As the base of the intelligent society, the all optical network has received great attention from the industry and the entire society, and has been placed high hopes, especially in the context of the acceleration of new infrastructure. Leping Wei, Executive Deputy Director of the Communications Science and Technology Committee of the Ministry of Industry and Information Technology and Director of the China Telecom Science and Technology Committee, shared his thoughts on the development trend, evolutionary ideas and required capabilities of all optical network on the "Smart Optical Network 2020 online Forum"recently.
All optical is the trend
Capacity is the biggest driving force for the network towards all optical. The demand for capacity is endless. Leping Wei analyzed that on the demand side, Moore's Law has entered the parallel era, and microprocessors have evolved from single-core to multi-core to Tera-level computing with hundreds of cores. Video has become the major traffic, and video traffic is close to two-thirds of the backbone network traffic. The rise of 4K/8K ultra-high-definition, VR/AR and other big videos intensifies the demand for bandwidth. Other potential demands are emerging, including cloud computing, big data, autonomous driving, etc.. once the scale is formed, higher bandwidth requirements will be imposed.
On the supply side, it evolves from the world’s first 45Mbps backbone optical transmission system official use in the Northeast Corridor of the United States in 1977, to the 48-wavelength 400Gbps system trial commercial use in 2020, and the optical communication capacity has increased by about 420,000 times in 43 years with the annual growth rate 35%. At the same time, the nodes cross-connection particles tend towards the optic. China began to introduce 64K narrowband cross-connection in 1981, and then gradually developed to 2M. In the late 1980s, 140/155M broadband cross-connection was introduced. In 2010, 100G wavelength-level ultra-broadband cross-connection appeared. The service bandwidth between network nodes has transformed from 64K voice to various interfaces of leased line, Ethernet and routers such as POS/GE/10GE/100G. In the past 40 years, the bandwidth particle has increased by about 1.5 million times, which is equivalent to an annual growth rate of 42%. “With the substantial increase in service bandwidth particles, China Telecom’s largest transmission node capacity will exceed 300T in 2020, and will exceed 600T by 2023. The economy and power consumption of the electrical-based multi-chassis combination are difficult to support, and replacing electrical nodes with all optical ROADM/OXC nodes is a reasonable long-term solution.” Leping Wei said. In addition to capacity, latency is also an important advantage of all optical networks. The demand for low latency can only rely on optical network. From the perspective of the OSI 7-layer protocol, the lower the level, the smaller the latency. NE latency on L0 is ns level, on L1 is us level, and on L2/L3 is ms level. By 2025, more than 90% of China Telecom's backbone network will reach 30ms inter-regional latency.
The evolution of all optical network
So how will the all optical network evolve in the future? In terms of capacity, Leping Wei said that from the perspective of the capacity limitation of the switching matrix, assuming 96*100G C-band, a 4-dimensional node can support 4×96 or 384G, and the total bidirectional capacity is 100×384×2 or 76.8T. From the perspective of the CDC capacity limitation of the distributed OXC, the capacity of the optical backplane is basically unlimited, and the number of connected fibers in the line direction and tributary direction can reach 1000 and 2000 respectively. Assuming 96*100G or 9.6T in 1 dimension of WSS，that means 192T for 20 D, 300T for 32 D, 600T for 60 D. For node capacity, add & drop capability of CDC will be the main constraint. 32 D 300T was achieved in 2019, 64 D 600T will come out in 2023. “The existing technology can meet the node capacity requirements for at least three years, after that it is still uncertain. There is no clear solution for how the technology will evolve over 600T in the future. We hope that our development units will work hard.” Leping Wei said. In terms of recovery time, he pointed out that the current recovery time of the all optical network takes a few minutes, and hopes to drop to 10+ seconds or even less than 10 seconds. First, we must implement service classification based on service value to ensure the recovery time of high-value services, and even the protection routing link table can be issued in advance. Second, the centralized path calculation and distributed control architecture, by introducing the centralized path calculation PCE, we can effectively avoid rerouting wavelength conflicts and reduce recovery time. Third, the introduction of SDN is expected to make the best use of the bandwidth resources of the entire network, shorten the convergence speed, and reduce latency. SDN can also obtain the service path with the shortest latency according to the reporting link. Finally, machine learning is introduced to realize the prediction of optical performance degradation, fiber or equipment failure, and save service commissioning and recovery time and even active rerouting. Take the case of AT&T, based on the ASON network, it achieves availability of 99.9999%, reduces CAPEX by about 50%, reduces OPEX by about 60%, 99% of priority services can be restored within 1 second, and 99% of basic services can be restored in 10 seconds. “The key to ROADM's further expansion to the edge of the network is cost, and the key to reducing costs is technological innovation and economies of scale.” Leping Wei advocated. At the physical layer, removing unnecessary functions and unnecessary temperature requirements at the edge of the network, relaxing optical device requirements, eliminating heaters and refrigerators, etc., is expected to greatly reduce the cost and power consumption of core optical devices. At the network layer, with SDN-controlled, software and hardware decoupling "gray box" or even "white box", open and standardized interface and interoperability of data planes, we can promote the open ecology of optical networks. Finally, in order to obtain the huge economic scale benefits of global cellular and reduce fragmented private specifications, it is necessary to set a F5G with a unified definition, architecture, functions, capacity, and performance. All optical network needs SDN control to have cross-network, cross-technology, and cross-vendor vision of the entire network. He said that in addition to making the best use of the bandwidth resources of the entire network, shortening the convergence speed and realizing the best routing, the most important thing is that it is conducive to breaking through the barriers of cross-network, cross-technology, cross-vendor, and is conducive to cross-layer integration. “ROADM does not solve the inter-layer control and coordination mechanism, and the cross-layer vision of SDN is expected to solve it.” Leping Wei said. The all-optical network also needs to be programmable, aiming to realize minute-level settings of rate, modulation format and wavelength interval. This requires the programming of WDM system boards, wavelength selection switch, optical devices, etc. All optical network must also move toward an open ecosystem. In order to cope with the increasingly severe situation of weak industry development and increasing external competition pressure, reducing costs and creating a healthier and more active industrial ecosystem have become the key to sustainable development. Starting from the wireless access network, all areas of the network will gradually open up, with interface standardization, software and hardware decoupling, hardware white boxization, and software cloudification, the all optical network will be no exception. At last, the all optical network needs artificial intelligence to empower. AI can be applied in all fields of the all optical network, bringing great driving force. At the end of the speech, Leping Wei also introduced the progress of China Telecom's all optical backbone network 2.0. At present, this network includes five regions, with a total system length of 220,000 kilometers, radiating 470 ROADM nodes, 2357 OA nodes, and a total network capacity of 590T.
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