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.
Release Timeline
Detected Changes Across Releases
from 3GPP Change RequestsSpecific changes extracted from the „Change history“ tables of 3GPP specifications (35 CRs across 4 releases). Complements the general historical overview above with the evidence-based evolution of this function.
Studied in Rel-15, normative work from Rel-16.
In Release 16, the specification introduced new foundational aspects for Service Based Interfaces (SBI), including general SBA/SBI principles for security and a defined SBI binding level. It also expanded SBI usage to new functions, such as enabling User Plane Information exposure from the UPF via an SBI and specifying SBI-based SMS procedures for MSISDN-less mobile-originated SMS. Furthermore, the architecture was updated to formally support SBI interfaces for network functions like the AMF and SMF.
In Release 17, the SBI framework was enhanced to support new functionalities including SBI-based SMS with the addition of the NEF and MNPF in its architecture, and the introduction of SBI-based Secondary Authentication and Authorization. It also expanded SBI support to more network functions like the IP-SM-GW, SMSF, HSS for GBA services, and the UPF for user plane information exposure. Furthermore, the release included significant updates to the SBI specification templates, OpenAPI definitions, and data models to improve alignment, readability, and API guidance.
- Alignment of SBI-based SMS TS 23.501CR3660
- Add NEF and MNPF in SBI-based SMS system architecture TS 23.540CR0002
- SBI TS Template Update TS 29.501CR0099
- Add SBI support Indication for IP-SM-GW. TS 29.503CR0864
- Add SBI support Indication for SMSF. TS 29.503CR0865
- HSS GBA SBI Services Definition TS 29.562CR0090
+ 13 more changes
In Release 18, the SBI framework was enhanced to formally include a User Plane Function (UPF) SBI interface within the architecture for event notifications and to clarify procedures for data exposure via SBI. It also introduced support for SBI-based discovery of SMS-related entities and enabled SBI-based Mobile Originated SMS transmission for MSISDN-less users. Furthermore, the release provided updates to SBI documentation templates and addressed the compatibility of the UDM when not supporting SMS over SBI.
- Compatibility of UDM not supporting SMS SBI TS 23.540CR0013
- Adding Redirection clause to SBI template TS 29.501CR0140
- Clarification on Data exposure via SBI TS 23.501CR4935
- Update Architecture for UPF SBI interface TS 23.501CR4937
- Correct SBI stage 3 template for custom operations without resources TS 29.501CR0144
- Update of SBI TS skeleton template TS 29.501CR0149
+ 2 more changes
In Release 19, the key SBI enhancement was the introduction of MPS (Mission Critical Services) priority support for Messaging SMS over NAS via Service Based Interfaces. This builds upon the existing SBI-based SMS architecture defined in earlier releases, specifically impacting the service-based interfaces used for SMS transfer, such as N8 between AMF and UDM. The update ensures that mission-critical SMS messages receive appropriate prioritization when transported over the NAS (N1) reference point using the SBI framework.
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 |
