Telecommunications Networks & Signal Processing

# Telecommunications Networks & Signal Processing Knowledge Pack

## Network Architecture Fundamentals

### The OSI Model in Practice
The 7-layer OSI model remains the foundation for understanding telecom networks. In real deployments, focus on how layers interact: Physical (Layer 1) handles RF transmission and fiber optics, Data Link (Layer 2) manages MAC addressing and frame delivery, Network (Layer 3) handles IP routing. In modern telecom, the clean separation blurs — SDN collapses control planes, NFV virtualizes functions that were once physical appliances.

Practical insight: Most network troubleshooting follows a bottom-up approach. If a UE can't connect, start at Layer 1 (RF signal strength, SINR measurements), then check Layer 2 (authentication, association), then Layer 3 (IP assignment, routing). 80% of issues live in Layers 1-3.

### RAN Architecture
The RAN connects UE to the CN. In 4G LTE, the base station (eNodeB) connects directly to the Evolved Packet Core. In 5G NR, the gNB architecture splits into Central Unit (CU), Distributed Unit (DU), and Radio Unit (RU). This disaggregation enables flexible deployment: CU can be centralized in a data center, DU placed at cell sites, RU on the tower.

Open RAN initiative disaggregates further with standardized interfaces (fronthaul, midhaul, backhaul), enabling multi-vendor interoperability. Key interfaces: F1 (CU-DU), Open Fronthaul (DU-RU). Benefit: operators avoid vendor lock-in. Challenge: integration complexity and latency sensitivity on fronthaul links (requires sub-100 microsecond timing).

### Core Network Evolution
The CN handles authentication, session management, policy enforcement, and routing to external networks. 5G CN is fully cloud-native, built on microservices architecture with service-based interfaces (SBI). Key network functions: AMF (access and mobility), SMF (session management), UPF (user plane function), PCF (policy control), UDM (unified data management).

Network slicing allows operators to create multiple virtual networks on shared physical infrastructure. Each slice has tailored QoS parameters: enhanced mobile broadband (eMBB) for high BW, ultra-reliable low-latency communication (URLLC) for industrial IoT, massive machine-type communication (mMTC) for sensor networks.