1141 NB-IoT Network Architecture

1141.1 Learning Objectives

By the end of this chapter, you will be able to:

Describe Network Components: Identify key elements in NB-IoT end-to-end architecture
Explain Data Flow: Trace data path from device through EPC to application server
Configure Core Components: Understand MME, S-GW, P-GW, and SCEF functions
Design IoT Connectivity: Plan device-to-cloud architecture using NB-IoT

1141.2 Prerequisites

Required Chapters:

NB-IoT Fundamentals - Core concepts
NB-IoT Deployment Modes - Deployment options
Cellular IoT Fundamentals - Cellular context

Technical Background:

Basic networking concepts
LTE/4G network understanding
IoT device communication patterns

Estimated Time: 25 minutes

1141.3 NB-IoT End-to-End Architecture

NB-IoT leverages existing LTE infrastructure with IoT-specific optimizations. The architecture spans from constrained devices through cellular network to cloud applications.

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graph TB
    subgraph "User Equipment (UE)"
        METER["Smart Meter<br/>(PSM Mode)"]
        TRACKER["Asset Tracker<br/>(eDRX Mode)"]
        PARKING["Parking Sensor<br/>(PSM Mode)"]
    end

    subgraph "Radio Access Network"
        ENB["eNodeB<br/>(Base Station)<br/>180 kHz NB-IoT carrier"]
    end

    subgraph "Evolved Packet Core (EPC)"
        MME["MME<br/>(Mobility Management)<br/>Authentication, Security"]
        SGW["S-GW<br/>(Serving Gateway)<br/>Packet Routing"]
        PGW["P-GW<br/>(PDN Gateway)<br/>Internet Access via APN"]
        SCEF["SCEF<br/>(Service Capability)<br/>IoT Optimization"]
    end

    subgraph "Application Layer"
        APP["Application Server<br/>(Customer Cloud)"]
        DASH["Dashboard<br/>(Analytics)"]
    end

    METER -.->|Uplink: < 5 µA sleep| ENB
    TRACKER -.->|Uplink: 15 µA eDRX| ENB
    PARKING -.->|Uplink: < 5 µA sleep| ENB

    ENB -->|S1 Interface| MME
    ENB -->|User Plane| SGW

    MME <--> SGW
    SGW <--> PGW
    PGW <--> SCEF

    SCEF --> APP
    PGW --> DASH

    style METER fill:#2C3E50,color:#fff
    style TRACKER fill:#2C3E50,color:#fff
    style PARKING fill:#2C3E50,color:#fff
    style ENB fill:#16A085,color:#fff
    style MME fill:#E67E22,color:#fff
    style SGW fill:#E67E22,color:#fff
    style PGW fill:#E67E22,color:#fff
    style SCEF fill:#F39C12,color:#fff
    style APP fill:#3498DB,color:#fff

Figure 1141.1: NB-IoT End-to-End Network Architecture with EPC Components

1141.4 Architecture Layers

1141.4.1 Layer 1: IoT Devices (NB-IoT UE)

Device	Function	Interface
Smart Meter	Utility monitoring	Uu Interface, 180 kHz
Asset Tracker	Location tracking	PSM/eDRX
Parking Sensor	Occupancy detection	Coverage Extension

NB-IoT User Equipment (UE) devices are characterized by:

Low complexity: Single antenna, half-duplex operation
Power optimization: PSM and eDRX support
Narrow bandwidth: 180 kHz radio
Extended coverage: Up to 164 dB MCL

1141.4.2 Layer 2: Radio Access Network

Component	Function	Capacity
eNodeB (Base Station)	Radio access	180 kHz carrier per NB-IoT cell

The eNodeB provides:

NB-IoT carrier management: 180 kHz dedicated or shared
Coverage enhancement: Repetition coding for extended range
Power class support: Different TX power levels
Scheduling: Resource allocation for uplink/downlink

1141.4.3 Layer 3: Evolved Packet Core (EPC)

The EPC is the heart of the NB-IoT network, providing:

Component	Abbreviation	Function
MME	Mobility Management Entity	Authentication, session management
S-GW	Serving Gateway	User plane routing
P-GW	PDN Gateway	Internet connectivity, APN
HSS	Home Subscriber Server	Subscriber database
SCEF	Service Capability Exposure Function	API exposure, non-IP data

1141.4.4 Layer 4: Application Layer

Component	Function	Protocol
IoT Platform	Device management	REST/MQTT
Application Server	Business logic	Application-specific

1141.5 EPC Components Deep Dive

1141.5.1 Mobility Management Entity (MME)

The MME handles control plane functions:

Authentication: Validates device identity using USIM
Security: Establishes encryption keys
Session Management: Creates/modifies/deletes bearers
Paging: Notifies devices of incoming data
TAU Handling: Tracks device location (Tracking Area Update)

For Beginners: What is the MME?

Think of the MME as a security guard and receptionist combined:

Security Guard: Checks your ID (authentication) when you enter
Receptionist: Keeps track of where you are (location tracking)
Concierge: Helps set up your connection (session management)

When your NB-IoT device first connects, the MME: 1. Asks “Who are you?” (authentication) 2. Sets up a secure connection (encryption) 3. Remembers where you are (tracking area) 4. Notifies you if someone wants to reach you (paging)

1141.5.2 Serving Gateway (S-GW)

The S-GW handles user plane routing:

Packet forwarding: Routes data between device and P-GW
Buffering: Stores packets while device is sleeping
Mobility anchor: Maintains connection during handover
Lawful intercept: Supports legal monitoring requirements

1141.5.3 PDN Gateway (P-GW)

The P-GW connects to external networks:

IP address allocation: Assigns IP to devices
APN management: Access Point Name for different services
Policy enforcement: QoS and charging rules
Internet access: Gateway to public/private networks

1141.5.4 Service Capability Exposure Function (SCEF)

The SCEF is NB-IoT-specific, optimizing IoT data delivery:

Non-IP data delivery (NIDD): Small data without IP overhead
API exposure: RESTful APIs for application servers
Device triggering: Wake sleeping devices
Group messaging: Efficient multicast

SCEF: The IoT Optimizer

The SCEF is what makes NB-IoT efficient for IoT applications:

Without SCEF (traditional path): Device → eNB → S-GW → P-GW → Internet → App Server - Requires full IP stack - Each packet has 40+ byte IP/TCP overhead - High latency for small payloads

With SCEF (optimized path): Device → eNB → MME → SCEF → App Server - Non-IP Data Delivery (NIDD) - Minimal overhead for small payloads - Direct API access for applications

1141.6 Data Flow Paths

1141.6.1 User Plane (Data) Flow

Device → eNodeB → S-GW → P-GW → Internet → Application Server

Used for IP-based data (MQTT, CoAP over UDP)
Full IP stack required on device
Supports larger payloads

1141.6.2 Control Plane (Signaling) Flow

Device → eNodeB → MME → SCEF → Application Server

Used for small data (< 1600 bytes)
Minimal overhead (Non-IP Data Delivery)
Optimized for infrequent transmissions

1141.6.3 Downlink Data Path

When application server sends data to device:

Device in connected mode: Direct delivery via S-GW
Device in idle mode: MME sends paging, device wakes, then delivery
Device in PSM: Data buffered at P-GW until TAU timer expires

1141.7 Interface Specifications

1141.7.1 Key Interfaces

Interface	Endpoints	Function
Uu	UE ↔︎ eNodeB	Air interface (radio)
S1-MME	eNodeB ↔︎ MME	Control plane signaling
S1-U	eNodeB ↔︎ S-GW	User plane data
S11	MME ↔︎ S-GW	Control for user plane
S5/S8	S-GW ↔︎ P-GW	User plane between gateways
T6a	SCEF ↔︎ MME	IoT optimization
Tsp	SCEF ↔︎ App Server	API exposure

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graph LR
    UE["IoT Device"]
    ENB["eNodeB"]
    MME["MME"]
    SGW["S-GW"]
    PGW["P-GW"]
    SCEF["SCEF"]
    APP["App Server"]

    UE -->|"Uu<br/>(Air)"| ENB
    ENB -->|"S1-MME<br/>(Control)"| MME
    ENB -->|"S1-U<br/>(User Data)"| SGW
    MME -->|"S11"| SGW
    SGW -->|"S5/S8"| PGW
    MME -->|"T6a"| SCEF
    SCEF -->|"Tsp"| APP
    PGW -->|"Internet"| APP

    style UE fill:#2C3E50,color:#fff
    style ENB fill:#16A085,color:#fff
    style MME fill:#E67E22,color:#fff
    style SGW fill:#E67E22,color:#fff
    style PGW fill:#E67E22,color:#fff
    style SCEF fill:#F39C12,color:#fff
    style APP fill:#3498DB,color:#fff

Figure 1141.2: NB-IoT Network Interfaces

1141.8 CIoT Optimizations

NB-IoT includes Cellular IoT (CIoT) specific optimizations:

1141.8.1 Control Plane CIoT EPS Optimization

Small data sent via signaling (no user plane setup)
Reduced latency for infrequent transmissions
Lower power consumption

1141.8.2 User Plane CIoT EPS Optimization

Suspended user plane (fast resume)
Connection release assistance
Optimized for periodic reporting

1141.8.3 Data over NAS (DoNAS)

Data piggybacked on NAS signaling
No dedicated bearer required
Ideal for <1600 byte payloads

1141.9 Knowledge Check

Question: Match each NB-IoT feature to its primary cellular IoT advantage:

NB-IoT Features: 1. Licensed spectrum operation 2. 164 dB Maximum Coupling Loss 3. PSM and eDRX modes 4. Reuse of LTE eNodeB infrastructure

Cellular IoT Advantages: - A) Extreme coverage (basements, underground, rural) - B) Low deployment cost and rapid rollout - C) Carrier-grade reliability and QoS guarantees - D) 10-15 year battery life for IoT devices

Licensed spectrum (1→C): Operating in licensed cellular bands provides carrier-grade reliability, no interference from unlicensed devices, guaranteed QoS, and regulatory compliance.
164 dB MCL (2→A): +20 dB coupling loss budget vs GPRS enables deep indoor penetration (basements, underground parking, utility rooms) and extended rural coverage.
PSM/eDRX (3→D): Power-saving modes reduce sleep current from 15 mA (idle) to 5 µA (PSM) or 15 µA (eDRX), enabling 10-15 year battery life with 5 Ah battery.
LTE infrastructure reuse (4→B): In-band deployment uses existing LTE eNodeBs with software upgrade only. No new towers needed. Rapid market entry (3-6 months) vs greenfield LoRaWAN deployment (12-18 months).

1141.10 Summary

Four-layer architecture spans devices, radio access, evolved packet core, and applications
EPC components (MME, S-GW, P-GW, SCEF) provide authentication, routing, and IoT optimization
SCEF enables Non-IP Data Delivery for efficient small payload transmission without IP overhead
Two data paths exist: user plane (IP-based, larger payloads) and control plane (optimized, small data)
CIoT optimizations reduce power consumption and latency for IoT traffic patterns
Standard interfaces (S1, S5/S8, T6a) enable interoperability between network components

1141.11 What’s Next

Continue with technology comparison and selection guidance:

Next Chapter: NB-IoT Technology Comparison - NB-IoT vs LTE-M selection
Then: NB-IoT Knowledge Check - Comprehensive assessment
Related: NB-IoT Power and Channel - Power saving modes
Return to: NB-IoT Comprehensive Review - Overview and navigation