Network Identifier

Description

The Network Identifier (NI) is a fundamental component of the Access Point Name (APN), which is a fully qualified domain name (FQDN) used in 3GPP packet core networks to determine the connectivity path for a UE's data session. An APN is structured as two main parts: the Network Identifier (NI) and the Operator Identifier (OI). The NI is the leftmost part of the APN FQDN and is the only mandatory component. It is a label that specifically identifies the external packet data network (PDN) or a specific service within the operator's network that the UE intends to access. Common examples include 'internet', 'ims', 'mms', or a corporate network name like 'companyvpn'. When a UE initiates a Packet Data Protocol (PDP) Context Activation (in 2G/3G) or a PDN Connectivity Request (in 4G/5G), it includes the APN, allowing the network to understand the user's desired destination.

Upon receiving the request, the network element (SGSN in 2G/3G or MME in 4G) uses the APN for DNS resolution. The NI plays the crucial role in this resolution process. The network constructs a DNS query using the APN FQDN to find the IP address(es) of the appropriate Packet Data Network Gateway (PGW in 4G, PCF+UPF in 5G) that serves that specific external network or service. The PGW selection is critical as different PGWs may be dedicated to different services (e.g., one for general internet traffic, another for low-latency IMS voice traffic) or may connect to different external IP networks. The selected gateway then becomes the anchor point for the UE's IP session.

Furthermore, the NI is used in conjunction with subscriber profile information to apply specific policy and charging control (PCC) rules. The network can identify the service being accessed based on the NI and apply corresponding quality of service (QoS) parameters, charging rates, and traffic management policies. For example, traffic from an APN with NI 'ims' will typically be assigned a high-priority QoS class for voice, while 'internet' traffic might have a best-effort class. The NI, therefore, is not just a routing label but also a key for triggering the correct network behavior for a given data session, impacting user experience, billing, and network resource management.

Purpose & Motivation

The Network Identifier concept was created to solve the fundamental problem of routing a mobile user's data session to the correct external network in a scalable and standardized way. In early GPRS networks, as operators began offering access to multiple external networks (e.g., a corporate intranet, a wireless application protocol (WAP) gateway, and the public internet), a mechanism was needed to distinguish between these destinations. Without a standardized identifier, proprietary configurations would have been required, hindering interoperability between UEs and networks from different vendors and operators.

The NI, as part of the APN, provides this standardized lookup mechanism. It abstracts the complex network topology from the UE. The UE only needs to know a logical name (e.g., 'internet'), not the specific IP address of a gateway. This allows operators to change their internal network architecture, upgrade or relocate gateways, and introduce new services without requiring updates to every UE's configuration. It also enables seamless roaming; a visiting UE can use a well-known APN NI (like 'internet' or the roaming partner's IMS APN) to get service, and the visited network's DNS resolution will route the session to the correct local or home-routed gateway based on roaming agreements. The NI is thus a cornerstone of the flexible, service-aware packet core architecture that has evolved from GPRS through to 5G.

Key Features

• Mandatory component of the Access Point Name (APN) FQDN
• Identifies the external Packet Data Network (PDN) or service (e.g., internet, IMS)
• Used for DNS-based selection of the Packet Data Network Gateway (PGW/UPF)
• Triggers specific Policy and Charging Control (PCC) rules and QoS profiles
• Enables service differentiation and network resource allocation
• Supports subscriber roaming through standardized logical names

Evolution Across Releases

Defining Specifications