Identity / Identifier

Description

In 3GPP specifications, an ID (Identity or Identifier) is a fundamental data element used to uniquely name, label, or address a specific entity within the telecommunications network. This entity can be a user (subscriber), a device (User Equipment), a network node, a service, or a specific session. The concept is pervasive and serves as the cornerstone for network operations, enabling functions such as routing, mobility management, security procedures, and service delivery. Identifiers are defined with specific formats, scopes, and lifetimes, and their management is critical for the network's integrity and functionality.

Architecturally, IDs are embedded within various protocols and interfaces. For instance, in the core network, identifiers like the International Mobile Subscriber Identity (IMSI) or Subscription Permanent Identifier (SUPI) are used for primary subscriber identification. In the Radio Access Network (RAN), identifiers such as the Radio Network Temporary Identifier (RNTI) are assigned dynamically to UEs for efficient radio resource control. The specifications, such as 3GPP TS 25.423 for UTRAN Iur interface user plane protocols, define how these identifiers are carried and interpreted in specific protocol data units (PDUs) to ensure correct inter-node communication and context management.

How an ID works depends on its type. Permanent identifiers, like the IMSI, are stored in the subscriber's SIM card and the network's Home Subscriber Server (HSS) and are used for fundamental procedures like initial attachment and authentication. Temporary identifiers, like the Globally Unique Temporary Identity (GUTI) in 5G, are assigned by the network to protect the user's permanent identity over the air interface and to facilitate efficient paging and service requests. The network constantly maps between different identifiers (e.g., from SUPI to 5G-GUTI) as a user moves or initiates sessions, maintaining state in various network functions like the Access and Mobility Management Function (AMF) in 5G.

Its role is multifaceted. Primarily, it enables unambiguous identification, which is a prerequisite for any communication system. For mobility, IDs allow the network to track a user's location area. For security, they are bound to authentication keys and certificates. For quality of service (QoS), they are linked to specific policy profiles. For charging, they are used to correlate usage records to a specific subscription. The proper handling and protection of identifiers, especially permanent ones, is thus a critical aspect of network security and subscriber privacy.

Purpose & Motivation

The purpose of the ID concept in 3GPP is to provide a standardized, unambiguous method for naming and addressing all entities involved in mobile communication. Without such a foundational system, it would be impossible to route calls and data, authenticate users, manage mobility, or bill for services. It solves the fundamental problem of 'who is who' and 'what is what' in a vast, distributed, and interoperable global network.

Historically, as mobile networks evolved from simple circuit-switched systems to complex IP-based packet-switched architectures, the need for a rich and hierarchical set of identifiers grew. Early systems like GSM introduced the IMSI, which was a breakthrough for global roaming. Each subsequent generation (3G/UMTS, 4G/LTE, 5G) introduced new identifiers and enhanced existing ones to address new requirements such as improved privacy (e.g., using temporary identifiers to mask permanent ones over the radio link), support for heterogeneous network access, and the decoupling of user identity from device identity.

The creation and evolution of identifiers are motivated by key challenges: ensuring global uniqueness to support roaming, enhancing security by minimizing the exposure of permanent identities, improving network efficiency by allowing local, short identifiers for frequent signaling, and enabling new service paradigms like network slicing and massive IoT, where a single user or device may have multiple concurrent identities for different logical networks or services. The ID framework defined across 3GPP specs provides the necessary toolbox for these functions.

Key Features

• Uniqueness within a defined scope (global, network, local)
• Structured format often defined by standards (e.g., MCC, MNC, MSIN for IMSI)
• Support for both permanent (subscription) and temporary (session) identities
• Mapping and correlation between different identifier types by network functions
• Protection mechanisms (e.g., encryption, concealment) for privacy
• Used across all network domains: UE, RAN, Core Network, and external networks

Evolution Across Releases

Defining Specifications