Native SMS in the 5G Core: How PAiCore SMSF Enables Seamless 5G Standalone Messaging

Bringing SMS into the heart of the 5G Standalone architecture

5G Standalone (5G SA) introduces a new network architecture built around the 5G Core (5GC) and its Service-Based Architecture (SBA). Unlike previous mobile network generations, where traditional signalling protocols played a central role, 5G Core network functions communicate through standardized service-based interfaces, primarily using HTTP/2 APIs.

This architectural shift changes how SMS is delivered across the network. For operators deploying 5G SA, ensuring that SMS works reliably from the beginning requires a dedicated messaging function that is designed to operate natively within the 5G Core.

PAiCore’s SMSF Module v1.0.0 addresses this requirement by integrating SMS delivery directly into the 5G Core architecture through standardized 3GPP service interfaces.

Understanding the role of SMSF in the 5G Core

In a 5G Standalone network, several network functions collaborate to support SMS delivery. Each has a defined responsibility within the messaging process.

• Access and Mobility Management Function (AMF): Handles User Equipment (UE) registration and mobility management while providing the connectivity required for SMS signalling.

• Short Message Service Function (SMSF): Provides SMS functionality within the 5G Core, managing the interaction between the AMF and other core network functions.

• Unified Data Management (UDM): Maintains subscriber information and supports SMSF registration and subscriber-related procedures.

• Network Repository Function (NRF): Enables network functions to register their services and discover other available functions.

These functions work together through standardized service-based interfaces, allowing SMS to operate as an integrated service rather than relying on legacy messaging architecture.

Three essential service procedures for 5G SMS

The SMS delivery process depends on several standardized procedures defined within the 3GPP 5G Core architecture. Three are particularly important to SMSF operation.

1. Nsmsf_SMService – Mobile-Originated SMS

The AMF uses the Nsmsf_SMService interface to forward mobile-originated SMS messages from the User Equipment to the SMSF.

This enables the SMSF to receive and process messages originating from subscribers connected to the 5G network.

2. Namf_Communication N1N2MessageTransfer – Mobile-Terminated SMS

For mobile-terminated SMS, the SMSF uses the AMF’s Namf_Communication service, specifically the N1N2MessageTransfer operation, to deliver messages towards the intended User Equipment.

This allows the SMSF to coordinate message delivery through the AMF using the 5G Core service-based architecture.

3. Nudm_UECM – Subscriber Registration

The SMSF uses the UDM’s Nudm_UECM service to register and manage its association with the subscriber.

This procedure supports the registration and management of SMSF-related subscriber context within the 5G Core.

Together, these procedures provide the essential service interactions required to integrate SMS into a standalone 5G environment.

Native 5G integration with PAiCore SMSF

A messaging function designed around legacy interfaces can introduce compatibility challenges when deployed in a modern 5G Core. PAiCore SMSF Module v1.0.0 addresses this by implementing the required service procedures directly through native 5GC service-based interfaces.

The module is designed to interact with the AMF, UDM and NRF, following the architectural principles of the 5G Core.

This approach enables operators to incorporate SMS functionality into their standalone network deployments without treating messaging as an external add-on.

Security built into the architecture

Security is essential when network functions exchange subscriber-related information and messaging requests.

PAiCore SMSF supports TLS 1.3 with mutual TLS (mTLS) authentication configured per gateway. This allows individual gateways to maintain their own security material and authentication boundaries.

By establishing authenticated communication between network functions, the module supports a more controlled and secure service-based environment.

Predictable behaviour under network load

Beyond connectivity and security, operators need predictable behaviour when network functions handle concurrent requests.

PAiCore SMSF includes configurable concurrent-stream limits on its HTTP/2 interfaces, allowing operators to manage the number of simultaneous streams handled by the module.

It also returns 3GPP-compliant ProblemDetails responses when requests cannot be processed. These standardized error responses provide communicating network functions, including the AMF and NRF, with structured information about request failures.

This helps maintain consistency in error handling and supports interoperability across the 5G Core environment.

Building SMS readiness into 5G Standalone deployments

As operators continue expanding their 5G Standalone networks, messaging functionality needs to be considered as part of the core architecture from the beginning.

SMS remains an important mobile service, and its delivery in a 5G SA environment depends on the correct interaction between network functions, standardized service interfaces, secure communication and predictable request handling.

PAiCore SMSF Module v1.0.0 is designed to address these requirements by providing native SMS integration with the AMF, UDM and NRF through the 5G Core service-based architecture.

By building messaging directly into the network architecture, PAiCore helps operators plan for SMS availability from the first day of standalone service.

Explore PAiCore SMSF Module v1.0.0

Discover the module, explore its architecture and access the open-source implementation.

Product Page: https://paicore.tech/platforms/messaging/smsc-smsf/

GitHub Repository: https://github.com/paicoretech/smsf-module

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