Customized Alerting Tone

Description

The Customized Alerting Tone (CAT) is a service feature that allows the calling party to hear a personalized audio or video content instead of the traditional ringback tone while waiting for the called party to answer. Defined in 3GPP specifications 22.182, 22.982, and 33.106, CAT is an indication customized by the called party or the calling subscriber that is played to the calling party during call establishment or during an established call session. It indicates that the called party is being alerted, the progress of a communication request, or any alerting event during a call session. The CAT may be a piece of recorded or composed music, greeting words, voice, advertisement, or video.

Architecturally, the CAT service is implemented in the core network, typically within the IP Multimedia Subsystem (IMS) or the Circuit Switched (CS) domain. When a call is initiated, the network determines whether the called party has a CAT subscription. If so, instead of generating a standard ringback tone, the network plays the customized content to the calling party. This is achieved through a media server or an application server that stores and streams the CAT content. The CAT can be pre-configured by the subscriber or dynamically selected based on various criteria, such as the calling party's identity, time of day, or location.

The CAT service involves several key components: the CAT application server, which manages the content and plays it to the calling party; the call session control function (CSCF) in IMS, which routes the call and triggers the CAT service; and the media resource function (MRF), which provides the media processing and playback capabilities. In the CS domain, the CAT may be implemented in the Mobile Switching Center (MSC) or a specialized service node. The CAT content is typically stored in a database and can be updated by the subscriber via web or mobile app interfaces.

The CAT service is governed by 3GPP specifications that define the service requirements, architecture, and security aspects. Specification 22.182 outlines the service description and requirements, including user experience, provisioning, and interoperability. Specification 22.982 provides the technical realization, detailing the signaling flows and network entities involved. Specification 33.106 addresses the security and privacy aspects, ensuring that the CAT content is protected and that user privacy is maintained. The service supports both audio and video CAT, with video CAT being more resource-intensive and typically used in IMS with sufficient bandwidth.

From a user perspective, CAT enhances the calling experience by replacing the monotonous ringback tone with personalized content. It can be used for entertainment, advertising, or informational purposes. For example, a subscriber might set a favorite song as their CAT, or a business might use a promotional message. The calling party hears or sees the CAT until the called party answers, at which point the CAT is stopped and the call is connected. If the called party does not answer, the CAT may continue until the call is forwarded to voicemail or the caller hangs up.

The CAT service has evolved over releases, with the definition refined to clarify that it is an indication played during call establishment or an established call session. The initial definition in Rel-8 described it as an Alerting Tone customized by the called or calling subscriber, while the Rel-10 definition expanded it to include the purpose of indicating alerting, progress, or any alerting event. This refinement reflects a broader understanding of the service's role in call progress signaling. The CAT service continues to be supported in subsequent releases, with minor editorial changes.

In terms of implementation, CAT requires coordination between the calling and called parties' networks. If the called party is in a different network, the CAT service must be supported across network boundaries, which may involve interworking agreements. The CAT content is typically played from the called party's network, but it could also be played from the calling party's network if the service is provisioned there. Security measures ensure that the CAT content is not tampered with and that the calling party's privacy is respected.

Overall, the Customized Alerting Tone is a value-added service that leverages core network capabilities to provide a personalized call experience. It demonstrates the flexibility of 3GPP networks in supporting innovative services beyond basic voice communication.

Purpose & Motivation

The Customized Alerting Tone (CAT) service was created to enhance the calling experience by replacing the standard ringback tone with personalized content. Traditional ringback tones are uniform and provide no information other than that the call is progressing. CAT allows the called party (or calling subscriber) to customize what the caller hears, which can be used for entertainment, self-expression, advertising, or conveying information. This adds value for subscribers and can be a revenue source for operators.

Before CAT, the only customization available was the basic ringback tone, which was limited to simple tones or silence. The introduction of CAT in Rel-8 enabled a richer set of media types, including music, voice, and video. This was motivated by the growing demand for personalization and the capabilities of advanced networks like IMS, which can handle multimedia sessions. CAT also serves as a platform for advertisement, allowing businesses to play promotional content to callers.

The CAT service addresses the need for differentiation in a competitive market. Operators can offer CAT as a premium service, and subscribers can choose from a library of content or upload their own. It also provides a way to deliver targeted advertisements, which can be a new revenue stream. The service has evolved to support video CAT, leveraging the high bandwidth of 4G and 5G networks. Security specifications ensure that the content is delivered securely and that user privacy is protected. Overall, CAT enriches the telephony experience and demonstrates the network's ability to support innovative services.