Service Information

Description

Service Information is a fundamental concept in the 3GPP Policy and Charging Control (PCC) architecture. It represents the collection of application-level parameters that an Application Function (AF) or Network Exposure Function (NEF) provides to the Policy Control Function (PCF) to influence policy decisions for a user's data session. This information is essential for enabling application-aware policy control, where the network can prioritize, charge, or manage traffic based on the specific service being used.

In the 5G Service-Based Architecture (SBA), Service Information is conveyed via the Npcf_PolicyAuthorization service, specifically through the Npcf_PolicyAuthorization_Create or Update operations. The AF/NEF sends a JSON-based request containing the Service Information, which includes details such as the Application Identifier (e.g., 'IMS', 'VoLTE', 'YouTube'), the type of media (audio, video, data), the required bandwidth (both uplink and downlink), and the IP address and port numbers of the media flows. The PCF uses this information to make Policy and Charging Control (PCC) decisions, which are then enforced by the Session Management Function (SMF) and User Plane Function (UPF) via the N4 interface.

Prior to 5G, in the Evolved Packet Core (EPC), Service Information was conveyed from the AF to the Policy and Charging Rules Function (PCRF) over the Rx interface. The PCRF would then combine this with subscription information from the Subscription Profile Repository (SPR) and other network policies to generate PCC rules. These rules were installed on the Policy and Charging Enforcement Function (PCEF) within the Packet Data Network Gateway (PGW). The fundamental concept remained the same: the AF provides application session details, and the policy function translates them into enforceable rules.

The evolution of Service Information reflects the broader architectural shift from EPC to 5G Core. In Rel-15, the definition was updated to reflect the new 5G entities: the AF/NEF, the PCF, and the Npcf_PolicyAuthorization service. This change aligned the terminology with the Service-Based Architecture and introduced the NEF as a potential source of Service Information, enabling third-party applications to interact with the 5G core through a standardized API. The NEF acts as a gateway, authenticating and authorizing external AFs before forwarding their requests to the PCF.

Service Information is critical for several advanced features, including Quality of Service (QoS) enforcement, where the network reserves resources based on the bandwidth requirements; charging, where the operator can apply different tariffs based on the application; and policy control, where the network can block or throttle certain applications. It also enables network slicing, as the PCF can use Service Information to select appropriate slice-specific policies. Without Service Information, the network would treat all traffic equally, unable to differentiate between a voice call and a file download, leading to suboptimal user experience and inefficient resource utilization.

Purpose & Motivation

Service Information exists to bridge the gap between application-layer requirements and network-layer policy enforcement. In early mobile networks (2G/3G), policy control was rudimentary, often based solely on subscription data and static rules. As applications became more diverse and bandwidth-intensive, operators needed a way to dynamically adjust network behavior based on the specific service being used. The Rx interface in EPC (introduced in Rel-8) allowed AFs to provide application session details to the PCRF, enabling real-time policy decisions. This was a significant improvement over static policies, as it allowed the network to prioritize VoLTE calls over best-effort browsing, for example.

However, the EPC approach had limitations. The Rx interface was primarily designed for operator-controlled services (e.g., IMS), and third-party applications had limited access. With the advent of 5G and the Service-Based Architecture, the need for a more open and flexible exposure framework became apparent. The NEF was introduced to allow external AFs to securely interact with the 5G core, and the Npcf_PolicyAuthorization service replaced the Rx interface. Service Information thus evolved to support a wider range of applications and business models, including network slicing, edge computing, and QoS-on-demand.

The concept solves the problem of application-awareness in the network. Without it, the network would be a dumb pipe, unable to differentiate between services. Service Information enables operators to monetize differentiated services, ensure fair usage, and optimize network resources. It also empowers application providers to request specific QoS treatment, leading to better user experience for services like cloud gaming, AR/VR, and industrial IoT.