Dedicated Core Network Identity

Description

The Dedicated Core Network Identity (DCN-ID) is a unique identifier used in 3GPP networks to distinguish between multiple Dedicated Core Networks (DCNs) that may coexist within a single Public Land Mobile Network (PLMN). A DCN is a core network instance that is dedicated to serve a specific set of subscribers, typically for isolation purposes, customised services, or to support specific business models such as Mobile Virtual Network Operators (MVNOs). The DCN-ID is used by the Radio Access Network (RAN) to select the appropriate core network entity (e.g., MME, SGSN, or AMF) during initial attach or tracking area update procedures.

The DCN-ID is a numeric identifier that is either pre-configured in the UE or provided by the network. When a UE attaches to the network, it may include the DCN-ID in its NAS messages (e.g., Attach Request, TAU Request). The RAN node (eNB, gNB, or RNC) uses this information, along with other parameters such as the UE's subscription information, to route the NAS message to the correct core network node. If the UE does not provide a DCN-ID, the RAN may select a default core network node based on local configuration or load balancing.

The DCN-ID is defined in 3GPP specifications such as TS 23.401 (GPRS enhancements for E-UTRAN), TS 25.401 (UTRAN overall description), TS 25.413 (UTRAN Iu interface RANAP signalling), TS 36.300 (E-UTRAN overall description), TS 36.413 (E-UTRAN S1 application protocol), TS 44.060 (GPRS RLC/MAC), and TS 48.018 (BSS GPRS protocol). These specifications define the format, encoding, and procedures for using the DCN-ID across different radio access technologies (GERAN, UTRAN, E-UTRAN, and NR).

The DCN-ID is typically a 32-bit or 16-bit value, depending on the interface and protocol. For example, in the S1 interface (E-UTRAN to EPC), the DCN-ID is included in the S1AP INITIAL UE MESSAGE as an optional IE. In the Iu interface (UTRAN to GPRS core), it is carried in the RANAP Initial UE Message. The exact encoding and length may vary across releases and access types, but the fundamental purpose remains the same: to allow the RAN to select the correct core network instance.

Dedicated Core Networks are a key enabler for network slicing and multi-tenancy in 5G and beyond. While the DCN concept was originally introduced for 4G (E-UTRAN) and enhanced for 5G, the DCN-ID remains a fundamental identifier for directing UEs to the appropriate core network slice or instance. It allows operators to deploy multiple core networks with different capabilities, policies, and subscriber groups, all sharing the same radio access network. This separation improves security, performance isolation, and service customisation.

In summary, the DCN-ID is a critical identifier that enables the coexistence of multiple dedicated core networks within a single PLMN. It is used during initial access and mobility procedures to ensure that UEs are served by the correct core network instance, supporting operator-specific deployments and network slicing.

Purpose & Motivation

The DCN-ID was introduced to address the need for network operators to deploy multiple dedicated core networks within a single PLMN. Prior to its introduction, all UEs within a PLMN were typically served by a common core network, which limited the ability to provide differentiated services, isolation, or customised network configurations for specific subscriber groups. The DCN-ID solves this problem by allowing the RAN to identify and select the appropriate core network instance for each UE.

This capability is particularly important for supporting Mobile Virtual Network Operators (MVNOs), enterprise customers, and specific vertical industries that require dedicated core network resources. It also enables operators to gradually introduce new core network technologies (e.g., 5G core) while maintaining legacy core networks for existing subscribers. The DCN-ID provides a standardised mechanism for core network selection, ensuring interoperability across different vendors and access technologies.

Furthermore, the DCN-ID laid the foundation for more advanced concepts such as network slicing in 5G, where multiple logical networks are created on a shared infrastructure. By identifying the dedicated core network, the DCN-ID helps ensure that UEs are directed to the correct slice, thereby enabling service differentiation and isolation.