Extended Unique Identifier

Description

The Extended Unique Identifier (EUI) is a generic term for a globally unique identifier used in various networking contexts, including 3GPP mobile networks. In 3GPP specifications, EUI typically refers to identifiers that are based on the IEEE EUI-48 or EUI-64 formats, which are 48-bit or 64-bit identifiers assigned to network interfaces, devices, or other entities. These identifiers are designed to be unique across the entire world, enabling reliable identification and addressing in heterogeneous networks.

In the context of 3GPP, EUI is often used in the context of interworking with non-3GPP access networks, such as Wireless LAN (WLAN) or fixed broadband. For example, in the 5G System (5GS), the UE may be identified by a Subscription Permanent Identifier (SUPI) or a 5G-GUTI, but when accessing via non-3GPP access, an EUI-64 may be used as a MAC address or as part of an identifier for the UE. The EUI can also be used in the core network to identify network functions or interfaces, such as in the case of the N3IWF (Non-3GPP InterWorking Function) or the UPF (User Plane Function).

The EUI is structured according to IEEE standards: an EUI-48 consists of a 24-bit Organizationally Unique Identifier (OUI) assigned by the IEEE, followed by a 24-bit extension identifier assigned by the organization. An EUI-64 extends this to 64 bits, often by inserting a 16-bit value in the middle. This structure ensures global uniqueness and allows for hierarchical allocation. In 3GPP, EUIs are used in various protocols and interfaces, such as in the DHCPv6 protocol for address assignment, or in the EAP authentication framework for identifying supplicants and authenticators.

One of the key roles of EUI in 3GPP is in the area of network slicing and multi-access edge computing, where unique identifiers are needed to distinguish between different devices, slices, or services. EUIs also play a role in security, as they can be used as part of cryptographic key derivation or as identifiers in authentication procedures. For instance, in 5G, the SUCI (Subscription Concealed Identifier) may be derived from a SUPI that includes an EUI, ensuring privacy.

The EUI is defined in 3GPP TS 21.905 (Vocabulary) and referenced in specifications such as TS 23.501 (System Architecture for 5G), TS 24.501 (NAS protocol), and TS 29.571 (5G System; Common Data Types). Its usage is not limited to a single release; it has been present since Release 8 and continues to be relevant in 5G and beyond. As networks evolve towards higher virtualization and heterogeneity, the need for globally unique identifiers like EUI remains critical for interoperability and seamless service delivery.

Purpose & Motivation

The Extended Unique Identifier (EUI) exists to provide a standardized, globally unique identifier for network devices and interfaces, ensuring that no two entities in a network have the same address. This is essential for routing, addressing, and security in any communication system. In 3GPP networks, EUIs are used to identify UEs, network functions, and interfaces, especially when interworking with external networks that rely on IEEE identifiers.

Before the widespread adoption of EUI, various proprietary or locally administered identifiers were used, which could lead to conflicts and interoperability issues. The IEEE EUI standard solved this by introducing a hierarchical allocation scheme with OUIs, guaranteeing uniqueness. 3GPP adopted EUI to facilitate seamless integration with non-3GPP access technologies, such as Wi-Fi and Ethernet, where EUI-48/64 are native identifiers.

In the context of 5G and beyond, EUIs help support features like network slicing, where each slice may need to be uniquely identified, and multi-access edge computing, where devices and services must be distinguishable. They also enable privacy-preserving mechanisms, such as the use of pseudonyms derived from EUIs, to protect user identity. Overall, EUI is a foundational identifier that supports the scalability, interoperability, and security of modern mobile networks.