China Telecom's WDM Backbone Network: the Road to All-Optical Network 2.0

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Introduction

In the past ten years, the traffic volume on China Telecom's backbone networks has been growing at an astonishing rate of 47% per year. This poses a range of challenges to equipment investment, equipment room construction, power consumption and loading, and system operations. In an attempt to address some of these challenges, China Telecom is shifting from All-Optical Network 1.0 to All-Optical Network 2.0. The company plans to build a brand new network in line with its CTNet 2025 strategy through interconnection at the optical layer. The new network would be based on an "integrated, concise, agile and open" architecture and lay a solid foundation for future services such as 5G and cloud services.

Project Introduction

China Telecom had good reasoning behind choosing the middle and lower region of the Yangtze River to pilot its All-Optical Network 2.0 project. The region holds 25% of China's population and 30% of its GDP. It boasts a vibrant and innovative economy with a fast-growing data center industry. The region is also home to some of the world's most prominent Internet companies, those of which produce countless new Internet applications every year.

Solution

In 2017, China Telecom built a massive WDM ASON backbone network at 21 nodes throughout Jiangsu, Zhejiang, Shanghai, Hubei, Anhui and Jiangxi. 348 100G WDM links were planned in the preliminary stage, which will eventually be able to support 200G/400G in the future. Through full-mesh networking, China Telecom deployed the first All-Optical Network 2.0 backbone network in China. It differs from the previous All-Optical Network 1.0 in the following aspects:

1.From independent, separate chain topology to full-mesh networking.

The full-mesh network topology creates the shortest service, protection, and recovery routes, allowing for one-hop transmission for services and E2E latency lower than 15 ms to meet CTNet2025 latency requirements. Furthermore, network security was greatly enhanced and fault recovery time significantly shortened.

2.From electric switching nodes to all-optical switching nodes.

21 ROADMs were deployed to create intelligent optical nodes, which will eventually become the optical cross-connect (OXC). This cut construction costs, power consumption, and equipment room sizes of network nodes by 30%—50%.

3.From manual to smart operations.

Full-mesh networks provide the interconnection basis for intelligent operations. Intelligent resource scheduling and on-demand bandwidth and latency can be realized via dynamic path selection at the optical layer and TSDN-oriented networks.

In reference to the new initiative, Wei Leping, Deputy Director of the Science and Technology Committee of the Ministry of Industry and Information Technology, and Director of the Science and Technology Committee of China Telecom, stated, "The dynamic interconnection of the first ROADM backbone network in China initializes the strategic upgrade from electrical nodes to all-optical nodes and from point-to-point links to optical-layer mesh networking. This not only breaks the electrical bottlenecks of network node capacities, but also symbolizes the transition from All-Optical Network 1.0 to the new era of All-Optical Network 2.0. This is also a key step in the evolution towards China Telecom's integrated, concise, agile and open CTNet2025 network reconstruction mission. It not only brings transformation at all layers of the transport network, but also promotes prosperity in related industries."