Description
The Access and Mobility Management Function (AMF) is a fundamental control plane network function (NF) within the 5G Core (5GC) architecture, defined by 3GPP from Release 15 onwards. It serves as the primary termination point for Non-Access Stratum (NAS) signaling, which is the protocol layer between the User Equipment (UE) and the core network, independent of the underlying radio access technology (e.g., NG-RAN, non-3GPP access). The AMF is responsible for a suite of procedures related to UE access and mobility, including initial registration, connection management (establishing and releasing the signaling connection), reachability management (including idle mode mobility and paging), and mobility management (tracking area updates, handovers). It authenticates the UE and authorizes its access to the network, acting as a security anchor by interacting with the Authentication Server Function (AUSF) and the Security Anchor Function (SEAF). A key architectural principle in 5G is the separation of the control plane functions for access/mobility (AMF) and session management (SMF). This decoupling allows the AMF to be selected based on UE location and mobility requirements, while a different SMF can be selected based on the data session's service requirements, enabling greater flexibility, scalability, and support for network slicing.
From a procedural standpoint, when a UE initiates registration with the 5G network, the Radio Access Network (RAN) routes the initial NAS message to an AMF instance. The AMF then orchestrates the UE authentication process. Upon successful authentication and registration, the AMF maintains the UE's context, which includes its identity (SUPI/SUCI), registration status, assigned temporary identifier (5G-GUTI), security context, and the serving SMF(s) for its active Protocol Data Unit (PDU) Sessions. For mobility, the AMF manages the UE's mobility within the 5G system, handling procedures like handovers (with the assistance of other functions) and tracking area updates. It also plays a central role in network slicing by being part of the slice selection process, ensuring the UE is served by the appropriate network slice instance based on its subscription and requested service.
The AMF interfaces with numerous other 5GC NFs. Its key interfaces include N1 (to the UE via the RAN), N2 (to the NG-RAN for control plane signaling), and N11 (to the SMF). It also communicates with the AUSF (N12), Unified Data Management (UDM) (N8), Network Slice Selection Function (NSSF) (N22), and Network Exposure Function (NEF) (N29), among others. This web of interfaces allows the AMF to act as a central hub, coordinating between the UE, the RAN, and other core network functions to manage the UE's access lifecycle. Its stateless design principle, where the UE context can be stored externally in a Unified Data Repository (UDR), enhances reliability and allows for efficient load balancing and redundancy across multiple AMF instances.
Purpose & Motivation
The AMF was created as part of the 5G Core's Service-Based Architecture (SBA) to address the limitations of previous core network architectures, specifically the 4G Evolved Packet Core (EPC). In the EPC, the Mobility Management Entity (MME) combined access, mobility, and session management signaling. This monolithic design limited flexibility, made network function scaling inefficient, and hindered the deployment of diverse services with different requirements on a shared infrastructure. The primary purpose of the AMF is to decouple access and mobility management from session management, a separation that is foundational to 5G's goals of network flexibility, service-based design, and support for network slicing.
By isolating the mobility and connection state management in the AMF, the 5GC can independently scale the AMF and the SMF based on different network loads (e.g., a massive number of idle IoT devices versus high-bandwidth data sessions). This separation directly enables efficient network slicing, as different slices can share a common AMF pool for basic connectivity while utilizing dedicated SMF instances tailored for specific slice performance characteristics (e.g., ultra-low latency, massive IoT). Furthermore, the AMF's design as a stateless function (with context stored externally) improves network resilience, simplifies disaster recovery, and enables more agile load balancing compared to the stateful MME. Its creation was motivated by the need for a core network that could support a vastly wider range of use cases—from enhanced mobile broadband to mission-critical communications and massive IoT—with the required agility, scalability, and efficiency that the previous generation's architecture could not provide.
Architecture
In the Network Map
- Mobile Network → 5G Core → AMF (Packet Controller)
- Mobile Network → NG-RAN → AMF (5G Core (context))
Evolution Lineage
- Evolved from: MME (4G→5G)
- Network evolution overview →
Classification
Release Timeline
Detected Changes Across Releases
from 3GPP Change RequestsSpecific changes extracted from the „Change history“ tables of 3GPP specifications (362 CRs across 5 releases). Complements the general historical overview above with the evidence-based evolution of this function.
In Release 15, the AMF's foundational capabilities were defined, introducing functions for congestion control, load re-balancing for connected UEs, and enhanced mobility management. Key introductions included support for SUCI handling, UE-specific DRX parameter negotiation, and procedures for AMF selection and planned removal notification to the UDM. The release also specified the AMF's role in providing LADN information to the UE and in area of interest reporting for UEs in RRC Inactive state.
- AMF congestion when receiving NAS message TS 24.502CR0051
- UDM receives notification of target/new AMF after AMF planned removal TS 29.503CR0001
- GUTI unique across AMFs in an AMF SET TS 23.501CR0089
- AMF taking both EMC and EMC BS availability into account in setting EMF TS 24.501CR0153
- Revision on AMF transport behaviour of 5GSM message TS 24.501CR0209
- Clarification on UE specific DRX parameter from old AMF to new AMF TS 23.501CR0014
+ 74 more changes
In Release 16, the AMF saw enhancements in several key areas including support for Non-Public Networks (NPN) extensions for Inter-AMF handover, integration into the charging architecture, and new overload control for trusted non-3GPP access. It also gained capabilities for Service Gap control enforcement, handling of Network Identifier (NID) in registration, and improved procedures for AMF discovery and selection using eSBA communication schemas. Furthermore, the release introduced the AMF as a new NF service consumer and expanded its role in location services, event exposure, and 5G SRVCC.
- Updates to AMF procedures for 3rd party trust domain TS 23.222CR0056
- eSBA communication schemas related to AMF discovery and selection TS 23.501CR0804
- AMF overload control for trusted non-3GPP access TS 23.501CR1374
- Service Gap control in 5GS, enforcement in AMF TS 24.501CR0978
- Providing 5G SRVCC Related Subscription to AMF TS 29.503CR0214
- NID in AMF Registration TS 29.503CR0275
+ 77 more changes
In Release 17, the AMF saw enhancements for new network types and services, including support for SNPN mobility, onboarding, and broadcast MBS sessions. Its event exposure capabilities were updated and partitioned, and new services for MBSBroadcast and MBSCommunication were introduced. Furthermore, the AMF received specific functional updates for disaster roaming, satellite LCS, NR RedCap charging, and the handling of parameters like eDRX and routing indicators.
- Selecting the same PCF for AMF and SMF TS 23.501CR2644
- Updating AMF exposed events in TS 23.501. TS 23.501CR2758
- SNPN - SNPN Mobility - AMF selection impacts TS 23.501CR2893
- AMF selection to support UE onboarding SNPN TS 23.501CR2955
- Support of Broadcast MBS Session with an AMF set being deployed TS 23.527CR0056
- AMF handling on NSAC based on EAC mode TS 24.501CR3559
+ 84 more changes
In Release 18, the AMF's functionality was expanded to better support satellite networks by provisioning satellite coverage availability and transferring that coverage data to a UE. Enhancements were also made for service continuity, including improved handling of multicast MBS sessions and restoration of TSS monitoring following an AMF failure. Furthermore, the AMF received updates for mobility and policy enforcement, such as indicating its capability for non-3GPP access path switching and enforcing LADN per DNN & S-NSSAI.
- Reporting the RAN timing synchronization status change from AMF to TSCTSF TS 23.501CR3807
- Transfer of Satellite Coverage Data to a UE and AMF TS 23.501CR3956
- Clarification of AMF behaviour when it receives RFSP Index in Use Validity Time from MME during UE mobility from EPS to 5GS TS 23.501CR3991
- Provisioning Satellite Coverage Availability to the AMF TS 23.501CR4302
- Multicast MBS session (de)activation or update after an AMF failure TS 23.527CR0063
- Restoration of TSS monitoring upon an AMF failure with or w/o restart TS 23.527CR0074
+ 67 more changes
In Release 19, the AMF introduced new capabilities for event exposure, including on-demand broadcast of LCS assistance data, bulk subscriptions at the AMF Set level, and a new event for trajectory tracking during USS changeover. Enhancements were made to support UE positioning and LMF data collection, while new procedures were defined for AMF behavior during policy association deletions and for regenerative payload selection. The release also added an AIoT service API, charging information provisioning, and clarifications for signaling and privacy settings.
- AMF event exposure for supporting on-demand broadcast of LCS assistant data TS 23.501CR5580
- AMF indication of AMF Data Restoration synchronization is initiated TS 23.527CR0092
- AMF behaviour when the AM Policy Association is deleted or does not exist. TS 29.507CR0319
- AMF Set level event exposure Bulk Subscriptions TS 29.518CR1105
- New AMF Event of Trajectory Tracking for USS Change Over TS 29.518CR1135
- Addition of Data Collection parameters in AMF for LMF data collection procedure TS 29.518CR1152
+ 30 more changes
Explore further
Broader topics and technologies where AMF plays a role.
Defining Specifications
3GPP specifications that define or reference AMF, with the latest known release. Sourced from the 3GPP document catalog — see methodology.
| Specification | Title | Release |
|---|---|---|
| TR 21.905 vj00 | 3GPP Technical Terms and Definitions | Rel-19 |
| TS 22.822 vg00 | Satellite Access in 5G Study | Rel-16 |
| TS 23.003 vj50 | Numbering, addressing and identification in 3GPP | Rel-19 |
| TS 23.222 vj80 | Common API Framework for 3GPP Northbound APIs | Rel-19 |
| TS 23.501 vk00 | 5G System Architecture Stage 2 | Rel-20 |
| TS 23.527 vj50 | 5G System Restoration Procedures | Rel-19 |
| TS 23.700 vk00 | XR Services Application Enablement Layer | Rel-20 |
| TR 23.758 vh00 | Study on Edge Application Architecture | Rel-17 |
| TR 23.958 vj00 | EDGEAPP alignment with ETSI MEC and GSMA OP | Rel-19 |
| TS 24.501 vj50 | 5G NAS Protocols Specification | Rel-19 |
| TS 24.502 vj20 | 5G Core Access via Non-3GPP Networks; Stage 3 | Rel-19 |
| TS 24.571 vj20 | Control Plane LCS Procedures | Rel-19 |
| TS 24.890 vg00 | 5G NAS Protocol for 5GS Stage 3 | Rel-16 |
| TS 26.501 vj30 | 5G Media Streaming (5GMS) Architecture | Rel-19 |
| TS 26.804 vj10 | 5G Media Streaming Extensions Study | Rel-19 |
| TS 26.891 vg00 | Media Distribution Services in 5G System | Rel-16 |
| TR 26.919 vj00 | Study on 5G Conversational Media Handling | Rel-19 |
| TR 26.942 vj00 | Study on Media Energy Consumption Exposure & Evaluation | Rel-19 |
| TS 28.204 vi11 | Charging management | Rel-18 |
| TS 28.531 vk00 | Management and Orchestration | Rel-20 |
| TS 28.540 vk10 | 5G Network Resource Model (NRM) Management | Rel-20 |
| TS 28.561 vk00 | Management and Orchestration; Network Digital Twin | Rel-20 |
| TS 28.802 vf00 | Management Study for 5G Network Architecture | Rel-15 |
| TR 28.816 vh00 | Charging for 5G Cellular IoT | Rel-17 |
| TR 28.833 vi01 | Technical Report on 5G LAN-type Service Management | Rel-18 |
| TR 28.840 vi10 | Technical Report | Rel-18 |
| TR 28.843 vi10 | Technical Report on Charging Aspects for Vertical Scenarios | Rel-18 |
| TS 28.874 vj10 | Study on Management Aspects of NTN Phase 2 | Rel-19 |
| TS 28.879 vj10 | OAM for Service Management Exposure Study | Rel-19 |
| TS 29.222 vj40 | Common API Framework (CAPIF) for 3GPP Northbound APIs | Rel-19 |
| TS 29.503 vj50 | UDM Service Based Interface Stage 3 | Rel-19 |
| TS 29.505 vj50 | UDR Service for Subscription Data Usage | Rel-19 |
| TS 29.507 vj40 | 5G Access & Mobility Policy Control Service | Rel-19 |
| TS 29.508 vj40 | 5G Session Management Event Exposure Service | Rel-19 |
| TS 29.509 vj50 | AUSF Service Based Interface Protocol | Rel-19 |
| TS 29.512 vj40 | 5G Session Management Policy Control Service | Rel-19 |
| TS 29.513 vj40 | 5G PCC Signalling Flows & QoS Mapping | Rel-19 |
| TS 29.515 vj50 | Ngmlc Service Based Interface Protocol | Rel-19 |
| TS 29.518 vj50 | AMF Service Based Interface Protocol | Rel-19 |
| TS 29.520 vj40 | 5G Network Data Analytics Services Stage 3 | Rel-19 |
| TS 29.523 vj20 | 5G Policy Control Event Exposure Service | Rel-19 |
| TS 29.524 vj00 | 5G Cause Code Mapping Specification | Rel-19 |
| TS 29.525 vj40 | 5G UE Policy Control Service Stage 3 | Rel-19 |
| TS 29.532 vj30 | MB-SMF Service Based Interface Protocol | Rel-19 |
| TS 29.534 vj20 | 5G Access & Mobility Policy Authorization Service | Rel-19 |
| TS 29.536 vj30 | NSACF Service Based Interface Protocol | Rel-19 |
| TS 29.540 vj40 | Nsmsf Service Based Interface Stage 3 | Rel-19 |
| TS 29.542 vj30 | SMF NIDD Service Based Interface Stage 3 | Rel-19 |
| TS 29.552 vj40 | 5G Network Data Analytics Signalling Flows | Rel-19 |
| TS 29.561 vj30 | 5G Interworking with External Data Networks | Rel-19 |
| TS 29.562 vj40 | HSS Services for IMS & GBA Interworking | Rel-19 |
| TS 29.574 vj40 | 5G Data Collection Coordination Services Stage 3 | Rel-19 |
| TS 29.575 vj40 | 5G Analytics Data Repository Services Stage 3 | Rel-19 |
| TS 29.576 vj40 | 5G Messaging Framework Adaptor Services Stage 3 | Rel-19 |
| TS 29.866 vj00 | IMS Disaster Prevention & Restoration Enhancement | Rel-19 |
| TS 29.890 vg00 | CT3 5G System Technical Report | Rel-16 |
| TS 31.102 vj40 | USIM Application Specification | Rel-19 |
| TS 31.103 vj00 | ISIM Application Specification | Rel-19 |
| TS 32.181 vj00 | User Data Convergence Management Framework | Rel-19 |
| TS 32.240 vj40 | Charging Management Architecture & Principles | Rel-19 |
| TS 32.255 vk10 | Telecom Management; Charging for 5G Data Connectivity | Rel-20 |
| TS 32.256 vj40 | 5G Connection & Mobility Charging Spec | Rel-19 |
| TS 32.272 vj00 | Charging for Push-to-Talk over Cellular (PoC) | Rel-19 |
| TS 32.273 vj00 | MBMS Charging Management | Rel-19 |
| TS 32.278 vj00 | Monitoring Events Offline Charging Specification | Rel-19 |
| TS 32.279 vj00 | 5G MBS Session Converged Charging | Rel-19 |
| TS 32.290 vj50 | 5G Charging for Service Based Interface | Rel-19 |
| TS 32.291 vj40 | Charging Management: Service-Based Interface Protocol | Rel-19 |
| TR 32.847 vi00 | Technical Report | Rel-18 |
| TS 32.899 vf10 | 5G Charging Architecture Study | Rel-15 |
| TS 33.102 vj10 | 3G Security Architecture Specification | Rel-19 |
| TS 33.127 vj50 | Lawful Interception Architecture and Functions | Rel-19 |
| TS 33.401 vj10 | EPS Security Architecture | Rel-19 |
| TS 33.501 vk00 | 5G Security Architecture and Procedures | Rel-20 |
| TS 33.511 vk00 | Security Assurance Specification (SCAS) for gNB | Rel-20 |
| TS 33.514 vk00 | 5G Security Assurance for UDM | Rel-20 |
| TS 33.535 vj00 | 5G AKMA: Authentication and Key Management for Apps | Rel-19 |
| TS 33.701 vj00 | Study on mitigations against bidding down attacks | Rel-19 |
| TR 33.739 vi10 | Study on security enhancement of support for | Rel-18 |
| TR 33.741 vi01 | Home Network Triggered Authentication | Rel-18 |
| TS 33.794 vj10 | Study on Zero Trust Security Enablers for 5G | Rel-19 |
| TS 33.835 vg10 | Study on authentication and key management for apps | Rel-16 |
| TS 33.836 vg10 | Security Study for Advanced V2X Services | Rel-16 |
| TR 33.847 vh10 | 5G Proximity Services Security Study | Rel-17 |
| TS 33.856 vg10 | Security for 5G to 3G Voice Continuity | Rel-16 |
| TS 33.861 vg10 | CIoT Security Evolution for 5G System | Rel-16 |
| TS 33.863 ve20 | Security for Battery-Efficient IoT Device to Enterprise | Rel-14 |
| TS 33.897 vd10 | Security for Isolated E-UTRAN Operation (IOPS) | Rel-13 |
| TS 35.205 vj00 | MILENAGE Algorithm Set: General Overview | Rel-19 |
| TR 35.909 vj00 | 3GPP MILENAGE Algorithm Design Report | Rel-19 |
| TR 35.934 vj00 | Tuak algorithm set for 3GPP auth & key gen | Rel-19 |
| TS 37.473 vj00 | W1 Application Protocol (W1AP) Specification | Rel-19 |
| TS 38.300 vj00 | NG-RAN Overall Description | Rel-19 |
| TS 38.401 vj10 | NG-RAN Architecture Specification | Rel-19 |
| TS 38.410 vj10 | NG Interface Introduction for NG-RAN to 5GC | Rel-19 |
| TS 38.412 vj00 | NG Signalling Transport | 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 |
| TS 38.473 vj10 | 5G F1 Application Protocol (F1AP) | Rel-19 |
| TS 38.811 vf40 | Study on NR Support for Non-Terrestrial Networks | Rel-15 |
