Description
Service Based Interfaces (SBI) represent the core architectural principle of the 5G Core Network (5GC) introduced in 3GPP Release 15. Unlike the 4G EPC's point-to-point interfaces (e.g., S1, S6a), SBI adopts a service-based architecture where each Network Function (NF) (e.g., AMF, SMF, UDM) acts as both a service producer and consumer. These NFs expose their capabilities as standardized, reusable services through Application Programming Interfaces (APIs) that primarily use HTTP/2 with JSON payloads, following RESTful principles. The architecture relies on a Service Based Interface representation, where interactions are defined by service operations (e.g., Nudm_SubscriberDataManagement) rather than circuit-switched signaling. Key components include the Network Repository Function (NRF), which acts as a service registry for NF discovery and registration, and the Service Communication Proxy (SCP) for delegated discovery and load balancing. Communication security is enforced using TLS. How it works: A consumer NF (e.g., SMF) needing a service first queries the NRF (or uses an SCP) to discover the producer NF instance (e.g., UDM). It then directly invokes the producer's API endpoint. This model enables stateless NFs, horizontal scaling, automated lifecycle management, and dynamic network slicing, forming the backbone of a cloud-native, software-defined 5GC.
Purpose & Motivation
SBI was created to address the rigidity, scalability challenges, and slow innovation cycle of the 4G EPC's point-to-point interface model. That model required specific interfaces between each pair of NFs, leading to complex integration, vendor lock-in, and difficulty introducing new services. The shift to 5G demanded an architecture supporting network slicing, edge computing, on-demand scaling, and rapid service deployment. SBI solves these by applying cloud-native and microservices principles to the core network. It enables NFs to be developed, deployed, and scaled independently. The use of standard web protocols (HTTP/2, JSON) allows for easier integration with IT systems, CI/CD pipelines, and third-party applications. This paradigm was motivated by the need for operational agility, support for diverse 5G use cases from massive IoT to critical communications, and the economic imperative of deploying on commercial off-the-shelf hardware in virtualized/containerized environments.
Detected Changes Across Releases
from 3GPP Change RequestsSpecific changes extracted from the „Change history“ tables of 3GPP specifications (154 CRs across 6 releases). Complements the general historical overview above with the evidence-based evolution of this function.
In Release 15, the Service Based Interfaces (SBI) function was newly introduced as the foundational principle for all Control Plane interactions within the 5G Core network, replacing traditional point-to-point interfaces. This release mandated that network functions within the 5GC Control Plane shall only use service-based interfaces for their interactions, enabling a decoupled, scalable architecture. It formally defined key SBI concepts such as NF services, NF instances, and the service-based interface representation, separating User Plane and Control Plane functions for independent evolution.
- Clarification for S-NSSAI based congestion Control TS 23.501CR0072
- SUPI based paging TS 23.501CR0199
- Clarification of S-NSSAI based congestion control TS 23.501CR0295
- Corrections to AF influence (5.6.7) based on CT WG3 LS on AF influence on traffic routing TS 23.501CR0558
- Clarification to the slice based congestion control handling at NG-RAN TS 23.501CR0590
- Priority indication over SBA interfaces via Message Priority header TS 23.501CR0672
+ 5 more changes
In Release 16, the SBI function was enhanced with new capabilities including the introduction of NRF-based P-CSCF discovery and the formal inclusion of IMS-related interfaces within the 5G SBI framework. It also saw the addition of general SBA/SBI security aspects and the implementation of new service-based interfaces for 5G Virtual Network (5G-VN) management. Furthermore, the architecture solidified the principle that control plane network functions shall exclusively use service-based interfaces for their interactions.
- Introduction of NEF based infrequent small data transfer via NAS TS 23.501CR0890
- CR for TS 23.501 based on conclusion of eNA TR 23.791 TS 23.501CR0831
- NRF based P-CSCF discovery TS 23.501CR1035
- QoS monitoring based on GTP-U paths TS 23.501CR1414
- Updating support for subscription-based access restriction TS 29.503CR0282
- Updating support for subscription-based access restriction TS 29.518CR0261
+ 27 more changes
In Release 17, key SBI enhancements included the introduction of SBI-based Short Message Service (SMS) architecture, incorporating the NEF and MNPF, and adding SBI support indications for the IP-SM-GW and SMSF. The release also enabled new discovery and selection procedures, such as NF discovery based on SUCI information and AUSF/UDM discovery based on SUCI. Furthermore, it expanded analytics-driven operations by introducing network slice and UP path selection enhancements based on NWDAF analytics.
- Network Slice restriction based on NWDAF analytics TS 23.501CR2567
- NWDAF discovery and selection based on provided ML models TS 23.501CR2585
- UP path selection enhancement based on analytics info provided by NWDAF TS 23.501CR2586
- Clarification on UE provides PDU Session Pair ID based on URSP rules TS 23.501CR2736
- Thresholds for Priority-based mode TS 23.501CR2744
- IMSI based SUPI support when access an SNPN using credentials owned by CH TS 23.501CR2919
+ 46 more changes
In Release 18, the SBI framework was enhanced to support new services and capabilities including a time synchronization service based on subscription, PCF support for 5GS Packet Delay Variation monitoring exposed to an AF, and PDU Set based handling for both QoS and uplink transmission. It also introduced updates for CN based Mobile-Terminated communication handling, extended DRX for RRC-INACTIVE state, and network-based per UE Network Slice usage behaviour control within the UDM service interfaces. Furthermore, the release added robustness interfaces for the UDM and clarified data exposure via SBI.
- Adding time synchronization service based on subscription TS 23.501CR3762
- PCF support of 5GS Packet Delay Variation monitoring based on QoS monitoring mechanism and exposed to AF TS 23.501CR3792
- Support of PDU Set based handling TS 23.501CR4046
- CN based MT communication capability indication TS 23.501CR4081
- PDU Set based QoS Handling for uplink transmission TS 23.501CR4744
- Compatibility of UDM not supporting SMS SBI TS 23.540CR0013
+ 26 more changes
In Release 19, key enhancements to the Service Based Interfaces (SBI) include the introduction of subscription-based routing to a target core network and the support for I-SMF selection or insertion based on a local offloading allowed indication. Furthermore, the release added MPS priority for Messaging SMS over NAS SBI and introduced CHF discovery and selection based on a CHF Group ID.
- Subscription-based routing to a target core network TS 23.501CR5380
- I-SMF selection/insertion based on local offloading allowed indication TS 23.501CR5604
- Support PDU Set information identification based on MoQ for encrypted XRM traffic TS 23.501CR5632
- Support of Slice change based on AF request TS 23.501CR5764
- I-SMF selection/insertion based on local offloading allowed indication TS 23.501CR5871
- MPS priority for Messaging SMS over NAS SBI TS 23.540CR0020
+ 18 more changes
In Release 20, the SBI function introduced new capabilities for mitigating abnormal user plane traffic based on analytics, as referenced in the Change Request titles. The release also included corrections to the handling of PDU Sets and their associated QoS procedures within the service-based architecture. These updates were implemented within the existing framework where control plane network functions exclusively use service-based interfaces for their interactions.
Explore further
Broader topics and technologies where SBI plays a role.
Defining Specifications
3GPP specifications that define or reference SBI, 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 |
| TS 23.540 vj20 | 5G Service Based SMS Stage 2 | Rel-19 |
| TS 24.186 vj60 | IMS Data Channel applications | Rel-19 |
| TS 24.229 vj50 | IMS call control protocol based on SIP and SDP | Rel-19 |
| TS 26.804 vj10 | 5G Media Streaming Extensions Study | Rel-19 |
| TS 28.203 vi10 | Charging management | Rel-18 |
| TS 29.501 vj40 | 5GC SBI API Design Principles & Guidelines | Rel-19 |
| TS 29.503 vj50 | UDM Service Based Interface Stage 3 | Rel-19 |
| TS 29.518 vj50 | AMF Service Based Interface Protocol | Rel-19 |
| TS 29.543 vj20 | 5G Data Transfer Policy Control Services Stage 3 | Rel-19 |
| TS 29.551 vj30 | 5G PFD Management Service Stage 3 | Rel-19 |
| TS 29.554 vj10 | 5G Background Data Transfer Policy Control Service | Rel-19 |
| TS 29.562 vj40 | HSS Services for IMS & GBA Interworking | Rel-19 |
| TS 29.563 vj30 | TS 29563: Nhss services for HSS-UDM interworking | Rel-19 |
| TS 29.571 vj50 | Common Data Types for 5G Service Based Interfaces | Rel-19 |
| TR 29.829 vh10 | SMS Service-Based Interfaces for 5G Core | Rel-17 |
| TS 32.290 vj50 | 5G Charging for Service Based Interface | Rel-19 |
| TS 33.117 vk00 | Catalogue of General Security Assurance Requirements | Rel-20 |
| TS 33.503 vj20 | Security for Proximity Services (ProSe) in 5G | Rel-19 |
| TS 33.514 vk00 | 5G Security Assurance for UDM | Rel-20 |
| TS 33.529 vj10 | SCAS for SMSF Security Assurance | Rel-19 |
| TS 33.794 vj10 | Study on Zero Trust Security Enablers for 5G | Rel-19 |