Network User Access

Description

Network User Access (NUA) is a conceptual term defined in 3GPP specifications, most notably in TS 21.905, which is the vocabulary document for 3GPP. It serves as a standardized label for the overarching process of a user or User Equipment (UE) establishing a connection to a mobile network. While NUA itself is not a specific protocol or architecture, it encompasses the entire suite of procedures, from initial radio contact to authentication and authorization, that culminate in network entry.

The term provides a high-level abstraction for the complex interactions between the UE and the network's Core Network (CN) and Radio Access Network (RAN). It implicitly includes key processes such as cell selection and reselection, random access, registration, and the execution of Non-Access Stratum (NAS) procedures like Attach or Registration. By defining NUA, 3GPP ensures that all subsequent technical discussions about 'access' refer to a consistent and well-understood concept, reducing ambiguity in standards development.

In the network architecture, NUA is not a component but a function that involves multiple network entities. On the UE side, it involves the modem and protocol stack. On the network side, it engages the gNodeB (in 5G) or eNodeB (in 4G) for radio procedures and the Access and Mobility Management Function (AMF) in 5G or the Mobility Management Entity (MME) in 4G for core network procedures like authentication and session establishment. The successful completion of NUA is a prerequisite for any user-plane data transfer or service invocation.

Its role is foundational; without successful Network User Access, no mobile communication service can be delivered. It is the gateway function that validates a user's subscription, establishes their context within the network, and allocates necessary resources. While detailed implementations are specified in other technical specifications (e.g., for NAS and RRC protocols), NUA remains the umbrella term that ties these implementations together under a single, clear objective: granting a user access to the network.

Purpose & Motivation

The primary purpose of defining Network User Access (NUA) as a standardized term is to establish a common vocabulary within the vast ecosystem of 3GPP specifications. Before its formal definition, discussions about 'access' could be interpreted in various ways—radio access, core network access, service access—leading to potential misunderstandings among engineers and standards contributors. By creating a precise term, 3GPP aimed to improve the clarity and consistency of its technical documentation.

Historically, as mobile networks evolved from GSM to UMTS and beyond, the procedures for network entry became increasingly complex, involving more network functions and security steps. There was a need for a high-level concept that could be referenced across different working groups (e.g., RAN, SA, CT) without delving into the implementation specifics of each release. NUA serves this referential purpose, acting as a conceptual anchor point.

It solves the problem of terminological ambiguity. When a specification states that a feature impacts 'Network User Access,' it immediately conveys that the feature affects the initial connectivity phase, potentially involving radio resource control, registration, and authentication. This allows for more efficient specification design and review, as all parties share a baseline understanding of what phase of operation is being discussed. It does not introduce new technology but provides the linguistic framework to describe existing and future access technologies coherently.

Key Features

• Standardized term for network entry procedures
• Encompasses both radio and core network access aspects
• Provides a common reference point in 3GPP documentation
• Abstracts the complexity of underlying protocols like NAS and RRC
• Fundamental prerequisite for any mobile service delivery
• Defined in the 3GPP vocabulary specification TS 21.905

Evolution Across Releases

Defining Specifications