Curriculum — Level 1–5 Learning Roadmap¶
Why a systematic curriculum is needed (Why → What → How)¶
Why — The 5GC is a system in which many Network Functions (NF), such as AMF/SMF/UPF, work together on top of the SBA (Service-Based Architecture). Even if you memorize individual terms one by one, getting the order in which you learn them wrong keeps the big picture from coming together, and you will get lost even when reading the specifications.
What — This curriculum is a five-stage roadmap that starts from an overview of the 5GC (Level 1), then proceeds through basic procedures (Level 2) → mobility (Level 3) → services (Level 4) → advanced/latest topics (Level 5), arranged in the order in which prerequisite knowledge builds up.
How — First, check where you currently stand using the big picture below, then look at each Level's "learning objectives, main topics, and prerequisite Level" to decide the order in which to proceed. Beginners should start from Level 1; experienced learners can enter from whichever Level they need.
The big picture (Level 1 → Level 5)¶
flowchart TD
L1["Level 1
5GC Overview / SBA / NF"] --> L2["Level 2
Registration / Auth / PDU Session / QoS"]
L2 --> L3["Level 3
Mobility / Handover / Paging / Interworking"]
L3 --> L4["Level 4
VoNR / SMS / Emergency / Slice / RedCap"]
L4 --> L5["Level 5
Charging / Policy / NWDAF / Roaming / Rel17-18"]
L1 -.- L1t["Mobile Network / LTE / Interface"]
L2 -.- L2t["Security / Session establishment"]
L3 -.- L3t["Idle / Connected / N26"]
L4 -.- L4t["Network Slice / Voice"]
L5 -.- L5t["CAPIF / NEF / Analytics"]
Details of each Level¶
Level 1 — Mobile Network Overview / 5GC Overview¶
| Item | Content |
|---|---|
| Learning objectives | Understand the overall picture of mobile networks and the architecture (SBA) that forms the foundation of the 5GC |
| Prerequisite Level | None (this is the starting point) |
Main topics
- Mobile Network Overview (up to LTE/EPC)
- 5GC Overview and SBA (Service-Based Architecture)
- Network Function (NF) Overview
- Interface / Protocol Overview
How to work through this Level
We recommend starting from the map of 4G/LTE (Mobile Network Overview), grasping the design philosophy of the 5GC in 5GC Overview and SBA, and then getting a bird's-eye view of the building blocks in the NF Overview and Interface / Protocol Overview. You can dig deeper into individual NFs and reference points on their detail pages and in the dictionary.
Note on Interface / Protocol
N1/N2 are the control plane; N3 (gNB–UPF) / N6 (UPF–DN) are the user plane; and N4 is between the SMF and UPF (PFCP). Separately, there is the SBI (Service-Based Interface — the service-based interfaces such as Namf/Nsmf/Nudm), over which NFs interoperate using HTTP/2 (TS 23.501 §4). User-plane packets are encapsulated with GTP-U and carried over N3.
When you want to look up a term first
You can look ahead at the names of NFs, Interfaces, and Protocols in the Dictionary.
Level 2 — Basic Procedures (Registration / Session)¶
| Item | Content |
|---|---|
| Learning objectives | Be able to follow, via the Call Flow, the basic procedure by which a UE registers to the network and establishes a communication path (PDU Session) |
| Prerequisite Level | Level 1 |
Main topics
- Registration (initial registration)
- Authentication
- Security
- PDU Session (PDU Session establishment)
- PDU Session Modification / Release
How to work through this Level
First, follow the process up to the UE registering to the network in Registration (initial registration), and then proceed to Authentication, Security, and PDU Session; this connects the whole flow up to the point where the communication path is opened. Each chapter has Call Flow diagrams, real Wireshark examples, and comprehension checks. QoS (the 5G QoS model) is placed in Level 3.
The relationship between Authentication and Security
Authentication (5G-AKA / EAP-AKA') and NAS/AS Security (key hierarchy, encryption, integrity protection) are separate topics, but in practice they occur as a continuous sequence right after Registration. The subscriber identifier is not sent as the SUPI directly; it is sent as the SUCI, concealed with a public key (TS 33.501).
Experienced learners start here
If you want to learn by doing, start with Registration (initial registration). It is a central procedure in the 5GC and forms the foundation for many other chapters.
Level 3 — Mobility / QoS¶
| Item | Content |
|---|---|
| Learning objectives | Understand the mechanisms that keep communication uninterrupted even as the UE moves (Mobility/Handover), as well as the 5G QoS model and network slicing |
| Prerequisite Level | Level 2 |
Main topics
- Handover
- Paging
- Service Request
- RRC Resume / Small Data (lightweight resumption)
- Mobility Registration Update
- Periodic Registration Update
- QoS (5G QoS model)
- Network Slicing
- 4G-5G Interworking (N26 / interworking with the 4G EPC)
- EPS Fallback (the mechanism that switches from 5G to 4G to make voice work)
How to work through this Level
First, grasp the "stays connected while moving, can be paged" mechanisms in Handover and Paging, then expand to Service Request / RRC Resume and the registration-update topics (Mobility / Periodic). For QoS and slices, cover QoS / Network Slicing. If you are interested in 4G/5G interworking, N26 Interface, Interworking, and EPS Fallback are the core.
What is EPS Fallback
In early 5G deployments, there are many areas where VoNR is not yet available, so EPS Fallback, which temporarily drops the UE to 4G (EPS) to make voice work on incoming/outgoing calls, is virtually mandatory in real-world operation (TS 23.502 §4.13.6.1).
Level 4 — Services / Device Categories (Voice / Slice / RedCap, etc.)¶
| Item | Content |
|---|---|
| Learning objectives | Understand the main services such as voice, emergency calls, and network slices, as well as device categories such as RedCap |
| Prerequisite Level | Level 2. In addition, for voice (VoNR/Emergency), understanding Level 3 (mobility) is also recommended |
Main topics
- VoNR (Voice over NR)
- EPS Fallback (switching from 5G to 4G to make voice work)
- SMS (Short Message Service)
- Emergency (emergency calls)
- RedCap (Reduced Capability, Rel-17)
How to work through this Level
The voice-related topics (VoNR / EPS Fallback / Emergency) are closely related, so reading them together helps understanding. SMS, which is carried over the control plane, and RedCap, a device category, can be read independently. For network slices, refer to Network Slicing in Level 3.
VoNR / Emergency assume IMS
VoNR and Emergency (voice) assume the IMS (IP Multimedia Subsystem), and voice is tied to QoS Flow (5QI=1: conversational voice; 5QI=5: IMS signaling. TS 23.501 §5.7.4, the table of standardized 5QIs). In areas where VoNR cannot be used, voice is made to work via EPS Fallback in Level 3.
RedCap is not a service but a device category
RedCap is not a service provided by the 5GC like SMS/VoNR; it is a device category with reduced UE capability (Reduced Capability, Rel-17). It refers to a device type in which UE capabilities such as bandwidth and the number of antennas are intentionally scaled down, aimed at low-cost, low-power mid-tier IoT.
Level 5 — Advanced / Latest Releases¶
| Item | Content |
|---|---|
| Learning objectives | Get a bird's-eye view of advanced areas such as charging, policy, data analytics, and roaming, as well as the latest features of Rel-17/18 |
| Prerequisite Level | Level 1–4 (varies by topic) |
Main topics
- Charging
- Policy (policy control / PCF)
- NWDAF (data analytics / Analytics)
- Roaming (roaming / SEPP・N32)
- NEF・CAPIF (network capability exposure)
- Advanced Security (advanced 5GC security)
- Rel-17 & Rel-18 (5G-Advanced)
- Location Service (LCS / GMLC・LMF)
How to work through this Level
The advanced areas are highly independent, so you can read them starting from whichever topic interests you. For charging and policy, Charging / Policy; for data analytics, NWDAF; for inter-operator interworking, Roaming; for external exposure, NEF・CAPIF; for the latest features, Rel-17 & Rel-18; and for positioning, Location Service are the entry points.
The relationship between Analytics and NWDAF
Analytics (data analytics) and NWDAF may look like separate items, but the NWDAF (Network Data Analytics Function) is the very NF that handles Analytics, and it exposes the service-based interface Nnwdaf that provides analytics results to other NFs (TS 23.288). For details, refer to the NWDAF chapter.
Start learning and looking things up¶
From each Level's "Main topics", go directly to whichever chapter interests you. If this is your first time, proceed in order from Level 1; if you have 4G/LTE experience, we recommend getting hands-on from Registration (initial registration) in Level 2.
When you want to look up a term quickly, use the Dictionary; for details on NFs and Interfaces, using individual NF pages such as AMF and individual Interface pages such as N2 together will deepen your understanding.