Description
Session Management Congestion Control Experience (SMCCE) is a framework standardized in 3GPP Release 17 to enhance Quality of Service (QoS) by proactively managing congestion within the 5G Core Network's session management layer. It operates by enabling the Session Management Function (SMF) to detect congestion conditions based on network load indicators, such as resource utilization at the User Plane Function (UPF) or within specific network slices. Upon detection, the SMF can apply various mitigation policies, which may include throttling data rates for non-priority sessions, rejecting new session establishment requests for certain services, or triggering network-initiated session modifications to reallocate resources. The framework also defines mechanisms for the SMF to report congestion events to the Policy Control Function (PCF), allowing for dynamic policy adjustments, and to the Network Data Analytics Function (NWDAF) for broader network analytics and optimization.
The architecture of SMCCE is integrated within the existing 5G Service-Based Architecture (SBA). Key interactions involve the SMF, PCF, UPF, and the Access and Mobility Management Function (AMF). The SMF acts as the central controller, receiving congestion-related information from the UPF via the N4 interface, such as buffer occupancy or packet drop rates. Based on pre-configured policies or dynamic instructions from the PCF, the SMF can enforce congestion actions. These actions are applied per PDU Session or per QoS Flow, allowing granular control. For example, the SMF might instruct the UPF to apply a lower Guaranteed Flow Bit Rate (GFBR) for a specific QoS Flow or to mark packets for Explicit Congestion Notification (ECN).
SMCCE's role is critical in maintaining service-level agreements (SLAs), especially for network slicing and ultra-reliable low-latency communication (URLLC) services. By preventing uncontrolled congestion, it helps avoid cascading failures and ensures that mission-critical applications receive the necessary resources. The framework supports both reactive and proactive congestion management, with the NWDAF potentially providing predictive insights to trigger actions before severe congestion occurs. This makes SMCCE a foundational element for automated network management and experience assurance in 5G Standalone (SA) deployments.
Purpose & Motivation
SMCCE was created to address the challenge of maintaining consistent user experience and meeting SLA guarantees in increasingly complex and dense 5G networks. Previous 3GPP releases had congestion control mechanisms, but they were often localized (e.g., in the RAN or at the transport layer) or not tightly integrated with the core network's session and policy control. This could lead to suboptimal decisions, such as a transport node dropping packets without the SMF being aware, preventing intelligent session-level remediation. The motivation for SMCCE stemmed from the need for a holistic, session-aware approach to congestion that aligns with 5G's network slicing paradigm, where different slices have vastly different performance and reliability requirements.
Historically, congestion was often managed with simple queue management (e.g., tail drop) in routers or via radio resource scheduling. These methods lack the application and subscriber context available in the 5G core. SMCCE introduces this context by leveraging the SMF's knowledge of active PDU Sessions, their associated QoS profiles, and the network slice they belong to. This allows for more intelligent actions, like selectively degrading best-effort traffic while protecting a URLLC session for factory automation. The framework solves the problem of opaque congestion where the core network is unaware of bottlenecks in the user plane, enabling coordinated mitigation that can preserve revenue-generating services and overall network stability during traffic surges or partial failures.
Classification
Detected Changes Across Releases
from 3GPP Change RequestsSpecific changes extracted from the „Change history“ tables of 3GPP specifications (115 CRs across 5 releases). Complements the general historical overview above with the evidence-based evolution of this function.
In Release 15, the SMCCE function was newly introduced through corrections to the AF influence traffic steering control and the NWDAF resource. These corrections were implemented within the Session Management Event Exposure Service (Nsmf_EventExposure), which allows NF service consumers like the AF and NWDAF to subscribe to and be notified of PDU session events. The updates ensured proper interaction for traffic steering and analytics data collection as defined for the service.
In Release 16, the SMCCE function was introduced, enabling the Network Data Analytics Function (NWDAF) to collect and provide analytics on service experience and user data congestion. This was achieved by enhancing the Nnwdaf_EventsSubscription and Nnwdaf_AnalyticsInfo services to support subscriptions and notifications for these new analytics events, including service experience variance. Furthermore, the Unified Data Management (UDM) function was newly specified as a consumer of these analytics services provided by the NWDAF.
- Support for Service Experience TS 29.508CR0048
- Support PDU session establishment event TS 29.508CR0068
- Subscribing of service experience for the application TS 29.520CR0031
- Delete the subscription of service experience for the application TS 29.520CR0033
- Notification of service experience for the application TS 29.520CR0034
- Update Nnwdaf_EventSubscription service for service experience TS 29.520CR0048
+ 16 more changes
In Release 17, the SMCCE function introduced new analytics events for Session Management Congestion Control Experience and Redundant Transmission Experience, which are supported for exposure and subscription via the Nsmf_EventExposure service and for analytics provision via the Nnwdaf_AnalyticsInfo and Nnwdaf_EventsSubscription APIs. It also extended User Data Congestion Analytics with new filtering criteria like GPSI and enhanced service experience analytics by adding UPF ID and Application Server Addresses as filters. Furthermore, the NWDAF and DCCF were explicitly added as NF service consumers for these analytics events.
- New event for SM congestion control experience TS 29.508CR0146
- Support Redundant Transmission Experience TS 29.508CR0161
- Provide PDU session information for supporting the UE communication analytics TS 29.508CR0170
- Support UPF information for service experience and DN performance analytics TS 29.508CR0171
- Resolve editor's note on Redundant Transmission Experience event TS 29.508CR0179
- Adding NWDAF as NWDAF services consumer due to analytics aggregation TS 29.520CR0271
+ 46 more changes
In Release 18, the SMCCE function was enhanced by introducing new support for NWDAF-assisted URSPs in Service Experience and for PDU Session Traffic Analytics, which are exposed through the Nsmf_EventExposure service. These additions enable the SMF to provide richer data, such as access type information for a PDU session, to analytics consumers like the NWDAF. Furthermore, the release introduced user consent enhancements and new capabilities for immediate reports and event muting within NWDAF Data Management subscriptions.
- Support NWDAF assisted URSPs in Service Experience TS 29.508CR0215
- Support NWDAF assisted URSPs in Service Experience TS 29.508CR0222
- Support of the Congestion Information Monitoring TS 29.508CR0233
- Supporting data collection for PDU Session Traffic Analytics TS 29.508CR0232
- Collect list of Access Types used for the PDU session from SMF TS 29.508CR0235
- Access type change for MA PDU session update TS 29.508CR0261
+ 24 more changes
In Release 19, the SMCCE function was enhanced with improved RAT Type support for PDU Sessions and received corrections to its Redundant Transmission Experience Analytics. The release also introduced clarifications and corrections to the NWDAF services it relies on, including error handling consolidation for NWDAF APIs and corrections to the NWDAF Analytics Data Model.
- Enhance RAT Type support for PDU Session TS 29.508CR0355
- Clarifications and miscellaneous corrections on NWDAF services TS 29.520CR0984
- Handling of subscription termination due to PDU session release TS 29.508CR0388
- Correction of NWDAF Context resource descripiton TS 29.520CR0939
- RE-NWDAF behaviour when receiving notification flag TS 29.520CR0974
- Corrections to NWDAF Analytics Data Model General clauses TS 29.520CR1062
+ 3 more changes
Explore further
Broader topics and technologies where SMCCE plays a role.
Defining Specifications
3GPP specifications that define or reference SMCCE, with the latest known release. Sourced from the 3GPP document catalog — see methodology.
| Specification | Title | Release |
|---|---|---|
| TS 29.508 vj40 | 5G Session Management Event Exposure Service | Rel-19 |
| TS 29.520 vj40 | 5G Network Data Analytics Services Stage 3 | Rel-19 |