Inside 5G: A Breakdown of the 5G Protocol Stack

Introduction

The evolution of mobile communication has reached new heights with the introduction of 5G (Fifth Generation) technology. It promises ultra-low latency, massive connectivity, and gigabit-level speeds, fundamentally transforming industries and user experiences. One of the critical enablers of this transformation is the 5G protocol stack, which defines how data is transmitted, processed, and received across different network layers.

This article provides a deep dive into the 5G protocol stack, exploring its architecture, differences from 4G LTE, and how 5G NR (New Radio) improves efficiency, speed, and latency.

What is a Protocol Stack in 5G?

A protocol stack in 5G defines the set of communication protocols that govern data transmission between devices (UE – User Equipment), the radio access network (RAN), and the 5G Core (5GC). These protocols work together to ensure seamless, reliable, and efficient communication.

 The 5G protocol stack is divided into two main functional planes:

·       User Plane (handles actual data transfer)

·       Control Plane (manages signalling, session control, and mobility management)

Why is Control-User Plane Separation Required in 5G?

In the 5G protocol architecture, the User Plane (U-Plane) and Control Plane (C-Plane) are separated to provide more flexible, scalable, and efficient network operations. This Control and User Plane Separation (CUPS) concept was first introduced in 4G LTE (Release 14) but is a fundamental aspect of 5G architecture.

1. Scalability and Independent Scaling of Network Functions

·       In traditional LTE networks, the Control Plane (signaling functions) and User Plane (data transfer functions) were closely coupled, making network scaling rigid.

·       5G decouples these planes, allowing independent scaling of control and user plane functions based on traffic demand.

o   Example: A network experiencing high user mobility may require more Control Plane resources (AMF, SMF) but not necessarily more User Plane capacity (UPF).

2. Efficient Edge Computing and Multi-Access Edge Computing (MEC)

·       With CUPS, the User Plane functions (UPF) can be deployed closer to the user (at the edge of the network), reducing latency.

·       The Control Plane functions (AMF, SMF, etc.) remain centralized, allowing for intelligent routing and policy enforcement.

·       Use case: Autonomous Vehicles require low-latency edge computing to process critical sensor data in real-time, which is enabled by User Plane functions deployed at the edge.

3. Network Slicing and Service Differentiation

·       Network slicing allows operators to create multiple logical networks on the same physical infrastructure, each optimized for different services.

·       With CUPS, different slices can have dedicated User Plane resources while sharing Control Plane functions, enabling:

o   eMBB (Enhanced Mobile Broadband) slice: High throughput, low-latency data streaming.

o   URLLC (Ultra-Reliable Low Latency Communications) slice: Dedicated low-latency paths for real-time applications.

o   mMTC (Massive Machine-Type Communication) slice: Optimized for massive IoT devices.

4. Improved Security and Traffic Isolation

·       Separating the C-Plane and U-Plane enhances network security:

o   Control functions (authentication, mobility management) are handled centrally in a secure, hardened environment.

o   User Plane traffic can be distributed efficiently across the network without exposing control logic to potential threats.

·       Use case: A financial institution can have a separate User Plane for sensitive transactions while keeping its Control Plane secured in a private cloud.

5. Faster and More Efficient Handover Mechanisms

·       In 4G LTE, handovers involve coordination between control and user planes, leading to delays.

·       5G’s CUPS enables seamless handovers by allowing User Plane functions to remain active while Control Plane functions manage mobility, reducing service interruptions.

o   Example: A 5G-enabled high-speed train can maintain connectivity across different base stations without packet loss or session drops.

6. Enables Cloud-Native and Software-Defined Networking (SDN)

·       5G Core is designed with a Service-Based Architecture (SBA), leveraging CUPS for flexibility.

·       The Control Plane is cloud-native, allowing dynamic scaling, automation, and orchestration.

·       The User Plane can be virtualized and deployed across multiple locations, enabling Software-Defined Networking (SDN) principles. 

1. Physical Layer (PHY) – Handles Modulation, Coding, and MIMO Processing

The Physical Layer is responsible for transmitting and receiving raw data bits over the air interface between UE and the gNB (5G base station).

Key Functions in 5G:

·       Adaptive Modulation and Coding (AMC): Adjusts modulation schemes (QPSK, 16QAM, 64QAM, 256QAM) based on channel conditions.

·       Massive MIMO (Multiple Input Multiple Output): Uses hundreds of antennas to improve spectral efficiency.

·       Beamforming: Directs signals toward specific devices, reducing interference and improving coverage.

How It Differs from 4G LTE:

·       5G supports wider bandwidths (up to 400 MHz), while LTE is limited to 20 MHz per carrier.

·       Flexible numerology in 5G (subcarrier spacing from 15 kHz to 240 kHz), whereas LTE has fixed 15 kHz spacing.

·       5G NR supports both Time Division Duplex (TDD) and Frequency Division Duplex (FDD) more flexibly, while LTE mainly used FDD.

2. Medium Access Control (MAC) Layer – Controls Scheduling and Error Correction

The MAC Layer manages radio resource allocation and error correction to optimize performance.

Key Functions in 5G:

·       Dynamic Scheduling: Allocates radio resources based on network congestion and user priority.

·       Hybrid Automatic Repeat Request (HARQ): Combines error detection and retransmission for improved reliability.

·       Dynamic TDD (Time Division Duplexing): Adjusts uplink and downlink dynamically based on traffic demand.

How It Differs from 4G LTE:

·       5G NR supports slot-based scheduling, allowing for shorter transmission intervals (as low as 125µs), whereas LTE has fixed 1ms subframes.

·       5G’s HARQ operates with lower latency, enabling ultra-reliable low-latency communication (URLLC).

3. Radio Link Control (RLC) Layer – Segments and Reassembles Data Packets

The RLC Layer ensures data packets are properly segmented, reassembled, and retransmitted when needed.

Key Functions in 5G:

·       Segmentation & Reassembly: Splits large packets into smaller chunks before transmission.

Three Operating Modes:

·       Transparent Mode (TM): No retransmission, used for broadcast messages.

·       Unacknowledged Mode (UM): No retransmission but ensures error-free delivery.

·       Acknowledged Mode (AM): Ensures error-free delivery with retransmission.

How It Differs from 4G LTE:

5G supports higher data rates and optimized segmentation, making it more efficient for massive data transfer compared to LTE.

Lower retransmission delays, improving overall network responsiveness.

4. Packet Data Convergence Protocol (PDCP) Layer – Ensures Data Integrity and Security

The PDCP Layer is responsible for encryption, header compression, and reordering of packets.

Key Functions in 5G:

·       Ciphering and Integrity Protection: Encrypts and protects data transmission.

·       Header Compression (ROHC – Robust Header Compression): Reduces overhead in IP-based applications.

·       Packet Duplication for URLLC: Ensures reliability in ultra-low latency applications.

How It Differs from 4G LTE:

·       5G introduces packet duplication and reordering, enhancing reliability for mission-critical services.

·       Supports multiple DRBs (Data Radio Bearers), allowing dynamic resource allocation.

5. Service Data Adaptation Protocol (SDAP) – QoS Handling for 5G

SDAP is a new protocol introduced in 5G, missing from 4G LTE. It ensures Quality of Service (QoS) mapping between the 5G Core and the Radio Access Network (RAN).

Key Functions in 5G:

·       Maps QoS flows to Data Radio Bearers (DRBs).

·       Ensures differentiated QoS handling for services like URLLC, eMBB, and mMTC.

How It Differs from 4G LTE:

·       LTE did not have a dedicated SDAP layer, making QoS handling less flexible.

·       5G allows finer QoS control at the flow level, supporting network slicing.

6. Radio Resource Control (RRC) Layer – Manages Radio Connections and Mobility

The RRC Layer is responsible for establishing, maintaining, and releasing radio connections between the UE and the network.

Key Functions in 5G:

·       Idle Mode and Connected Mode Mobility Management.

·       Handles handovers, cell reselection, and paging.

How It Differs from 4G LTE:

·       5G RRC supports faster state transitions (e.g., Inactive → Connected) for power efficiency.

·       Dual Connectivity in 5G (NSA mode) allows UE to connect to 4G and 5G simultaneously.

7. Non-Access Stratum (NAS) Layer – Handles Session and Mobility Management

The NAS Layer ensures session management, authentication, and mobility across different network slices.

• Key Functions in 5G:

  • ·       Authentication & Security Key Management.

  • ·       Handles UE registration and de-registration.

• How It Differs from 4G LTE:

  • ·       5G NAS supports network slicing, allowing multiple virtual networks per user.

  • ·       Enhanced mobility management for seamless handovers across heterogeneous networks.

    
    

Why is the 5G Protocol Architecture Different from 4G LTE?

While 4G LTE brought significant advancements over 3G, 5G architecture introduces fundamental changes to meet the needs of emerging applications such as autonomous vehicles, IoT (Internet of Things), and Industry 4.0.

The key differences include:

1. Service-Based Architecture (SBA) in 5G Core

·       4G uses a monolithic Evolved Packet Core (EPC), while 5G implements a cloud-native, microservices-driven 5G Core (5GC).

·       5G Core network functions (e.g., AMF, SMF, UPF) communicate using HTTP/2-based APIs, improving scalability and flexibility.

2. Separation of Control and User Plane (CUPS)

·       In 4G LTE, control and user plane functions were tightly integrated.

·       5G separates these functions, allowing independent scaling and efficient edge computing.

3. Network Slicing for Customized Services

·       5G introduces network slicing, enabling the creation of multiple virtual networks tailored for different use cases (e.g., URLLC for autonomous driving, eMBB for high-speed broadband).

4. Enhanced Radio Access (5G NR vs. LTE)

·       5G uses OFDM (Orthogonal Frequency Division Multiplexing) with flexible numerology, supporting subcarrier spacing from 15 kHz to 240 kHz, compared to fixed 15 kHz in LTE.

·       Massive MIMO and beamforming improve spectrum efficiency, delivering better coverage and throughput.

How Does 5G NR (New Radio) Improve Efficiency, Speed, and Latency?

5G NR (New Radio) is the global standard for 5G wireless technology, defined by 3GPP (3rd Generation Partnership Project). It significantly enhances network performance compared to LTE.

1. Higher Data Speeds and Capacity

·       mmWave Spectrum (24 GHz - 100 GHz): Enables multi-gigabit speeds (>10 Gbps) by using wider bandwidths.

·       Dynamic Spectrum Sharing (DSS): Allows 5G to coexist with LTE in lower frequency bands.

2. Lower Latency

·       URLLC (Ultra-Reliable Low Latency Communication) enables sub-1 ms latency for mission-critical applications.

·       Flexible TTI (Transmission Time Interval): Reduces scheduling delays, improving responsiveness for real-time services.

3. Better Spectral Efficiency

·       Massive MIMO (Multiple-Input Multiple-Output): Uses hundreds of antennas to improve data throughput.

·       Beamforming: Focuses signals toward devices instead of broadcasting in all directions, enhancing efficiency.

4. Power Efficiency and Coverage Improvements

·       Dynamic TDD (Time Division Duplex): Allows flexible uplink/downlink scheduling.

·       Energy-Efficient Scheduling Algorithms: Reduce battery consumption in IoT and mobile devices.

Conclusion

The 5G protocol stack represents a significant leap in mobile communications, enabling ultra-fast speeds, low latency, and massive device connectivity. Unlike 4G LTE, 5G’s service-based architecture, network slicing, and advanced radio access techniques (5G NR) make it suitable for future technologies like autonomous vehicles, smart cities, and remote healthcare.

 References:

5G protocol stack, https://kktechkaizen.blogspot.com/2019/05/5g-protocol-stack.html

4G Vs 5G Network Architecture, https://mungfali.com/explore/4G-vs-5G-Network-Architecture