Description
The Service Management Function (SMF) is a critical control plane network function within the 5G Core (5GC) architecture, defined by 3GPP. It is responsible for the comprehensive management of Protocol Data Unit (PDU) sessions, which are the logical connections providing user equipment (UE) with connectivity to a data network (DN), such as the internet or an operator service. The SMF interacts with numerous other network functions to perform its duties. During session establishment, the SMF receives session management requests from the Access and Mobility Management Function (AMF). It selects a User Plane Function (UPF) to serve as the data path anchor, allocates an IP address to the UE (acting as a DHCP server or via interaction with an external DHCP server), and establishes the necessary tunnels (e.g., N3, N9 interfaces) between the Radio Access Network (RAN), UPF, and data network. The SMF is also responsible for policy enforcement and QoS control. It interfaces with the Policy Control Function (PCF) to obtain policy rules and then configures the UPF to enforce these rules, such as applying gating, bandwidth limits, and charging triggers. Furthermore, the SMF manages charging data collection by interacting with the Charging Function (CHF). It generates usage reports and forwards them for offline or online charging. The SMF also handles session modification procedures triggered by network policies, user requests, or mobility events (like handovers), ensuring seamless service continuity. It plays a key role in network slicing by being aware of the slice instance and ensuring the PDU session adheres to the specific slice's characteristics and isolation requirements. Its functionality is exposed via service-based interfaces, primarily Nsmf, allowing other authorized NFs to invoke its services.
Purpose & Motivation
The SMF was created as part of the new 5G Core (5GC) service-based architecture (SBA) to address the limitations of the legacy Evolved Packet Core (EPC). In EPC, session management was tightly coupled within the MME (for control plane) and the Serving Gateway (SGW) and PDN Gateway (PGW) for user plane and policy. This monolithic architecture lacked flexibility, scalability, and hindered rapid service innovation. The SMF's purpose is to disaggregate session management into a dedicated, software-based control plane function. This separation allows for independent scaling, more granular policy control, and efficient support for diverse 5G use cases like enhanced Mobile Broadband (eMBB), Ultra-Reliable Low-Latency Communications (URLLC), and massive Machine Type Communications (mMTC). By centralizing PDU session state, the SMF simplifies mobility management, enables advanced features like simultaneous connectivity to multiple data networks, and provides a single point for applying session-specific policies. Its creation was motivated by the need for a cloud-native, agile core network that could dynamically orchestrate connectivity tailored to specific application requirements, which is fundamental to realizing the full potential of 5G, including network slicing and edge computing.
Architecture
In the Network Map
- Mobile Network → 5G Core → SMF (Packet Controller)
Evolution Lineage
- Evolved from: MME (4G→5G), S-GW (4G→5G), PGW (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 (452 CRs across 6 releases). Complements the general historical overview above with the evidence-based evolution of this function.
In Release 15, the SMF was introduced as a new core network function with key responsibilities including PDU session management, QoS flow enforcement, and IP address allocation. Specific new capabilities defined for it involve selecting and managing the UPF, validating UE location for LADN services, and handling inter-system mobility between 4G and 5G. Furthermore, procedures were established for SMF selection based on factors like DNN and network slice, and for its potential collocation with the PGW-C to support EPS interworking.
- SMF QoS mapping TS 29.513CR0010
- Configuration information the UE may exchange with the SMF during the lifetime of a PDU Session TS 23.501CR0003
- Select the same SMF+UPF for PDU sessions of the same DNN within one slice TS 23.501CR0187
- SMF getting UE location from the AMF for NPLI when no QoS Flow to create/Update/modify TS 23.501CR0266
- Clarification on SMF selection TS 23.501CR0275
- How the SMF validates UE location when requested for LADN PDU Session establishment TS 23.501CR0298
+ 30 more changes
In Release 16, the SMF saw significant enhancements primarily centered around the introduction and management of the Intermediate SMF (I-SMF) function. Key new capabilities included I-SMF insertion and change procedures, enabling local traffic switching and UPF-controlled traffic offload, as well as updates to service operations like Create, Retrieve, and Release SM Context to support this architecture. Furthermore, the release introduced mechanisms for SMF selection using analytics and expanded support for the NF Set concept.
- UL CL/BP controlled by I-SMF TS 23.501CR0848
- ATSSS-SMF and UPF selection TS 23.501CR0761
- Use of analytics for SMF selection TS 23.501CR0940
- eSBA communication schemas related to SMF discovery and selection TS 23.501CR0801
- Transfer of N4 information for local traffic switching from SMF to I-SMF TS 23.501CR1050
- Traffic offload by UPF controlled by the I-SMF TS 23.501CR1179
+ 148 more changes
In Release 17, key SMF enhancements included improved support for Edge computing and local access via (I-)SMF discovery and selection based on a Data Network Access Identifier (DNAI), along with procedures for I-SMF and V-SMF restoration. The SMF's role in converged core networks was expanded to support GERAN/UTRAN access and EPS User Plane Integrity Protection when combined with the PGW-C. Furthermore, updates were made for specific scenarios such as handling AN-Requested PDU Session Resource Release, supporting SNPN onboarding, and managing Multicast/Broadcast Service (MBS) sessions during PDU session release.
- KI #1-1, I-SMF selection TS 23.501CR2634
- Selecting the same PCF for AMF and SMF TS 23.501CR2644
- SMF function update to support Edge computing enhancement TS 23.501CR2762
- Support GERAN/UTRAN access in SMF+PGW-C TS 23.501CR2790
- EPS User Plane Integrity Protection using SMF+PGW-C TS 23.501CR3009
- I-SMF/V-SMF Restoration procedure TS 23.527CR0029
+ 101 more changes
In Release 18, key enhancements for the SMF included improved support for 5G Virtual Network (VN) groups with multiple SMF sets and cross-SMF VN group communication. The release also introduced new capabilities for the SMF to make decisions on PDU Set Handling Activation and steering parameters, and to support sending Non-3GPP QoS Assistance Information to the UE. Furthermore, it defined enhancements for V-SMF and I-SMF procedures, including V-SMF selection and change based on target DNAI, and the exchange of specific parameters like PDU set details and ECN marking for L4S between the V/I-SMF and the H-SMF.
- Common EAS re-discovery initiated by SMF TS 23.501CR4144
- Support for 5G VN group with multiple SMF(Set)s TS 23.501CR4306
- KI#4 implementation of cross-SMF VN group communication TS 23.501CR4313
- KI#1 V-SMF selection enhancement to support HR-SBO TS 23.501CR4381
- PCF provides the Periodicity to SMF via PCC rules for resolving the EN for KI#8 TS 23.501CR4529
- SMF to indicate the capability of supporting non-3GPP access path switching TS 24.501CR5314
+ 71 more changes
In Release 19, the SMF saw significant enhancements for **I-SMF based Local Offloading Management**, including new procedures for I-SMF selection/insertion based on a local offloading allowed indication and specific handling at the I-SMF itself, supported by enhancements to the N11, N16a, and N38 interfaces. Furthermore, reliability was improved by allowing PFCP sessions to be excluded from restoration upon an SMF failure within a set and by enabling the provisioning of alternative SMFs per PFCP session.
- P-CSCF triggering SMF/PGW-C failure checking TS 23.380CR0129
- I-SMF selection/insertion based on local offloading allowed indication TS 23.501CR5604
- Local Offloading handling at I-SMF TS 23.501CR5744
- Local Offloading handling at I-SMF TS 23.501CR5825
- PCF's awareness of I-SMF insertion for Local Offloading Management TS 23.501CR5833
- I-SMF selection/insertion based on local offloading allowed indication TS 23.501CR5871
+ 69 more changes
In Release 20, the SMF saw enhancements in charging procedures, including corrections for charging ID uniqueness and handling of the PDU Session ID for V-SMF charging during EPS-5GS interworking. Furthermore, updates were made to the SMF and PCF selection procedures for the UIA_ARC feature. A key architectural development was the delocalization of the SMF to improve local communications within high-density user areas.
Explore further
Broader topics and technologies where SMF plays a role.
Defining Specifications
3GPP specifications that define or reference SMF, with the latest known release. Sourced from the 3GPP document catalog — see methodology.
| Specification | Title | Release |
|---|---|---|
| TS 22.822 vg00 | Satellite Access in 5G Study | Rel-16 |
| TS 23.078 vj00 | CAMEL Phase 4 Stage 2 Specification | Rel-19 |
| TS 23.380 vj10 | IMS Restoration Procedures | Rel-19 |
| TS 23.501 vk00 | 5G System Architecture Stage 2 | Rel-20 |
| TS 23.527 vj50 | 5G System Restoration Procedures | Rel-19 |
| TS 23.558 vk00 | Architecture for Edge Applications | Rel-20 |
| TS 23.700 vk00 | XR Services Application Enablement Layer | Rel-20 |
| TS 24.501 vj50 | 5G NAS Protocols Specification | Rel-19 |
| TS 24.890 vg00 | 5G NAS Protocol for 5GS Stage 3 | Rel-16 |
| TS 26.802 vj20 | Multicast Enhancements for 5G Media Streaming | Rel-19 |
| TR 26.803 vh00 | 5G Media Streaming Extensions for Edge Processing | Rel-17 |
| TS 26.804 vj10 | 5G Media Streaming Extensions Study | Rel-19 |
| TR 26.806 vi00 | Technical Report on Smartly Tethering AR Glasses | Rel-18 |
| 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 28.801 vf10 | Management and Orchestration of Network Slicing | Rel-15 |
| 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 29.061 vj00 | Packet Domain Interworking for PLMN | Rel-19 |
| TS 29.078 vj00 | CAMEL Phase 4 CAP Specification | Rel-19 |
| TS 29.214 vj20 | Policy and Charging Control over Rx | Rel-19 |
| TS 29.244 vj40 | PFCP Specification for Control/User Plane Separation | Rel-19 |
| TS 29.502 vj50 | 5G System; Nsmf Service Based Interface; Stage 3 | 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 29.512 vj40 | 5G Session Management Policy Control Service | Rel-19 |
| TS 29.513 vj40 | 5G PCC Signalling Flows & QoS Mapping | Rel-19 |
| TS 29.514 vj40 | 5G System; Policy Authorization Service; Stage 3 | 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 29.521 vj40 | 5G Binding Support Management Service 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 29.541 vj30 | NEF Service-Based Interfaces for NIDD & SMS | Rel-19 |
| TS 29.542 vj30 | SMF NIDD Service Based Interface Stage 3 | Rel-19 |
| TS 29.551 vj30 | 5G PFD Management Service Stage 3 | Rel-19 |
| TS 29.552 vj40 | 5G Network Data Analytics Signalling Flows | Rel-19 |
| TS 29.558 vj40 | Enabling Edge Applications | Rel-19 |
| TS 29.561 vj30 | 5G Interworking with External Data Networks | Rel-19 |
| TS 29.564 vj50 | Nupf Service Based Interface Protocol | 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 29.585 vj00 | TSN Interworking Protocol for 5G System | Rel-19 |
| TS 29.591 vj40 | 5G NEF Southbound Services Stage 3 | Rel-19 |
| TR 29.820 vh00 | Study on PFCP Best Practice | Rel-17 |
| TS 29.866 vj00 | IMS Disaster Prevention & Restoration Enhancement | Rel-19 |
| TS 29.889 vj10 | Study on UPF data collection for AI/ML | Rel-19 |
| TS 29.890 vg00 | CT3 5G System Technical Report | Rel-16 |
| TS 32.240 vj40 | Charging Management Architecture & Principles | Rel-19 |
| TS 32.255 vk10 | Telecom Management; Charging for 5G Data Connectivity | Rel-20 |
| TS 32.260 vj10 | IMS Charging Management | 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 |
| TS 32.298 vj30 | Charging Data Record (CDR) Parameter Specification | Rel-19 |
| TR 32.847 vi00 | Technical Report | Rel-18 |
| TS 32.899 vf10 | 5G Charging Architecture Study | Rel-15 |
| TS 33.108 vj00 | LI Handover Interface Specification | Rel-19 |
| TS 33.127 vj50 | Lawful Interception Architecture and Functions | 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 33.515 vk00 | 5G SMF Security Assurance Specification | Rel-20 |
| TR 33.739 vi10 | Study on security enhancement of support for | Rel-18 |
| TS 33.749 vj00 | Study on security aspects of edge computing enhancement | Rel-19 |
| TS 33.794 vj10 | Study on Zero Trust Security Enablers for 5G | 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 38.413 vj10 | NG Application Protocol (NGAP) | Rel-19 |
