Network Sharing

Description

Network sharing is an optional 3GPP feature that enables different core network operators to connect to and share the same radio access network infrastructure. This concept, defined primarily in 3GPP TS 23.251 and referenced in GERAN specifications 43.055, 44.060, and 45.008, addresses the economic and practical need for operators to reduce deployment costs while maintaining separate core network services. The architecture separates the shared radio access network (RAN) from the individual core networks, allowing each operator to retain control over its own subscribers, services, and policies while sharing the expensive radio infrastructure.

When network sharing is active within a given cell, the network broadcasts the PLMN (Public Land Mobile Network) identities of all sharing operators within system information messages. This broadcast mechanism is fundamental to how mobile stations discover and select the appropriate network. A mobile station that supports network sharing reads these multiple PLMN identities during its PLMN selection and reselection processes, then indicates its selected PLMN to the Base Station Subsystem (BSS). This allows the BSS to route the mobile station's traffic to the correct core network operator.

The implementation of network sharing in GERAN (GSM/EDGE Radio Access Network) involves several key components. The shared BSS must maintain associations between PLMN identities and core network nodes, ensuring that signaling and user plane traffic are correctly routed. The system information broadcast must include the necessary PLMN information, and the mobile station must be capable of parsing and acting upon this information. The specifications carefully distinguish between support for GERAN network sharing specifically and support for network sharing on other radio access technologies (RATs), as these are independent capabilities.

From an architectural perspective, network sharing can take several forms. In a Multi-Operator Core Network (MOCN) configuration, multiple core networks connect to a single shared RAN. In a Gateway Core Network (GWCN) configuration, a gateway node sits between the shared RAN and multiple core networks. The GERAN specifications primarily address the MOCN scenario, where the BSS directly connects to multiple core network operators. Each operator's traffic is separated at the BSS level based on the PLMN selected by the mobile station.

The feature has significant implications for network planning, resource allocation, and interference management. Operators sharing a network must coordinate on radio resource management, frequency planning, and capacity allocation. The sharing arrangement can be limited to specific geographic areas or can encompass entire networks. Regulatory considerations also play a role, as national regulators may impose conditions on network sharing to maintain competition. The technical specifications ensure that despite sharing infrastructure, each operator's subscribers receive their subscribed services with appropriate quality of service and security isolation.

Purpose & Motivation

Network sharing was developed to address the substantial capital and operational expenditures associated with deploying and maintaining radio access networks. Building out nationwide RAN coverage requires enormous investment in spectrum, base station equipment, backhaul, and ongoing maintenance. For operators entering new markets, serving rural areas with low population density, or seeking to expand coverage rapidly, the economics of independent network deployment can be prohibitive. Network sharing allows multiple operators to amortize these costs across their subscriber bases while maintaining independent core networks and service offerings.

The feature also addresses regulatory and competitive dynamics in telecommunications markets. Many national regulators encourage or mandate some form of infrastructure sharing to promote competition, reduce environmental impact from duplicate infrastructure, and accelerate coverage in underserved areas. By enabling operators to share RAN infrastructure while competing on services, pricing, and customer experience, network sharing strikes a balance between infrastructure efficiency and market competition.

Before network sharing was standardized, operators wishing to share infrastructure had to rely on proprietary solutions or bilateral agreements that lacked interoperability guarantees. The 3GPP standardization of network sharing, beginning with earlier releases and formalized in Rel-11 for GERAN, provided a common framework ensuring that mobile stations from different vendors could correctly discover, select, and operate on shared networks. This standardization was essential for enabling multi-vendor deployments and ensuring seamless user experience across shared infrastructure.