Terminating Identification Presentation

Description

Terminating Identification Presentation (TIP) is a supplementary service defined by 3GPP that allows the identity of the calling party to be presented to the called (terminating) user. It is part of the family of Calling Line Identification (CLI) services and is specified in a wide range of technical specifications, including 22.173 (IMS Multimedia Telephony), 24.604 (Communication Diversion), and 24.615 (Communication Waiting). TIP operates within the IP Multimedia Subsystem (IMS) and also in circuit-switched networks, providing the terminating user with the calling party's number or SIP URI. The service is typically offered alongside Terminating Identification Restriction (TIR), which allows the calling party to prevent the presentation of their identity.

Architecturally, TIP is implemented through the use of the P-Asserted-Identity and From headers in SIP messages within the IMS. When a call is initiated, the originating network inserts the calling party's identity into the SIP INVITE request. The terminating network, upon receiving the request, verifies the identity and presents it to the called user equipment (UE). The presentation may be subject to authorization checks, such as whether the calling party has subscribed to the service and whether any restrictions apply. In circuit-switched networks, the calling party's number is delivered via the Calling Party Number (CPN) information element in the setup message.

The service is controlled by the terminating user's subscription profile, which is stored in the Home Subscriber Server (HSS) and enforced by the Serving-Call Session Control Function (S-CSCF) in IMS or the Mobile Switching Center (MSC) in CS networks. The TIP service can be activated or deactivated by the user, and its behavior can be influenced by the calling party's TIR settings. For example, if the calling party has invoked TIR, the terminating network may receive an anonymous identity or a presentation indicator set to "restricted," in which case TIP will not display the actual identity.

TIP is closely related to other supplementary services such as Originating Identification Presentation (OIP) and Originating Identification Restriction (OIR). While OIP presents the calling party's identity to the called party, OIR allows the calling party to restrict the presentation of their identity. TIP works in conjunction with these services to provide a comprehensive identity management framework. The service is also applicable to emergency calls, where the calling party's identity may be presented to the emergency services regardless of any restriction settings.

In terms of implementation, TIP relies on the SIP protocol for session establishment and the DIAMETER protocol for authentication, authorization, and accounting (AAA) functions. The service is standardized across multiple releases of 3GPP, ensuring interoperability between different vendors and networks. The specifications 22.173 and 24.604 provide the core requirements and procedures for TIP, while other specs like 24.615 and 24.629 address specific scenarios such as communication waiting and explicit communication transfer. Overall, TIP enhances the user experience by providing essential caller information, enabling call screening, and supporting regulatory requirements for emergency services.

Purpose & Motivation

TIP was created to provide users with the ability to identify incoming callers before answering, a feature that has become fundamental in modern telephony. Before TIP, users had no way of knowing who was calling, which could lead to unwanted calls or missed important communications. The service addresses the need for call screening, allowing users to make informed decisions about whether to answer a call. It also supports regulatory requirements in some regions where emergency services must receive the calling party's identity.

Historically, TIP evolved from the Calling Line Identification Presentation (CLIP) service in traditional circuit-switched networks. As networks migrated to IMS and VoIP, TIP was adapted to work with SIP-based signaling, ensuring continuity of service across different access technologies. The service also had to accommodate privacy concerns, leading to the development of TIR as a complementary service. TIP's design ensures that it can be offered alongside other supplementary services without conflicts, and it is flexible enough to be customized based on user preferences and network policies.

One of the key motivations for TIP was to enable advanced telephony features such as call logs, missed call notifications, and integration with address books. By presenting the calling party's identity, TIP allows user devices to match the incoming number with stored contacts, enhancing the overall communication experience. Additionally, TIP plays a role in fraud prevention by allowing users to verify the authenticity of incoming calls, although additional mechanisms like STIR/SHAKEN are needed for full protection.