Customized Alerting Tone Service

Description

The Customized Alerting Tone Service (CAT service) is an operator-specific supplementary service defined in 3GPP TS 22.182, with the stage 1 service description provided in TS 22.982. It enables a subscriber to customize the alerting tone that a calling party hears while waiting for the called party to answer. Instead of the conventional network-generated ringback tone, the caller is presented with operator-managed or subscriber-selected content such as music, voice announcements, advertisements, or other audio media. The service is hosted in the network rather than in the terminal, meaning that the calling party requires no special handset support to hear the customized tone.

Architecturally, the CAT service is implemented as an application-layer service that interacts with the circuit-switched and IMS call control domains. When a call is placed to a CAT subscriber, the terminating network detects the subscription and, rather than allowing the normal alerting tone to be generated locally at the calling party's terminal, suppresses that tone and instead establishes a media path from a CAT application server (or equivalent service node) toward the calling party. The CAT server then plays the selected alerting content. This requires coordination between the call control function (MSC server, IMS CSCF, or equivalent) and the CAT application, typically using intelligent network protocols such as CAMEL in the CS domain or SIP-based service invocation in IMS.

Key functional components include the CAT service subscription data stored in the subscriber's profile (HSS/HLR), the CAT application server that stores and streams the customized content, and the call control logic that intercepts the alerting phase and redirects the media. The service must handle the transition from the alerting phase to the conversation phase seamlessly: once the called party answers, the CAT media stream is torn down and the normal speech path between the two parties is established. Operators may also support different CAT content for different callers or time periods, and may allow subscribers to manage their content through web portals, USSD, or IVR interfaces.

The CAT service is closely related to, but distinct from, the Customized Ringing Signal (CRS) service. While CAT customizes what the calling party hears (the alerting tone), CRS customizes what the called party sees or hears as an incoming communication indication. Both are operator-specific services that enrich the basic call experience, and both are typically deployed together in operator service bundles. CAT is primarily an audio experience, though extensions may support multimedia content.

From a standards perspective, the CAT service is described in TS 22.182 (stage 1 and stage 2 aspects) and TS 22.982 (service description). The service has been stable across 3GPP releases from Rel-8 through Rel-19, reflecting its maturity and its continued relevance even as networks migrate toward VoLTE and VoNR. In IMS-based deployments, CAT functionality is realized through SIP-based application servers, and the service must interoperate with supplementary services such as call forwarding, call waiting, and multiparty calling. Charging for CAT is typically subscription-based or content-based, and the service raises considerations around privacy, content licensing, and lawful interception.

Purpose & Motivation

The CAT service exists to give mobile operators a value-added supplementary service that differentiates their offerings and generates additional revenue, while giving subscribers a means of personal expression and branding during call setup. Before CAT, the ringback tone was a purely network-generated signal with no customization potential; every caller heard the same generic tone regardless of whom they were calling. This uniformity represented an untapped service opportunity for operators.

By moving the alerting tone generation into the network and making it subscriber-configurable, CAT solves several problems. It allows operators to monetize the call setup phase through subscriptions, content sales, and advertising. It gives subscribers a personalization channel that works with any calling handset, since the content is played by the network rather than the terminal. It also provides a platform for enterprise branding, where businesses can present a corporate message or jingle to callers.

The service was standardized in 3GPP Rel-8 and has remained essentially unchanged through Rel-19, demonstrating that the original architecture was sound and that the service continues to meet operator and subscriber needs across CS, IMS, and VoLTE/VoNR deployments.