fgOTN to revolutionise communication networking in the power sector

Huawei has launched the first fgOTN-compliant optical transmission product for the power sector and other industrial applications.

Over the past few decades, SDH (Synchronous Digital Hierarchy) technology, which features high reliability and deterministic low latency, has been widely used in private networks in industries such as electric power and transportation and in those of carriers, governments and enterprises.

As intelligent services continue to grow, SDH technology has had to confront its bandwidth challenge. Currently, it only supports a maximum of 10Gbps bandwidth. In addition, legacy SDH devices on the live network are gradually being removed. Therefore, a new technology is urgently required to support the services carried over legacy SDH networks.

In December 2023, the ITU Telecommunication Standardisation Sector (ITU-T) officially approved the fgOTN (fine-grain Optical Transport Network) standard and defined it as the next-generation technology for SDH evolution.

Dr. Xiang Liu, a senior expert in international optical communications standards, explains: “In addition to SDH, fgOTN is the only technology standardised internationally that supports constant bit rate (CBR) services in the industry, as well as efficiently supporting Ethernet services with agile hitless bandwidth adjustment. The release of the fgOTN standard signifies the transition of communication networks from the SDH era to the fgOTN era.”

Why we need fgOTN standards

The OTN technology features long distance, large capacity, physical isolation, low latency, low jitter and low power consumption per bit, therefore, is suitable for use in long-haul backbone scenarios.

Small granularity services with a bandwidth lower than 1Gbps remain the mainstream on industry private networks and lines. Examples include relay protection for electric power and railway train control services.

However, the minimum service granularity supported by OTN is 1.25Gbps. Thus, when small granularity services are implemented, bandwidth is wasted, and services carried over SDH networks cannot be migrated to OTN networks. Small granularity OTN technology is urgently needed to provide isolated, highly secure and highly reliable transmission, smoothly carrying SDH services on the live network.

In addition, SDH technology is based on the ITU-T G.707 standard, and OTN technology is based on the ITU-T G.709 standard, a later version of the G.707 standard. The introduction of fine-grained bearer technology under OTN standards will help address the SDH network evolution challenge that the industry is facing.

Against this backdrop, in 2020 ITU-T initiated a research project on carrying services lower than 1Gbps on OTN networks. Based on existing OTN standards (the G.709 series), ITU-T defined new fgOTN standards to support the small granularity hard pipe technology that will replace existing SDH technologies to carry small granularity services such as power relay protection.

As such, it is better able to meet the new service requirements of private lines and production networks. Moreover, the fgOTN standards are compatible with existing OTN networks, meaning that customers’ investments in existing OTN devices are protected and that network upgrades will go through smoothly.

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Technical features of fgOTN standards

fgOTN is a small granularity hard pipe technology based on the OTN standards system. It is mainly used to carry premium services lower than 1Gbps and can be widely used in the private lines of carriers, governments and enterprises as well as on private networks in industries such as electric power and transportation.

fgOTN inherits the advantages of OTN and SDH in TDM (Time-Division Multiplexing) technology. It adopts the fixed timeslot allocation design (unit: 10Mbps bandwidth), inherits and optimises the typical OTN frame structure to efficiently carry small granularity services, and supports multiple variable and constant bitrate (VBR, CBR) services such as ETH, E1, and SDH. All this provides a highly secure physical isolation solution using hard pipe technology and delivers high-quality connections.

fgOTN has undergone seven technological upgrades:

1. Physical isolation: Fixed 10Mbps-based timeslot division provides strict physical isolation and hard pipe transmission capabilities.
2. Low latency and jitter: Fixed 16 b timeslot interleaving ensures microsecond-level latency and low jitter.
3. Simplified fgGMP mapping: The asynchronous mapping from fgODUflex signals to service-layer OPU signals is simplified to reduce latency and mapping overheads.
4. High-performance clock transparent transmission: The innovative clock phase hop-by-hop accumulation technology is used to provide high-performance clock transparent transmission for CBR services. Services are centrally processed at the end node, lowering the processing costs of traditional OTN hop-by-hop clock recovery solutions in cases where there are numerous services.
5. Efficient bearing: p*10Mbps fgODUflex flexible containers provide efficient bearing of multiple services (ETH/E1/SDH).
6. Optimised fgODUflex frame design:
   • Innovative fast framing: Frame alignment signals (FAS0–FAS7) are transmitted in multiple rows and columns in sequence, achieving fast framing.
   • Highly reliable monitoring: fgODUflex optimises and innovates OAM (six-layer TCM simplified to two-layer TCM), which can monitor subpaths at a low cost and meet the requirements of carrying small granularity services.
   • Accurate latency measurement: The optimised latency measurement mechanism implements high-precision latency measurement within nanoseconds.
7. Fast hitless bandwidth adjustment: Only one step is required for hitless bandwidth adjustment, which can be completed within hundreds of ms.

Industry’s first fgOTN-compliant optical transmission product

Huawei unveiled a groundbreaking optical transmission product at the World Mobile Congress 2024 (MWC 2024), marking the industry’s first introduction of a product supporting the fgOTN standard.

This innovation establishes a robust and reliable communication network for the electric power and transportation sectors.

During the Global Optical Summit（GOS）APAC 2024, Huawei released the fgOTN Technical White Paper. The White Paper provides a detailed description of the fgOTN standard series, key technologies and application scenarios, proposes the industry target network architecture based on the fgOTN standards and describes the prospect of future optical communication applications in a range of industries.

fgOTN, developed based on the SDH technology, is the best choice for SDH network evolution in terms of standards, technologies and industries. fgOTN technology can seamlessly replace existing SDH technology and is compatible with the existing OTN network, effectively protecting the investment on existing OTN devices.

The application of fgOTN technology in vertical industries such as electric power and transportation and carrier networks will not only further accelerate commercialisation. Still, it will also promote the entire industry chain’s healthy, continuous and stable development.

View more information about fgOTN here.