Description
The UE Reachability Request Parameter for AMF (URRP-AMF) is a signaling parameter used within the 5G Core (5GC) network on the N11 interface between the SMF (Session Management Function) and the AMF (Access and Mobility Management Function). Its primary function is to allow the SMF to explicitly request the AMF to execute UE reachability procedures. This occurs when the SMF receives downlink data for a PDU session belonging to a UE that is in CM-IDLE or CM-CONNECTED with RRC Inactive state, and the SMF determines that a network-triggered service request procedure is required to establish user plane resources.
The parameter is conveyed within the Nsmf_PDUSession_UpdateSMContext service operation request sent by the SMF to the AMF. The URRP-AMF contains specific instructions for the AMF. It typically includes an indication that triggers the AMF to initiate a paging procedure towards the UE's registered area if the UE is in CM-IDLE. For a UE in RRC Inactive state, it prompts the AMF to request the RAN to perform RAN-based paging or to resume the connection. The AMF processes this request, interacts with the (R)AN (Radio Access Network) to locate and contact the UE, and manages the subsequent service request procedure to transition the UE to CM-CONNECTED state and re-establish the user plane path.
Architecturally, the URRP-AMF is a key element in the separation of control plane functions in 5GC. The SMF manages session context but does not handle mobility or reachability—that is the AMF's role. This parameter is the defined mechanism for cross-functional coordination. The AMF, upon successful UE reachability, will update the SMF with the new UE state and, if applicable, the new user plane tunnel information. The parameter may also carry additional context, such as a priority indicator, to influence the paging strategy (e.g., for delay-sensitive services). This ensures efficient and reliable downlink data notification, which is critical for always-on services and applications expecting push notifications.
Purpose & Motivation
URRP-AMF was created to formalize and optimize the interaction between the SMF and AMF for managing UE reachability in the 5G Service-Based Architecture (SBA). In previous architectures like 4G EPC, the SGW handled downlink data notification and triggered paging via the MME, but the functions were more coupled. The 5GC's clear separation of session management (SMF) and mobility management (AMF) required a standardized, service-based interface for this essential coordination.
It solves the problem of how a session-aware function (SMF) can request a mobility-aware function (AMF) to locate a UE without having direct access to mobility states or paging capabilities. Without URRP-AMF, the SMF would be unable to efficiently trigger the re-establishment of user plane connectivity, leading to dropped downlink packets or excessive buffering. This parameter enables efficient, on-demand reachability management, which is vital for power-saving UE states like RRC Inactive and CM-IDLE, as it minimizes unnecessary signaling by triggering paging only when data arrives.
Furthermore, it supports advanced 5G features like network slicing. Different slices may have different requirements for reachability latency. The URRP-AMF mechanism allows the SMF, which is slice-aware, to convey slice-specific reachability priorities or parameters to the AMF, enabling differentiated paging strategies. This addresses the limitation of a one-size-fits-all paging approach and is essential for supporting mission-critical IoT or ultra-reliable low-latency communication (URLLC) services where timely delivery is paramount.
Classification
Detected Changes Across Releases
from 3GPP Change RequestsSpecific changes extracted from the „Change history“ tables of 3GPP specifications (98 CRs across 5 releases). Complements the general historical overview above with the evidence-based evolution of this function.
In Release 15, the URRP-AMF function was introduced to manage UE reachability, particularly by defining the UE-specific DRX parameters negotiated between the UE and AMF and provided to the RAN. This included clarifying how these parameters are handled during mobility, such as being transferred from an old AMF to a new AMF, and their role in the Service Request procedure and when the UE is in CM-CONNECTED with RRC_INACTIVE state. The enhancements ensured the AMF could provide RRC Inactive Assistance Information to the NG-RAN to assist in reachability management and state transitions.
- Clarification on UE specific DRX parameter from old AMF to new AMF TS 23.501CR0014
- UE-specific DRX parameter negotiation between UE and AMF TS 23.501CR0031
- Alignment with TS 23.502 on Service Request procedure TS 23.501CR0034
- Correction to Providing AF request to multiple PCFs TS 23.501CR0161
- Clarification of UE Requested NSSAI TS 23.501CR0168
- UE specific DRX parameters for CM-CONNECTED with Inactive state TS 23.501CR0177
+ 17 more changes
In Release 16, the URRP-AMF function was enhanced to allow the AMF to provide updated **RRC Inactive Assistance Information** to the NG-RAN whenever relevant parameters changed, such as after a **Mobility Registration Update** that modifies the UE's **Registration Area**. This enabled more dynamic RAN-level UE reachability management. Furthermore, the release clarified procedures for **CN based mobile terminated (MT) communication handling** upon network request, impacting how the AMF interacts with the RAN for reactivation.
- Use of NWDAF analytics for decision of MICO mode parameters TS 23.501CR0837
- NEF service for service specific parameter provisioning TS 23.501CR0878
- External parameters provisioning to the 5GS TS 23.501CR0898
- QoS parameters mapping between TSN characters and 5G QoS TS 23.501CR1003
- TSN QoS mapping and 802.1Qbv parameters TS 23.501CR1123
- Extending the significance of the locality parameter TS 23.501CR1312
+ 26 more changes
In Release 17, the URRP-AMF function was enhanced to support Time Sensitive Communication (TSC) and Time Synchronization services requested by an Application Function (AF). This included the introduction of a dedicated architecture for AF-requested TSC support and updates to QoS parameter handling for these services. Furthermore, the release provided clarifications on parameter handling for the Time-Sensitive Networking (TSN) AF and the TSC Traffic Steering Function (TSCTSF).
- Adding some parameters for local NEF selection TS 23.501CR2656
- KI#2 T2: Informative guideline for mapping QoS parameters and DSCP marking TS 23.501CR2718
- Introduction of architecture for AF requested support of Time Sensitive Communication and Time Synchronization TS 23.501CR2833
- Newly added parameters for Local NEF discovery TS 23.501CR2856
- Updates to AF requests to influence traffic routing TS 23.501CR2913
- AF Request for Simultaneous Connectivity over Source and Target PSA at Edge Relocation TS 23.501CR3026
+ 4 more changes
In Release 18, the URRP-AMF function was enhanced to clarify and support network-triggered service requests for a UE in CM-IDLE state with a suspended connection. This update provides specific procedures for the AMF to handle reachability requests when the UE's connection is suspended, ensuring proper mobile-terminated communication handling. The changes also involve the AMF updating RRC Inactive Assistance Information to the NG-RAN when relevant parameters change as a result of NAS procedures.
- Add the default QoS parameters for 5G VN group data TS 23.501CR4010
- Ensuring that a geographical area requested for a time sync service coincides with a RA TS 23.501CR4133
- Update about the Packet Delay Variation description and add PDV in QoS monitoring parameters TS 23.501CR4506
- Clarification on the TSCTSF handling when it receives the time sync request from AF and time sync subscription from UDM TS 23.501CR4514
- Parameters for AF Request Authorization TS 23.501CR4581
- Clarification for GBR and non-GBR support of PDU set QoS Parameters TS 23.501CR4747
+ 14 more changes
In Release 19, the URRP-AMF function was enhanced to support new parameters for AF-requested network slice modification for a UE, including clarifications on the use of the Configured NSSAI and the resolution of the External Identifier. Furthermore, enhancements were made to support AF-requested functionalities for N6 delay measurement, involving corrections to security-related protocol-specific parameters for that procedure.
- Support of Slice change based on AF request TS 23.501CR5764
- AF request and functionalities enhancement to support N6 delay measurement TS 23.501CR5443
- NWDAF discovery and selection parameters TS 23.501CR5978
- Parameters for EIF selection TS 23.501CR5897
- Clarification on UE triggering request for change of QoS TS 23.501CR5960
- Resolution of EN in AF Requested modification of the Set of Network Slice(s) for a UE TS 23.501CR6020
+ 7 more changes
Explore further
Broader topics and technologies where URRP-AMF plays a role.
Defining Specifications
3GPP specifications that define or reference URRP-AMF, 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 |