By Qun Wei (Rapporteur), Tianqi Xing (Rapporteur), Zelin Wang and Chenyi Li (both: China Unicom Research Institute)

First published December 2024, in Highlights Issue 09

3GPP has just selected Indirect Network Sharing (INS) as the next evolutionary step for 5G-Advanced Rel-20, at the recent Melbourne TSG SA plenary (TSGs#105). This follows a big year for the technology in 2024, where INS was commercially deployed - as a Rel-19 technology.

Indirect Network Sharing is specified in 3GPP TS 22.261, TS 23.501 and TS 23.502, allowing the communication between the shared RAN and the core network of the participating operator to be routed through the core network of the sharing parties, as one of the key pragmatic measures of 5G Network Co-Construction and Sharing.

Examples of INS scenarios include; wide-range coverage of rural areas, long-distance road coverage, compatibility with existing networks, service consistency and cooperation with diverse networks.

With INS, the communication between the Shared NG-RAN and the participating parties’ core network happens via a number of inter-network interfaces that are independent of the actual number of base stations at the shared NG-RAN.

Motivation

INS is designed to support the capability for users to access another operator's 5G networks when outside their own operator 5G coverage, enabling the continuous use of 5G services. It can significantly improve 5G network resource utilization, 5G network coverage in remote areas, 5G services user experience, and promote the high-quality development of the communication infrastructure.

Operators have deployed 5G access networks and core networks with a Multiple Operator Core Network (MOCN). The challenge for the network operators is the maintenance generated by the interconnection (e.g., number of N2 and N3 interfaces) between the shared RAN and two or more participating operators’ core networks, especially for a large number of shared base stations.

For these reasons, it is valuable to introduce a newly supported network sharing scenario.

By agreeing to build a shared network together - to cover the entire country - multiple operators can share one NG-RAN while their 5GCs are independently operated, without mandatory direct connectivity of the shared NG-RAN to the core networks of the other participating operators (as per Figure 2).

For users, the network services can still be transparent. UEs access their subscribed PLMN services and/or subscribed services, including Hosted Services, provided by their participating operators, when entering the Shared NG-RAN.

Network architecture and functionality

3GPP TS 23.501 specifies a network sharing architecture to allow multiple participating operators to share resources of a single shared network according to agreed allocation schemes. The 5G System may support Indirect Network Sharing deployment between the hosting operator (i.e. shared network operator) and participating operator, in which the RAN is shared.

The communication between the shared RAN and the core network of the participating operator is routed through the core network of the hosting operator that connects to the shared RAN. The architecture is illustrated in figure 3:

NOTE: The architecture of Indirect Network Sharing is based on the basic principle of home routed roaming architecture as specified in clause 4.2.4 of TS 23.501. Not all interfaces between the hosting operator and the participating operator are depicted in the Figure for simplicity.

Enhancements for the Indirect Network Sharing aspect:

• New definition and architecture of Indirect Network Sharing in 3GPP TS 22.261 and TS 23.501 accompanied by signaling/procedures updates in 3GPP TS 23.502, and
• NF discovery in the inter PLMN case considering the UE location information, and
• Network slice handling considering the different PLMN IDs broadcast by shared RAN.

Deployment Progress

On May 17th 2024, the World Telecommunication and Information Society Day, China Unicom, China Telecom, China Mobile, and China Radio and Television jointly announced commercial deployment of 5G cross-network roaming technology, as the successful implementation of Indirect Network Sharing as per the 5G-Advanced 3GPP specifications, validating the commercial feasibility of 5G-Advanced network sharing and its compatibility with traditional terminals.

Indirect Network Sharing on Satellite Access Network

Based on Indirect Network Sharing, specified in Rel-19 NetShare items, including; the aspects for the definition, mobility management, network access control and charging… more scenarios and cases can be implemented using INS technology, including satellite use.

One of the challenges for satellite sharing is related with the compatibility and maintenance generated by the interconnection between the network element of sharing parties, e.g., shared satellite access network and two or more core networks of terrestrial participating operators via MOCN.

With Indirect Network Sharing, the satellite access network can be shared by the participating terrestrial network operator without direct interface between the shared satellite access network and participating terrestrial operator’s core network (see figure 4). As LEO satellites are not stationary - with respect to the ground, the limited potential impact in terms of network access control involving both terrestrial and non-terrestrial network needs to be considered.

Indirect Network Sharing - Disaster Conditions

Network sharing may also be applicable in a disaster situation, based on the Rel-19 INS, which requires the pre-configuration of the network. Meanwhile, there is an existing use case in TS 22.261 (clause 6.31) that discusses minimising service interruption associated with roaming during a disaster scenario. However, this method of disaster roaming may not be applicable in some cases due to the potential impact on the UE.

When disaster conditions arise in the specific area, the participating operator’s network (access network, core network, both) may be inoperative. In that case the UE of the participating operator can use the subscribed services via the shared network using Indirect Network Sharing (see figure 5). At that time, issues need to be considered, for example when and how to trigger the NG-RAN of hosting operator to provide the participating operator’s information, and how to select the core network of the participating operator if its core network has failed in the disaster affected area.

Summary

INS defines a new sharing method, with improvements in network access control, registration management, and session management, while the reuse of existing technologies also ensures minimal impact on pre Rel-19 UE, making INS applicable to a wider range of terminals on the market and a variety of business models.

Operators are increasing 5G Network Co-Construction and Sharing and continuously expanding the breadth and depth of 5G coverage. Through 5G Network Sharing, operators make annual savings and are reducing greenhouse gas emissions by millions of tons per year. Network sharing is also providing users with ubiquitous connectivity and high-quality services.