Radio Access Network sharing

Description

RAN sharing is a network deployment architecture that enables multiple core network (CN) operators to share a common radio access network (RAN). In this model, a single RAN node—such as an eNodeB in LTE, an RNC in UMTS, or a BSC in GSM—is connected to multiple CN nodes that belong to different operators. These CN nodes can include MMEs, SGSNs, and MSC/VLRs, depending on the radio access technology. This allows operators to reduce capital and operational expenditures by sharing the costly RAN infrastructure while maintaining separate core networks and independent service offerings.

The technical realization of RAN sharing involves the RAN node being able to route signaling and user plane traffic to the appropriate CN node based on the subscriber's operator. This is typically achieved through the use of network sharing identifiers, such as the Public Land Mobile Network (PLMN) ID, which is broadcast by the RAN node. When a UE attaches, it selects a PLMN, and the RAN node forwards the connection request to the CN node associated with that PLMN. In E-UTRAN, the eNodeB can be connected to multiple MMEs via S1 interfaces, each belonging to a different operator. Similarly, in UTRAN, the RNC connects to multiple SGSNs and MSC/VLRs via Iu interfaces.

RAN sharing can be implemented in various configurations, including Multi-Operator Core Network (MOCN) and Gateway Core Network (GWCN). In MOCN, the RAN is shared but each operator has its own core network elements. In GWCN, the core network elements are also shared to some extent, with a gateway connecting to multiple operator core networks. The 3GPP specifications, particularly TS 21.905 and TS 22.951, define the requirements and architecture for RAN sharing, ensuring interoperability and standardized procedures.

Key benefits of RAN sharing include reduced deployment costs, faster rollout of new technologies, and improved coverage in rural or low-density areas. It also enables operators to meet regulatory coverage obligations more efficiently. However, RAN sharing introduces challenges such as coordination between operators, security, and ensuring fair resource allocation. 3GPP has developed mechanisms to address these, including differentiated treatment of traffic and isolation of operator-specific data.

In summary, RAN sharing is a crucial enabler for cost-effective network deployment, allowing multiple operators to leverage a single RAN infrastructure while maintaining separate core networks. It is widely used in both developed and emerging markets to optimize network economics and accelerate service availability.

Purpose & Motivation

RAN sharing was introduced to address the high costs associated with deploying and operating radio access networks, especially in scenarios where building separate infrastructure for each operator is economically inefficient. By allowing multiple operators to share the same RAN, it reduces capital expenditure (CAPEX) and operational expenditure (OPEX), making it feasible to extend coverage to rural or underserved areas and to accelerate the deployment of new technologies like 3G, 4G, and 5G.

The concept emerged in the late 1990s (R99) as mobile networks expanded and operators sought ways to reduce costs. Initially, RAN sharing focused on sharing passive infrastructure like towers and sites, but 3GPP standardized active RAN sharing, where the actual base station equipment is shared. This was motivated by the need for more efficient use of spectrum and network resources, as well as regulatory pressures to improve coverage.

Before RAN sharing, each operator had to deploy its own RAN, leading to duplication of infrastructure, higher costs, and slower rollout. RAN sharing solves these problems by enabling a single RAN to serve multiple operators, each with its own core network. This allows operators to focus on differentiating their services at the core and service layers while sharing the expensive radio access. The standardization of RAN sharing in 3GPP ensures interoperability and provides a framework for fair and secure sharing.