Identity Information

Description

Identity information is a term used in 3GPP specifications to encompass all data that identifies a user in a communication system. As defined in 3GPP TS 21.905 and referenced in various service and core network specifications (e.g., 22.273, 24.196, 24.407), it includes any information that can be used to identify a user, such as addresses, identifiers, and public identities. The definition explicitly references IETF RFC 2806 (URLs for telephone calls), IETF RFC 2396 (URI generic syntax), and ITU-T Recommendation E.164 (international public telecommunication numbering plan). Identity information can be trusted (generated by the network) or untrusted (generated by the user), reflecting different levels of assurance.

In the context of 3GPP, identity information is crucial for services that require user identification, such as IP Multimedia Subsystem (IMS) services, messaging, and presence. For example, in IMS, a user is identified by one or more Public User Identities (PUIs), which are typically SIP URIs or Tel URIs. These identities are used for routing, authentication, and authorization. The concept of trusted vs. untrusted identity information is important for security: network-generated identities are considered more reliable, while user-generated identities may be spoofed and require verification.

The definition of identity information has evolved over releases. In Release 7, it was defined as "includes all the information (e.g. RFC 2806/RFC2396/E.164) identifying a user, including asserted public identities (network generated) and/or unasserted (user generated) public identities." This wording emphasized the distinction between asserted (trusted) and unasserted (untrusted) public identities. In Release 8, the definition was revised to "all the information (IETF RFC 2806 [11] / IETF RFC 2396 [7] / ITU-T Recommendation E.164 [12]) identifying a user, including trusted (network generated) and/or untrusted (user generated) addresses." This change clarified the terminology, replacing "asserted/unasserted public identities" with "trusted/untrusted addresses," and made the references more precise. The definition has remained essentially unchanged since Release 8, with only minor editorial adjustments.

Identity information is used in various 3GPP specifications. For instance, TS 22.273 (Service requirements for IMS) uses it to define user identities for IMS services. TS 24.196 (IMS emergency sessions) and TS 24.407 (IMS restoration procedures) rely on identity information for session establishment and recovery. TS 24.408 (IMS subscription and notification) and TS 24.416 (IMS multimedia telephony) use it for subscription management and service invocation. TS 24.508 (IMS supplementary services) and TS 24.516 (IMS conferencing) use it for service control. TS 24.607 (IMS message waiting indication) and TS 24.608 (IMS advice of charge) use it for supplementary service interactions. TS 24.616 (IMS communication diversion) uses it for call forwarding. These specifications collectively demonstrate the broad applicability of identity information across IMS and other services.

From a technical perspective, identity information can take many forms: SIP URIs (e.g., sip:[email protected]), Tel URIs (e.g., tel:+1234567890), E.164 numbers, and other address schemes. The trustworthiness of identity information is determined by the network's ability to verify it. For example, a network-generated identity might be derived from the subscriber's SIM credentials, while a user-generated identity might be entered manually and thus less reliable. This distinction is important for security policies, such as blocking calls with spoofed identities or applying different treatment to trusted vs. untrusted identities.

In summary, identity information is a fundamental concept in 3GPP that enables user identification and service delivery. Its definition has evolved to clarify the distinction between trusted and untrusted identities, and it is referenced in numerous specifications for IMS and other services. Understanding identity information is essential for engineers working on user authentication, service invocation, and security in 3GPP networks.

Purpose & Motivation

Identity information exists to provide a standardized way to describe all data that identifies a user in a communication system, particularly in IP-based services like IMS. Before this concept was formalized, different specifications used inconsistent terminology for user identities, leading to confusion and interoperability issues. The term was introduced to unify the description of user identifiers, including addresses, public identities, and other information, and to distinguish between trusted (network-generated) and untrusted (user-generated) identities.

The motivation for defining identity information was the growing complexity of user identification in IMS and other IP-based services. In IMS, a user can have multiple identities (e.g., SIP URIs, Tel URIs) and these can be generated by the network or provided by the user. The network needs to know which identities are trustworthy for authentication, authorization, and billing. By categorizing identities as trusted or untrusted, the network can apply appropriate security policies. For example, a trusted identity might be used for emergency calls, while an untrusted identity might be subject to additional verification.

The concept also addresses the need for a common vocabulary across 3GPP specifications. By defining identity information in TS 21.905 and referencing it in multiple service and core network specifications, 3GPP ensures that all stakeholders have a consistent understanding of what constitutes user identity. This is particularly important for interoperability between different networks and devices. The evolution of the definition from Release 7 to Release 8 refined the terminology, making it clearer and more precise, which reflects the ongoing maturation of IMS and related services.