NGAP Messages
The NG Application Protocol (NGAP) is the core signalling protocol used on the N2 interface between the NG-RAN (gNB) and the 5G Core (AMF). Defined in 3GPP TS 38.413, NGAP enables major control-plane procedures in 5G, including registration, mobility management, PDU session handling, handovers, paging, reset, and overload control.
This page provides a complete NGAP message reference, covering every message defined in the specification with detailed explanations, call flow context, message direction, and Information Element (IE) breakdowns. Whether you are troubleshooting network issues, analyzing logs, or learning 5G signalling, this guide helps you quickly understand how NGAP messages work in real deployments.
- Procedure context and call flow placement
- Message direction and triggering conditions
- Mandatory and optional IEs
- Practical interpretation for engineers and troubleshooting
Use this hub to explore all NGAP procedures from NG Setup and Handover to Configuration Updates, Reset, and Overload handling, and navigate to detailed message-level pages.
Start typing to search message names, slugs, categories, descriptions, and acronyms.
NAS Transport Messages
Initial UE Message, uplink/downlink NAS transport, NAS non-delivery, and reroute NAS handling.
UE Context Management Messages
Initial context setup, UE context modification, release, suspend/resume, RRC inactive reporting, and connection establishment indication.
Mobility Management Messages
Handover preparation, handover resource allocation, path switch, RAN status transfer, and cancellation messages.
PDU Session Management Messages
PDU session setup, modify, release, notify, and session-resource transfer messages.
Paging Messages
Paging, RAN paging, multicast group paging, and paging-related NGAP messages.
Interface Management Messages
NG setup, reset, overload, AMF/RAN configuration updates, and AMF status.
Warning / PWS Messages
Write-replace warning, PWS cancel, restart, and failure indication messages.
UE Radio Capability Messages
Capability information, compatibility check, and capability ID mapping messages.
Trace & Location Reporting Messages
Trace start/deactivation, cell traffic trace, location reporting control, reports, and failure indications.
NRPPa / RIM / RAN Transfer Messages
NRPPa transport, RAN information management, and RAN configuration transfer messages.
Advanced / Usage Reporting Messages
Advanced NGAP reporting messages such as secondary RAT data usage reporting.
FAQ
What are NGAP messages?
NGAP messages are control-plane signalling messages exchanged between NG-RAN and AMF over the NG interface/N2.
Which 3GPP specification defines NGAP?
NGAP is defined in 3GPP TS 38.413.
What is the difference between UE-associated and non-UE-associated NGAP messages?
UE-associated messages relate to a specific UE context. Non-UE-associated messages manage interface-level procedures such as NG setup, reset, overload, configuration, warning, and some transport functions.
What is the difference between NGAP and NAS?
NGAP carries signalling between NG-RAN and AMF. NAS carries UE-to-core signalling and can be transported inside NGAP messages such as Initial UE Message, Uplink NAS Transport, and Downlink NAS Transport.
Why are NGAP messages grouped by procedure?
Grouping by procedure helps engineers scan related messages together, such as NAS transport, UE context, mobility, PDU session, paging, and interface management procedures.
References
- 3GPP TS 38.413 – NG-RAN; NG Application Protocol (NGAP)
- 3GPP TS 38.300 – NR and NG-RAN overall description
- 3GPP TS 23.502 – 5G system procedures