Analysis on 5G-R Transport Technology

Background

China State Railway Group issued the “National Railway Planning Outline for Transportation Powerhouse in New Era” in 2020, outlining the direction for advancing railway communication technologies. The outline emphasizes tasks such as developing independent and advanced technological equipment systems, improving the technological level of infrastructure equipment, and empowering smart development through new infrastructure.

To implement China’s decisions on deploying 5G networks and other new infrastructure, the Group has set the goal of building a dedicated 5G mobile communication system for railway (5G-R). This large-scale 5G private network will support railway production and operations. As IP-based railway services grow, objectives for intelligent network operation, resource management, system maintenance, and service applications become clearer. New requirements have been raised for the next-generation railway transport network technology, including secure and reliable 5G-R communication for transportation-related production services, 5G-R slice isolation, transport of multiple existing services, and manageable railway private networks.

To enhance 5G-R construction, the primary focus of the current transport network is selecting a suitable transport solution based on 5G-R’s key requirements and the development evaluation of railway multi-service transport. In the 2022 5G-R transport solution research project led by China Railway Signal & Communication Corp Ltd (CRSC), the IMT-2020 5G transport promotion group thoroughly analyzed SPN, IPRAN, and M-OTN solutions. The current SPN, based on new international standardized technical solutions with deep integration of TDM and packet technologies, holds relative advantages and is expected to become the primary choice for 5G-R access backhaul and integrated railway transport.

SPN 1.0 has been widely adopted by operators and is evolving to 2.0 for multi-service transport. Featuring fine-granularity 10M FGU hard-isolation slicing with 10GE interfaces, E1/STM-1 CBR multi-service transports, mature coarse-granularity MTN hard-isolation slicing, high-precision inband OAM performance measurement, and manageable transport, it can transport 5G-R and traditional railway communications services from L1 to L3, while ensuring high-isolation, high-reliability, and manageable transport of existing SDH services.

Major Challenges

Operators have put 5G into large-scale commercial use. 5G-R, as the private network technology for railways, faces differentiated demands for railway production and operation. The primary challenges include:

• L3 networking with transport features: 5G-R inherits the transport network features of GSM-R and introduces flexible L3 networking in addition to bandwidth requirements of the existing SDH/MSTP transport network. It maintains SDH/MSTP hard isolation, high reliability, manageability and controllability, along with other transport features like L3 bidirectional connection, comprehensive traffic planning, complete OAM and protection, addressing the quality needs of the railway private network.
• Secure isolation and reliable transport: The 5G-R system needs to support railway production services such as dispatch communication and train control. Moreover, it involves operational support services such as video monitoring, line inspection, and other railway applications, all requiring secure and reliable transport equivalent to or even higher than traditional SDH/MSTP. TDM hard isolation is provided between production operations, operational support services, and other applications.
• Large-scale private network management and control: The nationwide large-scale 5G-R private network has higher requirements for network planning, construction, maintenance, and optimization. All network services are manageable and controllable, with enhanced management and control capabilities of the transport NM facilitating fast service deployment, stable operation, easy troubleshooting, and intelligent O&M. Therefore, using the integrated management and control architecture to inherit and continually evolve the management and control capabilities of existing SDH/MSTP is reasonable.

Technology Analysis

During the 5G network design phase, the white paper “5G Transport Network Architecture and Technology Solution” released by the IMT-2020 5G transport promotion group in 2018, evaluates three 5G transport technologies (SPN, IPRAN 2.0, and M-OTN) and analyzes three transport solutions. These solutions reflect the ongoing convergence and advancement of transport and packet technologies, differing in the layer and depth of transport and packet convergence. Figure 1 outlines the development of the transport technology route.

These three transport technologies vary in their support for 5G-R transport.

• M-OTN still employs dedicated OTN interfaces and offers TDM hard isolation slicing, but lacks 5G backhaul applications and L3 networking.
• IPRAN 2.0 supports L3 networking but lacks sufficient enhanced capabilities in the transport network, including TDM hard isolation and various manageable and controllable features.
• SPN boasts both TDM hard isolation and L3 networking capabilities. It has carried 5G services on a large scale, offering rich manageable and controllable features.

Operators have also carried out performance comparison tests for three transport technologies in addition to technology analysis. The test data analysis shows that SPN leads in key performance indexes that support 5G and integrated service transport (Fig. 2).

The IMT-2020 5G Transport Promotion Group’s research report on 5G-R transport solutions shows that among the three options, SPN has superior technical satisfaction. In the recent 5G-R technical selection test, ZTE’s SPN successfully completed all test requirements.

The ITU-T has released international standards for SPN 1.0 and completed the establishment of formulation of G.fgMTN standards for SPN 2.0 FGU. Over 400,000 SPN devices are deployed in existing networks and are increasingly used in production private networks like power, subway, high-speed rail, and mining. Mature 5G-R transport industry chains are now available.

Considering the primary challenges outlined for 5G-R transport network and the current development roadmap of transport network technologies, adopting an SPN-based 5G-R solution offers the following advantages:

• Building an end-to-end 5G-R backhaul L3 network with SPN, enabling soft/hard-isolation slicing for 5G services, and achieving manageable and controllable private network services.
• Supporting E1/STM-1 CBR transport through SPN TDM hard isolation channels,  enabling the comprehensive transmission of both 5G-R and railway production services.
• Utilizing SPN’s standard independence and industry chain advantages to construct a next-generation integrated service access and transport platform for railways, supporting the overall strategy of becoming a 5G-R transportation powerhouse.

From the perspective of overall 5G-R construction objectives, SPN 2.0 technical standards and products align well with its transport construction requirements, offering advantages in technical capabilities. Currently, China State Railway Group is conducting a range of 5G-R verification tests, with ZTE SPN actively cooperating. ZTE has prioritized meeting the 5G-R transport requirements with SPN 2.0 in product planning and R&D, contributing to the development of smart railways.