What is covered in the 5G reference section?
The 5G reference section covers architecture, interfaces, protocols, call flows, messages, troubleshooting, tools, and release-level features for 5G NR and 5G Core networks.
5G Reference: Architecture, Protocols, Call Flows & Messages
5G is the 3GPP-defined mobile system for 5G NR and 5G Core networks. This page organizes 5G architecture, interfaces, protocols, call flows, messages, troubleshooting, tools, and releases in one structured reference for engineers, testers, and learners.
5G Architecture
Understand the 5G network structure, including NG-RAN, 5GC, SBA, core functions, and radio access architecture.
5G Architecture Overview UE, NG-RAN, 5GC, SBA, and the main system map. 5G RAN / NG-RAN Architecture gNB, CU-DU split, radio bearers, and mobility. gNB in 5G Node-level view of the main 5G base station function. 5G Core Network AMF, SMF, UPF, policy, subscriber, and SBA functions. 5G SBA Service registration, discovery, and cloud-native 5GC communication. AMF in 5G Access, mobility, NAS, N1, N2, and reachability. SMF in 5G PDU sessions, N4, PFCP, UPF control, and QoS. UPF in 5G N3, N6, forwarding, QoS enforcement, and user-plane steering. VoNR Architecture Native 5G voice architecture across NR, 5GC, IMS, and QoS.
5G Interfaces
Explore the main 5G interfaces across the UE, NG-RAN, 5GC, split RAN, and service-based architecture.
N1 Interface UE to AMF NAS signalling. N2 Interface gNB to AMF NGAP control-plane signalling. N3 Interface gNB to UPF user-plane traffic. N4 Interface SMF to UPF PFCP session control. N6 Interface UPF to data network connectivity. N9 Interface UPF to UPF user-plane chaining. NG Interface NG-RAN to 5GC interface family. Xn Interface Inter-gNB mobility and coordination. F1 Interface gNB-CU to gNB-DU split interface. E1 Interface gNB-CU-CP to gNB-CU-UP split interface. Service-Based Interfaces SBI service discovery and API-style 5GC communication.
5G Protocols
Browse the 5G protocol stack across PHY, MAC, RLC, SDAP, PDCP, RRC, NAS, NGAP, and related signalling layers.
5G NR PHY Physical layer channels, signals, frame structure, and radio behavior. 5G NR MAC Scheduling, random access, HARQ, and MAC control elements. 5G NR RLC RLC modes, ARQ, PDU formats, timers, and bearer behavior. 5G NR RRC Radio control states, procedures, messages, and mobility. 5G NAS 5GMM, 5GSM, registration, sessions, identities, and causes. NGAP N2 signalling, UE context, PDU sessions, paging, and handover. SDAP QoS flow to DRB mapping and reflective QoS context. RACH / Initial Access Cell discovery, synchronization, PRACH, and early access. Numerology and Subcarrier Spacing SCS, slots, timing, and NR numerology.
5G Messages
Browse searchable 5G protocol message libraries for RRC, NAS, NGAP, F1AP, E1AP, XnAP, and IMS SIP signalling.
5G RRC Messages NR radio-control and system-information messages. 5G NAS Messages 5GMM and 5GSM signalling between UE and core. NGAP Messages N2 messages between gNB and AMF. F1AP Messages CU-DU F1 control-plane messages. E1AP Messages CU-CP to CU-UP E1 control-plane messages. XnAP Messages Inter-gNB mobility and coordination messages. IMS SIP Messages SIP requests and responses for IMS, VoLTE, and VoNR.
5G Call Flows
Study end-to-end 5G signalling procedures for access, registration, security, PDU sessions, mobility, handover, and voice.
Access and Registration Initial access, registration, service request, deregistration, and UE reachability. PDU Session Management Session establishment, modification, release, SSC handling, and user-plane setup. Mobility Procedures Idle mobility, handover, inter-AMF movement, path switch, and continuity. RRC Procedures RRC setup, resume, reconfiguration, release, paging, and radio recovery. Security Procedures Authentication, NAS security, AS security, keys, identity, and security recovery. Voice Call Procedures VoNR, IMS registration, emergency calling, call release, and fallback paths. Network Slice Procedures Slice selection, NSSAI handling, rejection, retry, and slice-aware sessions. QoS Policy Procedures QoS flow setup, modification, release, PCC behavior, and policy enforcement. Data Path Management User-plane establishment, update, release, and session recovery after mobility. Roaming Procedures Visited-network registration, home-routed service, local breakout, and roaming sessions. NTN Procedures Satellite registration, NTN mobility, handover, and timing behavior. Multi-Access Procedures ATSSS steering, switching, splitting, and multi-access continuity.
5G Troubleshooting
Use symptom-led and protocol-led guides to debug registration, access, RRC, PDU session, mobility, throughput, and handover problems.
Registration and Access Failures Access failures, registration rejection, emergency registration, and TAI mismatch. Registration Reject Cause Analysis Interpret NAS reject causes and registration failure branches. AMF Selection and GUAMI Issues Debug AMF selection, GUAMI mismatch, and routing behavior. TAI and Tracking Area Mismatch Find tracking-area and registration-area mismatch problems. Emergency Registration Issues Troubleshoot emergency registration and emergency access behavior. 5G PHY Low Throughput Troubleshooting Radio, MCS, PRB, layer, and scheduling checks for low throughput. RRC Failure Causes Map RRC symptoms to likely radio and procedure causes. PDU Session Establishment Failure Analyze NAS, SMF, policy, and user-plane setup failures.
5G Tools
Access calculators and utilities for radio planning, throughput checks, frequency mapping, and protocol decoding.
NR ARFCN Calculator Convert NR ARFCN values, bands, and frequencies. NR GSCN Calculator Calculate synchronization raster and GSCN values. NR Throughput Calculator Estimate 5G NR downlink and uplink throughput. NR Link Budget Calculator Evaluate coverage and link margin assumptions. 3GPP Decoder Decode protocol-oriented data during trace analysis. NR TBS Calculator Estimate NR transport block size.
5G Releases
Track 5G standards evolution and 5G-Advanced features through release-oriented reading paths.
Release 18 First formal 5G-Advanced baseline. Release 19 Second 5G-Advanced release wave. Release 20 Bridge toward later 5G evolution and early 6G study work. 5G-Advanced Release 18 Practical Release 18 feature summary. NTN Non-terrestrial network access and procedure context. MBS Multicast and broadcast service mapping into radio bearers. Sidelink Sidelink SDAP and SL-DRB mapping context.
FAQ
Quick answers for common 5G reference questions.
Where can I find 5G protocol messages?
Use the 5G Messages hub to browse RRC, NAS, NGAP, F1AP, E1AP, XnAP, and IMS SIP message libraries.
Where can I learn 5G architecture?
Start with the 5G Architecture section for NG-RAN, 5GC, SBA, gNB, AMF, SMF, UPF, and VoNR architecture pages.
Where can I troubleshoot 5G registration or access failures?
Use the 5G Troubleshooting section for registration, access, RRC, NAS, AMF selection, TAI mismatch, and emergency registration issues.
What tools are useful for 5G engineers?
Useful tools include NR ARFCN, GSCN, throughput, link budget, TBS, and 3GPP decoder tools.
Which 5G interfaces are covered?
The site covers N1, N2, N3, N4, N6, N9, NG, Xn, F1, E1, and service-based interfaces.
References
Core reference areas behind the 5G library.
- 3GPP 5G NR and 5G Core protocol specifications
- 5G architecture, interfaces, signalling procedures, and troubleshooting references
- 5G-Advanced release notes and practical engineering tools