Description
The Next Generation Application Protocol (NGAP) is a critical signaling protocol defined by 3GPP for the interface between the 5G Core Network (5GC) and the Next Generation Radio Access Network (NG-RAN), specifically the gNB or ng-eNB. It operates over the SCTP transport layer on the NG interface (N2 for control plane). NGAP is responsible for all control plane signaling between these two domains, enabling the core network to manage the RAN and vice versa. Its primary functions include the establishment, modification, and release of the UE context in the RAN, which is fundamental for any data or signaling session. NGAP also handles the transfer of Non-Access Stratum (NAS) signaling messages between the UE and the AMF, meaning the RAN transparently relays these messages without interpreting them. Furthermore, it manages UE mobility procedures, such as handovers within the 5G system and from legacy systems, and it supports Paging initiation from the core network. The protocol is designed to be modular and forward-compatible, with a procedure-based model where each elementary procedure (EP) is defined as either Class 1 (requiring a response) or Class 2 (without a response). Key NGAP messages include INITIAL UE MESSAGE, DOWNLINK NAS TRANSPORT, UPLINK NAS TRANSPORT, HANDOVER REQUIRED, and PAGING. Its architecture separates the concerns of user plane management (handled by other protocols on the N3 interface) and control plane signaling, providing a clean, efficient, and scalable mechanism for network control. NGAP is a cornerstone of the 5G Service-Based Architecture (SBA), allowing for flexible network function interaction and enabling advanced features like network slicing by carrying slice information between the RAN and the core.
Purpose & Motivation
NGAP was created to provide a unified, efficient, and future-proof signaling protocol for the 5G system, replacing and enhancing the functionality of protocols like S1-AP from the 4G EPS. The evolution to 5G introduced a new Service-Based Core architecture (5GC) and new RAN requirements, such as support for network slicing, ultra-reliable low-latency communication (URLLC), and massive IoT. The older S1-AP protocol was not designed to natively carry the information elements required for these new services and architectural paradigms. NGAP solves this by being designed from the ground up for 5G, with explicit support for Network Slice Selection Assistance Information (NSSAI), multiple PDU sessions per UE, and differentiated QoS flows. It addresses the limitations of previous approaches by offering greater flexibility, improved efficiency for control signaling, and inherent support for the decoupling of the control and user planes, which is a key tenet of 5G architecture. Its creation was motivated by the need for a protocol that could scale to support a vastly increased number of connected devices, diverse service requirements, and cloud-native network functions, thereby enabling the full vision of 5G.
Classification
Detected Changes Across Releases
from 3GPP Change RequestsSpecific changes extracted from the „Change history“ tables of 3GPP specifications (90 CRs across 6 releases). Complements the general historical overview above with the evidence-based evolution of this function.
In Release 15, NGAP was introduced as the new application protocol for the control plane interface (NG) between the Next Generation Radio Access Network (NG-RAN) and the 5G Core. The foundational specification, TS 38.413, defined its procedures, including Initial Context Setup and the handling of identifiers like the AMF UE NGAP ID. This release also included corrections and clarifications for specific NGAP functions, such as User Plane security handling in Dual Connectivity and the update of Single Network Slice Selection Assistance Information (S-NSSAI) during handovers from EPS to 5GS.
- Fixes for CP protocol stack TS 23.501CR0083
- Clarification on the association of an S-NSSAI to a given application TS 23.501CR0154
- Correction on Control Plane protocol stacks TS 23.501CR0240
- Clarification on Application data TS 23.501CR0242
- Application detection report when the PFDs are removed TS 23.501CR0485
- Correction to TAI list generation TS 23.501CR0488
+ 7 more changes
In Release 16, the NGAP protocol introduced specific enhancements to improve paging efficiency and UE context handling. This included the new capability to provide recommended cells for paging information within the NGAP UE CONTEXT RESUME REQUEST message. Additionally, clarifications and corrections were made to procedures such as the usage of the New AMF UE NGAP ID in the UE CONTEXT MODIFICATION REQUEST message and updates to the UE-TNLA-binding mechanism.
- Protocol stack for W-5GAN support TS 23.501CR0961
- Support of applications with specific QoS hints TS 29.214CR1643
- Correction to protocol stacks for RTT measurements TS 23.501CR1652
- ATSSS PMF Protocol over UDP TS 23.501CR1870
- Remove protocol stack diagrams for IAB TS 23.501CR2003
- Correction on ATSSS rule generation TS 23.501CR2292
+ 11 more changes
In Release 17, NGAP was enhanced to introduce new protocol support for 5G Multicast/Broadcast Services (5MBS) data delivery over the Nmb8 and Nmb9 interfaces. The release also brought specific corrections and clarifications for features like URLLC Redundant PDU Sessions, UE Power Saving, and MBS functionality within the NGAP protocol. Furthermore, it included positioning enhancements for NR and protocol support exchange for NG handover procedures.
- N6mb and Nmb9 protocol to support 5MBS data delivery TS 29.561CR0135
- Nmb8 protocol to support 5MBS data delivery TS 29.561CR0136
- Introduction of NR positioning enhancements to NGAP TS 38.413CR0754
- Exchange of protocol support at target RAN node for NG handover [PROT_SUP] TS 38.413CR0800
- Adding PDU session limitation and protocol stacks for trusted WLAN access for N5CW device TS 23.501CR2991
- 5G URLLC Redundant PDU Session correction for NGAP parameters TS 23.501CR3035
+ 18 more changes
In Release 18, NGAP was enhanced to support new functionalities for assisting application layer operations, including AI/ML and member UE selection. Specifically, the protocol was updated to enable the transfer of mobile IAB authorization state via the DOWNLINK NAS TRANSPORT procedure and to support Quality of Experience (QoE) mobility during NG-based inter-Master Node handovers. Furthermore, corrections and clarifications were made to protocol descriptions, Explicit Congestion Notification (ECN) marking behavior, and the handling of mobility restrictions for Non-Terrestrial Networks (NTN).
- Assistance to Member Selection Functionality for Application Operation TS 23.501CR3910
- 5GS Assistance for Application AI/ML operation: General clause TS 23.501CR3968
- Update NEF to support NWDAF-assisted application detection TS 23.501CR4105
- Update to UE member selection assistance functionality for application operation TS 23.501CR4622
- Translation of Internal-External Information for Assisting Application Layer AI/ML Operations TS 23.501CR4191
- Corrections on NEF(PFDF) support NWDAF-assisted application detection TS 23.501CR4699
+ 16 more changes
In Release 19, NGAP was enhanced with the addition of new procedure texts for XR (Extended Reality) uplink rate control. Furthermore, corrections and clarifications were made to several existing aspects, including the Notification Cause Information Element (IE), procedures related to A-IoT (Ambient IoT), and the overall description of NGAP Services.
- Control Plane and User Plane Protocol stacks involving the MWAB node TS 23.501CR5561
- General description of relaying media related information over N6 using an encapsulation protocol TS 23.501CR5711
- Introduction of NR Femto Architecture and Protocol Aspects TS 38.300CR1035
- Adding per UE per Application level Energy consumption exposure TS 23.501CR6028
- Clarifications on other protocols used for N6 delay measurements TS 23.501CR6331
- Correction on Security related protocol-specific parameters for N6 delay measurement TS 23.501CR6370
+ 7 more changes
In Release 20, the NGAP protocol was enhanced to support the exposure of per-UE application ranking related information by the Exposure Function (EIF), as defined in the new KI#1. This introduces a capability for the NG-RAN to provide application-specific ranking data per user equipment to the core network. This new information facilitates more intelligent network and service management decisions based on application usage context.
- KI#1: Per UE application ranking related information exposed by EIF TS 23.501CR6501
Explore further
Broader topics and technologies where NGAP plays a role.
Defining Specifications
3GPP specifications that define or reference NGAP, with the latest known release. Sourced from the 3GPP document catalog — see methodology.
| Specification | Title | Release |
|---|---|---|
| TS 23.501 vk00 | 5G System Architecture Stage 2 | Rel-20 |
| TS 29.214 vj20 | Policy and Charging Control over Rx | Rel-19 |
| TS 29.561 vj30 | 5G Interworking with External Data Networks | Rel-19 |
| TS 33.836 vg10 | Security Study for Advanced V2X Services | Rel-16 |
| TR 33.847 vh10 | 5G Proximity Services Security Study | Rel-17 |
| TS 38.300 vj00 | NG-RAN Overall Description | Rel-19 |
| TS 38.413 vj10 | NG Application Protocol (NGAP) | Rel-19 |
| TS 38.414 vj00 | NG Interface User Plane Protocol | Rel-19 |
| TS 38.423 vj10 | Xn Application Protocol (XnAP) specification | Rel-19 |