Part 5: 5G NSA — Conceptual Lab Exercise

Learning Objective: Understand how a 5G NSA deployment would differ from the SA lab in Part 4, and why it cannot be replicated with UERANSIM.

Why No Hands-On NSA Lab?

The Technical Gap

What Would Be Needed for a Real NSA Lab

graph TB
    subgraph "What UERANSIM CAN do"
        gNB[✅ gNB
5G NR]
        UE_SA[✅ UE
5G SA only]
    end
    
    subgraph "What NSA REQUIRES (not supported)"
        eNB[❌ eNB
4G LTE Master]
        UE_NSA[❌ UE
Dual-mode LTE+NR]
        X2[❌ X2 Interface
eNB↔gNB coordination]
    end
    
    subgraph "Open5GS Core"
        MME[MME
4G control plane]
        AMF[AMF
5G control plane]
        SGW[SGW
4G user plane]
        UPF[UPF
5G user plane]
    end
    
    eNB -->|S1-MME| MME
    eNB -->|S1-U| SGW
    gNB -->|X2| eNB
    gNB -.->|S1-U| SGW
    UE_NSA -->|LTE| eNB
    UE_NSA -.->|NR| gNB
    
    style eNB fill:#ffcccc
    style UE_NSA fill:#ffcccc
    style X2 fill:#ffcccc
    style gNB fill:#ccffcc
    style UE_SA fill:#ccffcc

Conceptual Exercise: NSA Architecture Differences

Exercise 1: Compare Core Components

Using what you learned in Part 2 (NSA Architecture) and Part 4 (SA Lab), fill in this table:

Exercise 2: NSA Docker-Compose Design

If you could build an NSA lab (using srsRAN instead of UERANSIM), what would the docker-compose.yml look like? Design the service list:

Your answer should include:

1. Which Open5GS NFs are needed? (Hint: no 5G core NFs like AMF/NRF)
2. What RAN components?
3. How many Docker networks?
4. Which ports would the eNB use to connect to MME?

# NSA docker-compose (conceptual — requires srsRAN, not UERANSIM)
services:
  mongodb:         # Subscriber database
  webui:           # Web management
  hss:             # Home Subscriber Server (Diameter)
  pcrf:            # Policy & Charging Rules (Diameter)
  mme:             # Mobility Management Entity (S1AP, GTP-C)
  sgwc:            # Serving Gateway - Control (GTP-C, PFCP)
  sgwu:            # Serving Gateway - User (GTP-U)
  smf:             # Session Mgmt / PGW-C (GTP-C, PFCP)
  upf:             # User Plane / PGW-U (GTP-U)
  
  # NOTE: No AMF, AUSF, UDM, UDR, NRF, SCP, NSSF, BSF needed!
  
  srsran_enb:      # srsRAN eNB (LTE master node)
  # srsran_gnb:    # Optional: srsRAN gNB for EN-DC
  srsran_ue:       # srsRAN UE

# Networks:
#   cp_net: 172.22.0.0/24  (MME, HSS, PCRF, SGW-C, SMF)
#   up_net: 172.23.0.0/24  (SGW-U, UPF)
#   ran_net: 172.24.0.0/24 (eNB, gNB, UE)

# Key difference: eNB connects to MME on port 36412 (S1AP/SCTP)
# not port 38412 (NGAP) like in 5G SA

Exercise 3: Security Comparison

Answer these questions comparing NSA vs SA security:

1. IMSI Privacy: In NSA mode, is the subscriber identifier encrypted? Why or why not?
2. Inter-NF Communication: NSA uses Diameter between MME and HSS. SA uses SBI HTTP/2. Which is easier to secure with mTLS?
3. Network Slicing: Can an NSA network support network slicing? What's missing?
4. Authentication: NSA uses 4G AKA. SA uses 5G-AKA. What's the key privacy improvement in 5G-AKA?

Alternative: srsRAN for Real NSA Testing

If you want to build a genuine NSA lab in the future:

srsRAN 4G (Open-Source LTE eNB + UE)

# Clone srsRAN 4G
git clone https://github.com/srsran/srsRAN_4G.git

# Build from source (requires UHD drivers or ZMQ for simulation)
cd srsRAN_4G && mkdir build && cd build
cmake .. -DENABLE_ZMQ=ON  # ZMQ for software-only simulation
make -j$(nproc)

# Key binaries:
# srsenb  - eNB simulator
# srsue   - UE simulator  
# srsmbms - MBMS gateway

Resources

Summary

• ✅ Understood why UERANSIM cannot simulate NSA/EN-DC
• ✅ Compared NSA vs SA core architecture requirements
• ✅ Designed a conceptual NSA docker-compose
• ✅ Analyzed security differences between NSA and SA
• ✅ Identified srsRAN 4G as the correct tool for NSA testing

Next: Part 6: Docker Lab - 5G SA Deep Dive →