Description
Evolved Mobility Management (EMM) is a core protocol and state management entity defined for the Evolved Packet System (EPS) and continued into the 5G System (5GS). It operates in the control plane between the User Equipment (UE) and the core network's Mobility Management Entity (MME) in 4G or the Access and Mobility Management Function (AMF) in 5G. EMM is responsible for establishing, maintaining, and releasing the mobility management context of a UE, which is essential for the network to know the UE's location (at the tracking/routing area level) and its connection state (EMM-REGISTERED or EMM-DEREGISTERED). This context is crucial for enabling the network to page the UE for incoming sessions and to authenticate the device for network access.
The protocol defines specific EMM procedures, which are initiated by either the network or the UE. Key UE-initiated procedures include the initial Attach, which registers the UE with the network and establishes a default bearer, and the Tracking Area Update (TAU), which updates the network when the UE moves into a new tracking area. Network-initiated procedures include Authentication and Security Mode Control to establish ciphering and integrity protection, and Detach to gracefully remove the UE's context. EMM works in conjunction with the ESM (EPS Session Management) protocol, which handles bearer management; EMM procedures often carry ESM messages as payload.
EMM states are central to its operation. The primary states are EMM-DEREGISTERED, where the UE is not known to the MME/AMF, and EMM-REGISTERED, where a context exists. Within the EMM-REGISTERED state, sub-states like EMM-IDLE and EMM-CONNECTED indicate whether a signaling connection to the radio access network is active. Transitions between these states are triggered by specific events, such as successful attach (deregistered to registered) or connection release (connected to idle). The protocol ensures that security keys are established during registration and are used to protect all subsequent NAS (Non-Access Stratum) signaling messages, providing a secure foundation for mobility management.
Purpose & Motivation
EMM was created as part of the System Architecture Evolution (SAE) in 3GPP Release 8 to provide a unified, IP-based mobility management framework for the new Evolved Packet Core (EPC). Previous 3GPP systems like GPRS and UMTS had mobility management (GMM) that was more tightly coupled with the circuit-switched domain and the legacy network architecture. The purpose of EMM was to design a cleaner, more efficient protocol optimized for all-IP networks, supporting seamless mobility between 3GPP and non-3GPP access networks (like Wi-Fi).
It solved the problem of managing mobility in a flatter network architecture where the control plane (handled by the MME) was separated from the user plane. EMM provides a standardized way for the UE and network to negotiate capabilities, establish security, and maintain location information without the overhead of the older circuit-switched paradigms. Its creation was motivated by the need for higher data rates, lower latency, and simplified network architecture required for LTE, and it laid the groundwork for the mobility management in 5G, where it evolved into the NAS protocol for Registration and Connection Management handled by the AMF.
Classification
Detected Changes Across Releases
from 3GPP Change RequestsSpecific changes extracted from the „Change history“ tables of 3GPP specifications (211 CRs across 5 releases). Complements the general historical overview above with the evidence-based evolution of this function.
Studied in Rel-8, normative work from Rel-15.
In Release 15, EMM was enhanced to support mobility and registration procedures between EPS and 5GS, including the handling of 5GMM parameters like S-NSSAI during these transitions. The release also introduced an extended EMM cause for NB-IoT and provided corrections and clarifications for procedures such as mobility registration updates and the coordination between EMM and 5GMM. Furthermore, it addressed specific scenarios like context management due to service request rejection and the handling of UE radio capability changes in EMM-IDLE mode.
- Handling of S-NSSAI and PDU session ID during mobility between EPS and 5GS TS 24.301CR2965
- Extended EMM cause for NB-IoT TS 24.301CR3035
- 5GMM parameter handling for TAU rejected with EMM cause #9 TS 24.301CR3047
- Correction of inconsistency in EMM timers table TS 24.301CR2897
- Correction to EMM/GMM coordination TS 24.301CR2981
- Non-semantical mandatory information element errors for EMM TS 24.301CR3050
+ 26 more changes
In Release 16, the EMM function introduced new support for mobility to and from NB-IoT, including paging across multiple carriers, and enhanced inter-RAT mobility procedures between E-UTRAN and 5GS. It also added specific procedures and information storage for RLOS (Reduced Latency and Overhead State) and defined mechanisms for the transfer of port management information containers, MAC addresses, and DS-TT residence time via NAS signaling. Furthermore, the release provided clarifications for EMM cause codes in service reject messages and enhanced security handling for TAU requests during mobility between S1 and N1 interfaces.
- Adding the stage 3 detail on EMM substates for attaching for access to RLOS. TS 24.301CR3179
- Mobility handling for UEs attached to access RLOS TS 24.301CR3192
- RLOS storage of EMM information TS 24.301CR3268
- Types of EMM procedures for RLOS TS 24.301CR3269
- UE radio capability ID availability indication at mobility TAU TS 24.301CR3283
- Inter-RAT mobility to and from NB-IoT in 5GS TS 24.501CR0989
+ 63 more changes
In Release 17, enhancements to Evolved Mobility Management (EMM) included clarifications for mobility management based on Network Slice-Specific Authentication and Authorization (NSAC) per access type and for roaming cases. Other updates provided specific UE behaviour clarifications for various EMM cause values and procedures, such as handling Authentication and Key Management for Applications (AKMA) impact and recovering service on NR after a network-triggered detach. Additionally, procedures were refined for scenarios like mobility Tracking Area Updates (TAU) outside the current Registration Area and for onboarding in Standalone Non-Public Networks (SNPN).
- Handling of reject cause #78 in EMM procedures TS 24.301CR3620
- The impact on UE due to the introduction of Authentication and Key Management for Applications (AKMA) TS 24.501CR2794
- Inter-network mobility TS 24.501CR3206
- Onboarding in SNPN - mobility registration update TS 24.501CR3211
- Clarify mobility management based on NSAC per access type independently TS 24.501CR3516
- Clarification of mobility management based NSAC for roaming case TS 24.501CR3515
+ 37 more changes
In Release 18, EMM enhancements focused on managing UEs with discontinuous coverage, introducing mechanisms for UE unavailability period reporting and clarifying EMM states and procedures for such scenarios. It also added support for mobility management and policy procedures related to temporarily available network slices and equivalent SNPNs. Furthermore, the release provided clarifications and corrections to various EMM procedures, including attach after IRAT, detach initiation conditions, and congestion control interactions.
- Support of mobility management and power saving with discontinuous coverage TS 23.401CR3721
- UE unavailability period reporting for enhanced discontinuous coverage overrides mobility management congestion control - EPS TS 24.301CR3939
- Transport of messages of network-requested UE policy management procedure TS 24.301CR3934
- Equivalent SNPNs usage for mobility TS 24.501CR4836
- Mobility management for the support of optimised handling of temporarily available network slices TS 24.501CR5176
- Clarification about the condition of the PCF initiating the Network-requested UE policy management procedure TS 24.501CR5430
+ 31 more changes
In Release 19, the EMM function was enhanced with specific procedural clarifications and error handling improvements. Key updates included refined behaviors for NAS signalling connection release upon receiving specific EMM causes, such as cause #83, and corrections for handling invalid EPS bearer identities within the EMM TRANSPORT message's Data container. Furthermore, the release introduced support for sending the ESM TRANSPORT Message while in EMM-IDLE mode with a suspend indication and provided clarifications on EMM procedures during NAS congestion and state management when a UE returns to coverage.
- Update EMM procedures to support the storage of the information TS 24.301CR4159
- NAS signalling connection release after EMM cause 83 TS 24.301CR4402
- Handling of inactive PDP context in EMM TRANSPORT message TS 24.301CR4517
- Alignment of EMM Transport message TS 24.301CR4459
- Invalid EPS bearer identity in the Data container IE in the EMM TRANSPORT message TS 24.301CR4494
- Inclusion of ATSSS status in related session management messages TS 24.501CR6880
+ 24 more changes
Explore further
Broader topics and technologies where EMM plays a role.
Defining Specifications
3GPP specifications that define or reference EMM, with the latest known release. Sourced from the 3GPP document catalog — see methodology.
| Specification | Title | Release |
|---|---|---|
| TS 23.401 vj50 | Evolved Packet System (EPS) Stage 2 Description | Rel-19 |
| TS 24.301 vj60 | NAS protocol for Evolved Packet System | Rel-19 |
| TS 24.501 vj50 | 5G NAS Protocols Specification | Rel-19 |
| TS 24.801 v810 | CT1 SAE NAS Aspects for EPC | Rel-8 |
| TS 24.890 vg00 | 5G NAS Protocol for 5GS Stage 3 | Rel-16 |
| TS 26.851 vb20 | Enhancements to Multimedia (EMM) for PSS, MMS, MBMS | Rel-11 |
| TS 31.121 vi50 | UICC-terminal interface test specification | Rel-18 |
| TS 33.401 vj10 | EPS Security Architecture | Rel-19 |
| TS 36.300 vj00 | E-UTRAN Radio Interface Protocol Architecture Overview | Rel-19 |
| TS 36.401 vj00 | E-UTRAN Overall Architecture Description | Rel-19 |
| TS 36.509 vh40 | EPC Special UE Conformance Testing Functions | Rel-17 |