Cellular Network Architecture: A Beginner’s Guide to 2G, 3G, 4G and 5G

Cellular network architecture is the fundamental framework enabling smartphones, IoT devices, and connected vehicles to communicate seamlessly. This guide serves as an introduction for software engineers, IoT builders, and operations personnel. You will gain insights into the Radio Access Network (RAN), transport systems, core networks, service layers, and how they all interact across 2G, 3G, 4G, and 5G technologies. We will share practical advice, terminology, and resources designed to enhance your understanding and application of these systems.

How to Use This Guide

• Developers: Focus on the “Fundamentals”, “Performance & Quality”, and practical checklist sections.
• Network Engineers: Review “Core Components”, “Generational Differences”, and “Trends”.
• Product Managers: Skim through use cases and deployment types to match connectivity to business needs.

A glossary at the end will clarify terms as you learn.

Cellular Fundamentals — Key Concepts

What is a “Cell”?

A cell refers to a geographic area served by a single radio transceiver, essentially creating a coverage bubble. The base station within this area manages radio traffic for devices located inside it.

Cell Sizes:

• Macro Cell: Covers large areas (kilometers); used for broad outdoor coverage.
• Micro Cell: Provides service for smaller areas (hundreds of meters); ideal for urban streets and hotspots.
• Pico Cell: Designed for indoor coverage (tens of meters); typically found in malls and stations.
• Femto Cell: A small base station for home or office use, serving individual households.

Cells utilize frequency reuse to scale capacity across regions, fundamentally enhancing user accessibility.

Base Stations: BTS, NodeB, eNodeB, gNodeB

Each generation of cellular technology has distinct nomenclature for base stations, yet their functions remain consistent: transmitting and receiving radio signals, scheduling resources, and managing connections.

• 2G: BTS (Base Transceiver Station)
• 3G: NodeB
• 4G: eNodeB (Evolved NodeB)
• 5G: gNodeB

Functionality includes modulating and demodulating signals, coordinating handovers, and radio scheduling — similar to how a post office manages mail delivery timelines.

Handover and Mobility Management

Handover ensures a user’s active session continues as they move between cells. Types of handovers include:

• Intra-Cell: Changes within the same cell.
• Inter-Cell (Same RAT): Movement between cells using the same radio technology (e.g., LTE to LTE).
• Inter-RAT: Transitioning between different generations (e.g., 4G to 3G).

Robust handover protocols minimize latency during transitions and help maintain a steady user experience.

Spectrum and Channels (Basics)

Spectrum comprises radio frequency bands, each with its advantages and disadvantages:

• Lower Frequencies (e.g., 700 MHz): offer extensive coverage and better penetration through buildings.
• Higher Frequencies (e.g., 3.5 GHz, mmWave): provide more bandwidth but lower range, excellent for capacity.

Licensed spectrum is reserved for cellular use by operators, whereas unlicensed frequencies (e.g., Wi-Fi) are shared among devices.

Carrier aggregation in LTE and 5G combines multiple bands to enhance bandwidth efficiency.

Core Components of Cellular Architecture

Radio Access Network (RAN)

RAN encompasses all radio functions, including:

• Physical RF and Antennas
• Medium Access Control and Scheduling
• Baseband Processing

RAN can be centralized or distributed:

• Distributed RAN: Traditional model with co-located baseband and radio.
• C-RAN (Centralized RAN): Centralizes baseband processing in data centers, reducing costs and improving coordination.
• vRAN: Virtualized RAN functions on common server infrastructures, enabling flexibility.

Densifying network capacity using small cells helps manage areas with high user concentrations.

Transport Network

The transport network connects the RAN to the core and is divided into three segments:

• Fronthaul: Connects remote radio heads to baseband units, requiring low latency.
• Midhaul: Links pooled baseband units to upper layers of the network.
• Backhaul: Directs traffic between the RAN and core network.

Transport mediums typically include fiber (ideal), microwave, and Ethernet, with quality metrics directly affecting user experience especially in latency-sensitive applications.

Check out our SD-WAN implementation guide for insights into transport design strategies.

Core Network (EPC and 5G Core)

The evolution from circuit-switched PSTN/SS7 to packet-based systems led to cloud-native core designs. Notable milestones in this progression include:

• 4G: Evolved Packet Core (EPC) supporting all-IP architecture.
• 5G: 5G Core (5GC) with service-based architecture.

Refer to 3GPP for authoritative specifications.

Key differences:

• 4G EPC: Monolithic structure with limited flexibility.
• 5G Core: Microservices and containerization, enabling network slicing and edge deployments.

OSS/BSS and Service Layers

• OSS (Operations Support Systems): Oversee network monitoring, configuration, and fault management.
• BSS (Business Support Systems): Manage billing, subscriptions, and settlements with partners.
• IMS (IP Multimedia Subsystem): Facilitates voice and real-time sessions like VoLTE.

APIs for additional value-added services like SMS and location operate above the core and OSS/BSS layers.

Generational Differences: 2G → 3G → 4G → 5G

Understanding these transitions is essential as networks shift from hardware to virtualized, cloud-native architectures, allowing for quicker deployments and better scalability. For insights on 5G features, refer to Ericsson’s Technology Review.

Performance & Quality: What Affects Speed, Latency, and Reliability

Throughput vs. Latency vs. Capacity

• Throughput (Mbps): Measures data per second.
• Latency (ms): Time taken for a packet to travel end-to-end.
• Capacity: Number of users/sessions the network can accommodate simultaneously.

Improving throughput often demands greater spectrum or denser cells, while minimizing latency typically requires faster transport and efficient core processing.

Coverage, Cell Load, and Interference

High user density and interference can reduce throughput per user. Strategies to mitigate these issues include:

• Utilizing MIMO (multiple antennas) and beamforming technology.
• Implementing small cells to enhance capacity in busy areas.
• Balancing load across cells and frequency bands.

Real-World Measurement Tips

Essential tools for testing network performance:

• ping: Measures latency.
• traceroute/tracert: Displays the packet path.
• iperf3: Tests throughput to a designated server.
• curl: Evaluates HTTP endpoints and download times.
• speedtest CLI: Assesses broadband-like speeds.

Example iperf3 command usage:

# Run server (remote/cloud)
ipc -s

# Run client from device
iperf3 -c <server-ip> -t 10 -P 4

For deeper diagnostics, Wireshark can analyze LTE/5G protocols (look for S1AP, NGAP).

Monitoring Performance Metrics

Developers should monitor several key metrics:

• Latency
• Jitter
• Packet loss
• Time-to-first-byte
• Handover performance in poor signal conditions

Security and Privacy Basics

Authentication and Subscriber Identity

The SIM / USIM card stores credentials that facilitate mutual authentication between devices and the network. The IMSI (International Mobile Subscriber Identity) identifies each subscriber, while temporary IDs limit exposure.

Common Threats and Mitigations

Threats include:

• Eavesdropping and interception, mitigated by air-interface encryption.
• IMSI catchers (fake base stations) that trick devices into revealing IMSIs.
• Signaling attacks that can overload control messages.
• Roaming fraud and billing attacks.

Effective defenses include mutual authentication, robust encryption, vigilant monitoring, and minimizing open interfaces.

Security in Modern Architectures (5G)

5G enhances authentication and offers service-based interfaces. However, open interfaces and virtualization introduce new vulnerabilities, necessitating:

• Secure practices for containers and VMs (e.g., regular patching).
• Network isolation for tenant slices.
• Strong API authentication within service functions.

For further guidance on 5G strategy and security, consult the GSMA’s resources.

Deployment Types and Use Cases

Public vs. Private Cellular Networks

• Public Networks: Serve consumers using carrier infrastructure and spectrum.
• Private Networks: Deployed by enterprises for specialized coverage and improved control, a trend gaining popularity in industrial IoT.

To experiment with private networks at home, check our guide on building a home lab.

Industry Use Cases

• eMBB (Enhanced Mobile Broadband): Focused on high-quality consumer video and media.
• mMTC (Massive Machine-Type Communications): Targets massive IoT implementations using NB-IoT/LTE-M.
• URLLC (Ultra-Reliable Low-Latency Communications): Relevant for applications needing fast responses, such as remote control.

Notable examples include smart factories employing private 5G in conjunction with edge computing for optimized control.

Edge Computing & MEC

Multi-Access Edge Computing (MEC) locates computing resources near the RAN to minimize latency and offer localized services (e.g., AR/VR). Edge nodes can manage UPF or application logic to cater to low-latency demands.

For IoT developers, consider edge requirements alongside device design; our guide on edge computing with ROS2/IOT will be beneficial. Read more here.

Trends and the Future (Brief)

Network Slicing and Customization

Network slicing enables operators to create specialized virtual networks tailored to different service level agreements (SLAs), enhancing pricing and service differentiation.

Open RAN and Virtualization

Open RAN (O-RAN) enhances flexibility through hardware and software disaggregation, allowing multi-vendor deployments. While fostering innovation and cost control, it introduces integration challenges.

Cloud-native functions and containerization facilitate automation and scalability akin to web services. For operators moving to this approach, check our container networking basics guide.

Integration with Other Networks

Heterogeneous networks combine resources such as Wi-Fi offload, private LTE/5G, and even satellite connections to ensure resilience and seamless device connectivity based on cost and availability.

Practical Advice for Beginners

Learning Path and Resources

Follow this suggested path:

1. Study fundamentals using this guide.
2. Review RAN and core concepts via 3GPP summaries.
3. Engage in hands-on labs, experimenting with OpenAirInterface or srsRAN.
4. Learn about transport and network automation through our guides.

Recommended tools: OpenAirInterface, srsRAN, Wireshark, iperf3.

Common Pitfalls to Avoid

• Over-optimizing for peak throughput without considering latency and coverage implications.
• Assuming all “5G” deployments yield mmWave speeds; many utilize mid or low bands for better coverage.
• Neglecting power consumption issues for IoT devices in high-throughput modes.

Checklist for Architects and Developers

Key considerations when designing applications/devices:

• Required bands and RATs for device support?
• What fallback strategies (e.g., 5G→4G→3G) will be implemented?
• How to manage roaming effectively?
• Power modes: what impact does network selection have on battery life?
• Security protocols: what are the requirements for SIM provisioning and encryption?

Testing Checklist:

• Connectivity performance under weak signal conditions.
• Handover efficiency between cells.
• Application stability during network transitions.
• Battery consumption across different RATs and frequency bands.

Example device capability JSON (for product specifications):

{
  "bands": ["n78","n41","b3"],
  "supportedRATs": ["5G", "LTE", "NB-IoT"],
  "fallback": "automatic 5G→4G→3G",
  "simProvisioning": "eSIM support",
  "powerModes": ["idle","connected","low-power"]
}

Glossary and Quick Reference

Essential terms:

• RAN: Radio Access Network — radios and base stations.
• EPC: Evolved Packet Core — 4G core.
• gNodeB: 5G base station.
• IMSI: International Mobile Subscriber Identity.
• MME: Mobility Management Entity (4G control-plane).
• UPF: User Plane Function (5G).
• MEC: Multi-access Edge Computing — edge servers adjacent to RAN.
• Network Slicing: Virtual networks featuring distinct SLAs.
• MIMO: Multiple-Input Multiple-Output (multiple antennas).
• Beamforming: Targeting radio energy toward a specific user for better efficiency.

Additional tools for hands-on practice:

• OpenAirInterface (OAI)
• srsRAN (formerly srsLTE)
• Wireshark with LTE/5G dissectors
• iperf3, ping, traceroute, speedtest

Conclusion

Cellular network architecture encompasses RAN, transport, and core layers, each of which affects coverage, performance, and security dynamics. The transition to cloud-native 5G and Open RAN introduces advanced capabilities while presenting new operational and security challenges.

As next steps, engage in a hands-on lab (srsRAN or OpenAirInterface), execute simple tests (ping, iperf3), and consult this guide’s checklist for device or application design. For more detailed guidance on home lab setup, refer to the building a home lab resource summarized earlier.

References and Further Reading

• 3GPP – The 3rd Generation Partnership Project
• GSMA – Mobile Architecture and 5G Resources
• Ericsson — What is 5G (Technology Review)

Related Guides:

• Container Networking Basics
• SD-WAN Implementation Guide
• Building a Home Lab Hardware Requirements
• Edge Computing and ROS2/IOT topics
• Network Automation with PowerShell