpp specs 38 series

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