Understanding cellular network infrastructure and components
Cellular network architecture consists of multiple interconnected subsystems working together to provide wireless communication services. The architecture has evolved significantly from 2G to 5G, becoming more flexible and software-defined.
Modern networks separate into three main domains: Radio Access Network (RAN), Core Network, and Transport Network. Each domain serves specific functions in establishing and maintaining connections.
The architecture follows a hierarchical structure, with user equipment at the edge, base stations providing radio access, and core network elements managing sessions, mobility, and interconnection with external networks.
Mobile devices with radio transceivers and protocol stacks for network access.
Radio transceivers managing air interface and radio resources.
Central infrastructure handling authentication, routing, and services.
The radio link between UE and base station uses specific frequency bands and protocols. Physical layer handles modulation, coding, and transmission. MAC layer manages resource allocation and scheduling.
Base stations perform radio resource management, mobility control, scheduling, and interference coordination. They connect to core network via backhaul links using fiber or microwave.
Networks divide coverage into cells, each served by base station sectors. Cell sizes range from macro cells (several kilometers) to small cells (tens of meters) depending on capacity needs.
Handles signaling, authentication, and tracking area management.
Routes user data packets between RAN and core network.
Connects to external packet data networks and internet.
Stores subscriber profiles, authentication, and authorization data.
Handles connection and mobility management for UE.
Manages PDU sessions and IP address allocation.
Forwards and routes user data packets.
Manages subscriber data and authentication credentials.
Air interface between UE and base station. Carries both user data and control signaling over radio frequencies.
Radio InterfaceConnects eNodeB to EPC in LTE networks. S1-MME for control plane, S1-U for user plane data.
Backhaul InterfaceDirect connection between base stations for handover coordination and interference management.
Inter-Base StationReference point between UE and AMF in 5G for NAS signaling.
5G InterfaceConnects gNB to AMF in 5G networks for control plane signaling.
5G InterfaceUser plane interface between gNB and UPF for data transmission in 5G.
5G Interface
Networks track user location and manage handovers as devices move between cells. Tracking areas group multiple cells to reduce signaling overhead.
Handover procedures transfer active connections between base stations seamlessly. Hard handovers break-before-make, while soft handovers maintain multiple connections temporarily.
Core network establishes, modifies, and releases data sessions (bearers in 4G, PDU sessions in 5G). Quality of Service parameters define bandwidth, latency, and reliability requirements.
Authentication verifies subscriber identity using SIM credentials. Encryption protects data over air interface. Integrity protection prevents tampering with signaling messages.
Connects base stations to core network. Technologies include fiber optic cables, microwave links, and millimeter-wave connections. Requires high capacity and low latency.
In C-RAN architectures, connects distributed units (DU) to centralized units (CU). Enables functional splits and centralized processing for efficiency.
Links remote radio heads to baseband processing units. Requires very high bandwidth and strict latency constraints. Common Point-to-Point Protocol Radio Interface (CPRI).
Network slicing creates multiple virtual networks on shared physical infrastructure, each optimized for specific use cases.
Enhanced Mobile Broadband
High bandwidth for video streaming, AR/VR applications. Optimized for throughput over latency.
Ultra-Reliable Low Latency
Mission-critical applications requiring guaranteed reliability and minimal latency.
Massive Machine Type Communications
Supports massive numbers of IoT devices with minimal power consumption.
