Service Identifier

Description

The Service Identifier is a key concept in 3GPP's policy and charging architecture, defined as an identifier for a service that may designate an end-user service, a part of an end-user service, or an arbitrarily formed group thereof. It plays a central role in flow-based charging and policy control, particularly within the Policy and Charging Control (PCC) framework introduced in later releases. The Service Identifier provides the most detailed level of identification for a service data flow, allowing the network to apply differentiated treatment, charging, and QoS policies to specific traffic flows.

The concept is specified across multiple 3GPP specifications. TS 22.071 defines location services and related identifiers, TS 22.935 covers the service aspects of the IP Multimedia Subsystem (IMS), TS 23.125 addresses flow-based charging in the evolved packet core, TS 23.203 specifies the PCC architecture, TS 23.503 defines policy and charging control for the 5G System, and TS 29.512 specifies the session management policy control service for 5G. This broad specification footprint reflects the Service Identifier's role as a cross-cutting concept that spans service definition, policy enforcement, and charging.

In the PCC architecture, the Service Identifier is used by the Policy and Charging Rules Function (PCRF) in 4G or the Policy Control Function (PCF) in 5G to identify specific service data flows within a Policy and Charging Control (PCC) rule. When an Application Function (AF) provides service information to the PCRF/PCF, it may include a Service Identifier that allows the network to distinguish between different services or different instances of the same service. This enables the network to apply service-specific QoS parameters, charging rates, and gating decisions.

The Service Identifier operates in conjunction with other identifiers in the PCC framework, including the Service Data Flow (SDF) template, the Application Identifier, and the Charging Key. While the Application Identifier identifies the application (e.g., VoIP, video streaming), the Service Identifier provides finer granularity by identifying specific services or service components within that application. For example, a video streaming application might have separate Service Identifiers for the video stream, the audio stream, and the control signaling, each with different QoS and charging requirements.

A concrete instance of a service may be identified if additional AF information is available, as noted in the definition. This means that the Service Identifier alone may not uniquely identify a specific session or flow; additional parameters such as IP addresses, port numbers, or protocol identifiers may be needed to fully resolve the identification. This layered approach allows the network to balance granularity with scalability, applying detailed identification only when necessary and when the required information is available from the AF.

The Service Identifier is particularly important for flow-based charging, where charging is based on the volume, duration, or events associated with specific service data flows rather than on the aggregate traffic of a bearer. This enables operators to offer differentiated pricing for different services, such as zero-rating for specific applications, premium charging for high-priority services, or usage-based billing for data-intensive applications. The Service Identifier ensures that each flow is correctly classified and charged according to the applicable policy.

Purpose & Motivation

The Service Identifier was created to solve the problem of granular service identification in increasingly complex mobile networks. In early GPRS and UMTS networks, charging was primarily based on aggregate data volume per PDP context, with limited ability to distinguish between different types of traffic within the same bearer. As mobile services diversified — encompassing voice, video, gaming, IoT, and enterprise applications — operators needed a mechanism to identify and treat specific service flows differently for charging and policy purposes.

The introduction of flow-based charging in 3GPP Rel-6 marked a paradigm shift from bearer-level to flow-level charging. The Service Identifier became the key enabler of this shift, providing the detailed identification needed to classify individual service data flows. This allowed operators to implement sophisticated charging models, such as charging different rates for different applications, offering free or discounted access to specific services, and applying time-of-day or location-based charging variations.

In the 5G era, the Service Identifier's importance has only grown. With network slicing, edge computing, and ultra-reliable low-latency communications (URLLC), the ability to identify and treat specific service flows with precision is essential for meeting diverse QoS requirements and business models. The Service Identifier, integrated into the 5G PCC framework via TS 23.503 and TS 29.512, enables operators to deliver differentiated services at scale while maintaining fine-grained control over policy and charging.