Terminating Identification presentation Restriction

Description

Terminating Identification presentation Restriction (TIR) is a supplementary service defined by 3GPP that enables the calling party to prevent the presentation of their identity to the called (terminating) user. It is the counterpart to Terminating Identification Presentation (TIP) and is part of the Calling Line Identification Restriction (CLIR) family of services. TIR is specified in numerous 3GPP technical specifications, including 22.173 (IMS Multimedia Telephony), 24.604 (Communication Diversion), and 24.615 (Communication Waiting). The service operates in both circuit-switched (CS) and IP Multimedia Subsystem (IMS) networks, providing a mechanism for users to maintain privacy when making calls.

In IMS, TIR is implemented through the use of SIP headers and parameters. When a calling party invokes TIR, the originating network sets the presentation indicator in the SIP INVITE request to "restricted" or omits the calling party's identity from the P-Asserted-Identity header. The terminating network, upon receiving the request, checks the presentation indicator and, if restricted, does not present the calling party's identity to the called user. Instead, the called user may see an anonymous indication or no identity information at all. The service is controlled by the calling party's subscription profile, which is stored in the Home Subscriber Server (HSS) and enforced by the Serving-Call Session Control Function (S-CSCF).

TIR can be invoked on a per-call basis or as a permanent subscription setting. The calling party can activate TIR by dialing a specific prefix (e.g., *67 in many networks) or by configuring their user equipment (UE) to always restrict identity presentation. The network then applies the restriction according to the user's preferences and any overriding network policies. For example, emergency calls may override TIR to ensure that the emergency services receive the calling party's identity, as required by regulations in many countries.

The service interacts closely with TIP. When TIR is invoked, the terminating network receives a restricted identity, and TIP will not display the actual calling party's information. However, the terminating network may still receive the calling party's identity for billing or lawful interception purposes, but it is not presented to the user. TIR also works in conjunction with Originating Identification Restriction (OIR), which restricts the presentation of the calling party's identity to the called party in the originating network. Together, these services provide a comprehensive privacy framework.

TIR is standardized across multiple 3GPP releases, ensuring interoperability between different vendors and networks. The specifications 22.173 and 24.604 provide the core requirements and procedures for TIR, while other specs like 24.615 and 24.629 address specific scenarios. The service is essential for users who wish to keep their phone numbers private, such as celebrities, public figures, or individuals concerned about privacy. It also supports regulatory requirements for privacy in many jurisdictions. Overall, TIR is a critical supplementary service that balances the need for caller identification with the user's right to privacy.

Purpose & Motivation

TIR was created to address the privacy concerns of calling parties who do not want their identity revealed to the called party. Before TIR, the calling party's number was always presented to the terminating user, which could lead to unwanted return calls, harassment, or loss of privacy. TIR provides a mechanism for users to control the presentation of their identity, giving them the ability to make calls anonymously when desired. This is particularly important for individuals who need to protect their personal information, such as victims of harassment or public figures.

Historically, TIR evolved from the Calling Line Identification Restriction (CLIR) service in traditional circuit-switched networks. As networks migrated to IMS and VoIP, TIR was adapted to work with SIP-based signaling, ensuring continuity of service across different access technologies. The service also had to accommodate regulatory requirements, such as the need to present the calling party's identity to emergency services even when TIR is invoked. This led to the development of override mechanisms that allow authorized entities to bypass TIR under specific circumstances.

One of the key motivations for TIR was to provide users with a sense of control over their personal information. By allowing users to restrict identity presentation, TIR helps build trust in telecommunication services and encourages users to make calls without fear of their number being misused. Additionally, TIR supports compliance with privacy laws and regulations, such as the General Data Protection Regulation (GDPR) in the European Union, which mandates the protection of personal data. TIR is therefore not only a technical feature but also a legal and ethical necessity in modern telecommunications.