Next Generation Service Interfaces

Description

Next Generation Service Interfaces (NGSI) are a cornerstone of 3GPP's service-based architecture (SBA), defined primarily for the 5G Core Network (5GC). They represent the standardized Application Programming Interfaces (APIs) that network functions (NFs) use to communicate with each other internally (southbound) and, more importantly, that expose network capabilities and information to authorized external application functions (AFs) northbound. These interfaces are based on HTTP/2 and JSON, utilizing RESTful principles or asynchronous notifications, making them web-friendly and easily consumable by third-party developers. The specifications, such as TS 23.222 and TS 23.722, detail the procedures, data models, and security mechanisms for these interactions.

Architecturally, NGSI operates through a key network function called the Network Exposure Function (NEF). The NEF acts as a secure gateway and policy enforcement point between the 3GPP network and external AFs. When an application needs to access network data (e.g., user location, network status) or request a specific network behavior (e.g., influence traffic routing, configure QoS), it does not communicate directly with core NFs like the PCF or SMF. Instead, it sends API requests to the NEF. The NEF authenticates and authorizes the request, translates the external API call into internal 3GPP signaling (using service-based interfaces like Npcf or Nsmf), and then returns the response back to the AF. This abstraction layer protects the core network and provides a consistent, versioned API regardless of internal network changes.

How NGSI works involves several key procedures. For capability exposure, an AF can subscribe to specific events (e.g., UE reachability status change) and receive notifications when they occur. For service parameter provisioning, an AF can provide expected service parameters to the network, which the policy framework (PCF) can use to make appropriate QoS decisions. The interfaces support both request-response and subscribe-notify paradigms. Key NGSI APIs include Nnef (for external AFs to interact with the NEF) and the internal SBI APIs like Nnrf (NF discovery), Npcf (policy control), and Nudm (unified data management). By providing these standardized interfaces, NGSI enables use cases like edge computing coordination, enhanced quality of experience for applications, and IoT device management.

Purpose & Motivation

NGSI was created to solve the critical problem of 'walled garden' networks where valuable network capabilities and data were inaccessible to third-party service providers. In pre-5G networks, exposing network functions was often done through proprietary, non-standardized gateways, limiting innovation, slowing down service deployment, and creating security risks. The rise of vertical industry applications (e.g., automotive, Industry 4.0, augmented reality) demanded direct, programmable access to network intelligence like location, bandwidth on demand, and latency guarantees.

The motivation for NGSI stems from the need to transition from a monolithic network offering only connectivity to an open platform enabling 'network as a service.' Previous approaches lacked a unified, secure, and scalable exposure mechanism. NGSI, built upon the cloud-native principle of APIs, directly addresses this. It allows mobile network operators to monetize their network assets by offering them as programmable services via open APIs. This fosters an ecosystem where application developers can create services that are deeply integrated with and optimized by the underlying network.

Furthermore, NGSI is essential for fulfilling 5G's promise of supporting diverse vertical industries. An automotive company, for example, can use NGSI APIs to request ultra-reliable low-latency communication (URLLC) slices for its connected vehicles or to obtain real-time vehicular location data for traffic management. Without a standardized exposure framework like NGSI, each vertical would require costly, custom integration projects. NGSI provides the common, reusable, and secure interface layer that makes such integrations efficient and scalable, enabling new revenue streams and innovative services.