Access Network Identity

Description

The Access Network Identity (ANID) is a critical parameter defined in 3GPP TS 24.302 for Access Network Discovery and Selection Function (ANDSF) management objects and related procedures. It serves as a unique identifier for an access network, allowing the User Equipment (UE) and the network to unambiguously refer to a specific point of attachment. The ANID is not a single, monolithic identifier but rather a structured data type that can contain different types of identities depending on the underlying access technology. For 3GPP access networks, such as GERAN, UTRAN, or E-UTRAN, the ANID typically consists of the Mobile Country Code (MCC), Mobile Network Code (MNC), and a Location Area Code (LAC) or Routing Area Code (RAC) for 2G/3G, or a Tracking Area Code (TAC) for LTE/5G. For non-3GPP access networks, like WLAN, it can be a Service Set Identifier (SSID), a Homogeneous Extended Service Set Identifier (HESSID), or a realm identifier.

Architecturally, the ANID is used within the ANDSF framework to facilitate access network discovery and selection. The ANDSF server, located in the core network, can provide the UE with management objects containing policies and information about available access networks, each identified by its ANID. The UE uses the ANID to match these network-provided policies against the characteristics and identities of the access networks it detects in its radio environment. This matching process is fundamental for implementing network-controlled or UE-assisted traffic steering, routing policies, and seamless mobility between 3GPP and non-3GPP accesses.

In operation, when a UE scans for available networks, it can identify them using their broadcasted identifiers (like PLMN ID, SSID). The UE can map these detected identifiers to the corresponding ANID format. When the UE communicates with the ANDSF server, either by pulling information or receiving pushes, it can report its current or surrounding ANIDs. The ANDSF server then uses these ANIDs to select and deliver the appropriate intersystem mobility policies (ISMP) or inter-APN routing policies (IARP). For instance, a policy might state that for an ANID representing a specific corporate WLAN, all enterprise traffic should be routed via that WLAN, while other traffic uses the cellular connection.

The role of ANID extends beyond ANDSF. It is a foundational element for enabling intelligent access network selection in a multi-access environment. By providing a standardized way to identify any access network, it allows for consistent policy application, accurate network state reporting, and facilitates functions like Access Network Query Protocol (ANQP) in Hotspot 2.0 scenarios. Its structured nature ensures that regardless of whether the network is a 5G NR cell, an LTE eNB, or a Wi-Fi 6 access point, both the network and the UE have a common language to refer to it, which is essential for automation, optimization, and delivering a seamless user experience in heterogeneous networks.

Purpose & Motivation

The ANID was introduced to solve the problem of uniquely and consistently identifying diverse access networks in a multi-access wireless ecosystem. Prior to its standardization, network selection and policy enforcement were largely siloed within individual technology domains (e.g., cellular vs. Wi-Fi). With the convergence of 3GPP and non-3GPP accesses and the drive towards Always Best Connected (ABC) services, there was a pressing need for a common identifier that could be used by network-based policy engines to make intelligent decisions across different radio technologies.

The historical context lies in the 3GPP work on network-based mobility and policy control, particularly with the introduction of the ANDSF in Release 8 as part of the Evolved Packet Core (EPC). ANDSF's purpose was to assist UEs in discovering and selecting access networks. To enable this, a standardized way to 'name' these networks was required. The ANID filled this gap, providing the necessary abstraction layer. It addressed the limitations of previous ad-hoc approaches where network identification was non-interoperable and proprietary, hindering scalable, operator-controlled multi-access traffic management.

Furthermore, ANID enables key use cases like seamless Wi-Fi offloading, traffic steering based on network conditions and subscription policies, and location-based services. By allowing the network to refer to a specific Wi-Fi hotspot or a cellular sector with a precise identifier, operators can deploy sophisticated policies (e.g., 'use this free Wi-Fi ANID for video streaming, but use the macrocell ANID for voice'). It thus became a cornerstone for enabling policy-driven, multi-RAT (Radio Access Technology) mobility and resource optimization in 3GPP networks from EPC through to 5G System (5GS), where non-3GPP integration is even more deeply embedded.