Core Network Operator

Description

The term Core Network Operator (CN Operator) refers to an operator that provides services to subscribers as one of multiple serving operators that share at least a radio access network. This definition was introduced in 3GPP Release 6, evolving from the earlier R99/Rel-2 definition of 'Operator that offers core network services.' The concept is central to network sharing architectures, where multiple core network operators can share a common radio access network (RAN) to reduce deployment and operational costs. Each core network operator may provide services to subscribers of other operators through national or international roaming. The core network operator is identified by a Public Land Mobile Network (PLMN) ID, which consists of a Mobile Country Code (MCC) and a Mobile Network Code (MNC).

In a shared network scenario, the radio access network (e.g., UTRAN, E-UTRAN, or NG-RAN) is shared among multiple core network operators. The shared RAN broadcasts multiple PLMN IDs, allowing user equipment (UE) to select the appropriate core network operator. The UE can be registered with one core network operator, but may access services from another through roaming agreements. The core network operator is responsible for managing subscriber data, authentication, authorization, and accounting, as well as providing services such as voice, data, and messaging. The shared RAN provides radio resources and connectivity to the core networks via standardized interfaces (e.g., Iu, S1, N2/N3).

The architecture for network sharing is specified in 3GPP TS 23.251 (Network Sharing; Architecture and functional description). It defines several sharing scenarios, including: (1) Multiple core network operators sharing a single radio access network, (2) Multiple core network operators sharing a single radio access network and a single core network, and (3) Multiple core network operators sharing only parts of the core network. The most common scenario is the first, where the RAN is shared but each operator has its own core network. This allows operators to differentiate their services while benefiting from shared infrastructure.

The core network operator concept is also relevant for national roaming, where a UE of one operator can use the network of another operator when outside its home network coverage. In this case, the visited network's core network operator provides services to the roaming subscriber, with the home network operator handling billing and policy. The core network operator must support the necessary interfaces and protocols for roaming, such as the S6a/S6d interfaces for authentication and the Gx interface for policy control.

The definition of Core Network Operator has remained stable since Rel-6, with only minor wording changes. It is specified in 3GPP TS 21.905 (Vocabulary), TS 22.951 (Service aspects; Service identity and service access; Network selection), and TS 23.251 (Network Sharing). The concept is fundamental to the 3GPP network sharing framework, enabling operators to reduce costs and improve coverage while maintaining separate core networks.

Purpose & Motivation

The Core Network Operator concept was created to support network sharing, a practice that allows multiple mobile operators to share the costs of deploying and operating a radio access network. In the early days of mobile networks, each operator built its own RAN and core network, leading to duplicated infrastructure and higher costs. With the introduction of 3G, regulators and operators sought ways to reduce costs, especially in rural or low-density areas. Network sharing emerged as a solution, and the Core Network Operator concept was defined to formalize the relationship between shared RANs and multiple core networks.

The Core Network Operator concept solves the problem of how to identify and manage multiple operators within a shared network. It allows each operator to maintain its own core network, subscriber base, and services, while sharing the expensive RAN infrastructure. This separation enables operators to compete on services and pricing while cooperating on infrastructure. The concept also facilitates national and international roaming, as the core network operator can provide services to subscribers of other operators. Without this concept, network sharing would be difficult to implement in a standardized way, leading to proprietary solutions and interoperability issues.