400G Optical Transmission Sets Sail in China
In 2009, Verizon deployed the first commercial 100G optical link between Paris and Frankfurt. Subsequently, the 100G signal modulation scheme and coherent reception technology proposed by Alcatel-Lucent were incorporated into international standards, greatly accelerating the industrialization of this technology. In 2013, 100G technology experienced explosive growth in the global market, with 100G revenue approaching 15% of the overall market. In the Chinese market, the scale of 100G centralized procurement by China Mobile and China Telecom continued to break world records. Therefore, 2013 was also called the "first year of commercial deployment in China" for 100G technology, and the industry widely believed that 100G technology had opened a "golden decade" of commercial application. Amid this surging 100G wave, in early 2014, Alcatel-Lucent's flagship company in China, Shanghai Bell, announced the successful completion of China's first 400G optical transmission test based on a commercial platform, in cooperation with the China Mobile Research Institute. Compared with the transition from 10G/40G to 100G, the fact that the country's largest mobile operator shifted its attention from 100G to 400G in such a short time quickly turned the industry's focus toward 400G and even higher-speed optical transmission technologies.
400G optical transmission technology is no longer unfamiliar to the industry.
In early 2012, Alcatel-Lucent was the first to release a commercial 400G PSE chip, followed by Ciena, which also released a 400G commercial chip.
At OFC 2013, Ovum analysts believed that the deployment of 200G-400G would come faster than expected, especially in high-traffic areas where this trend would be even more pronounced. 400G had already demonstrated its value in high-bandwidth application scenarios such as data center interconnection.
In the same year, Alcatel-Lucent's 400G commercial platform took the lead in commercial deployment globally and was installed on the live networks of several major operators in Europe, North America, and Asia-Pacific. All of this made it seem that the pace of 400G commercialization was perhaps too fast.
400G optical transmission technology will become a key technology in the post-100G era.
From an industry perspective, whether for operators or mainstream global equipment vendors, mastering leading 400G technology means mastering the future direction of network development. Therefore, 400G technology will become the high ground that operators and equipment vendors will compete for in the future.
At the "2013 Mobile Internet International Symposium," experts from the China Mobile Research Institute stated that in terms of beyond-100G technology, China Mobile would take the initiative, tackle core technologies, actively explore the development direction of post-100G technologies, and continuously enhance the fundamental bearing capacity of networks. Currently, 400G standardization efforts are progressing in various standards organizations, and major transmission equipment vendors are already able to provide 400G transmission equipment. China Mobile will conduct 400G testing in 2014.
At the "2013 Optical Communication Technology and Development Forum," Wei Leping, Director of the Science and Technology Committee of China Telecom, pointed out that according to current traffic growth trends, over the next five years, network traffic would grow by nearly 40% annually, dominated by 100G. By 2017, the maximum cross-section transmission bandwidth of the backbone network would be approximately 38Tb/s, requiring five 80-wavelength 100G systems. As long as it is feasible, 400G would be a more reasonable choice. Over the next 5-10 years, network traffic would grow by about 30% annually, and high-traffic areas would require 45-125Tb/s. As long as it is feasible, 400G should be the dominant rate.
400G optical transmission technology currently still faces standards disputes.
In the 40G era, due to the lack of unified technical standards, the coexistence of multiple technical formats led to poor interoperability, high costs, and slow commercialization. 100G technology also experienced standards disputes before standardization, and ultimately the PDM-QPSK modulation scheme and coherent reception technology advocated by Alcatel-Lucent unified the standard with excellent performance. Similarly, for beyond-100G standards, standards disputes are inevitable. Whether chip vendors or system integrators, the current focus is mainly on 400G. As the lesson of 40G shows, without unified standards, 400G may repeat the mistakes of 40G. Currently, the 400G systems of major vendors adopt the following three implementation approaches:
* Building a 400G super channel using four-carrier 100G PDM-QPSK
The advantages of this approach are: 100G technology has been commercially deployed at scale, with mature technology, low cost, and long reach.
* Building a 400G super channel using dual-carrier 200G PDM-16QAM
The advantages of this approach are: spectral efficiency is improved by more than 165%, with higher system integration, smaller size, and lower power consumption. It has already begun commercial deployment.
* Building a 400G channel using single-carrier 400G PDM-32QAM
The advantages of this approach are: spectral efficiency is improved by more than 300%, with high system integration.
Among the three approaches above, the single-carrier approach offers the highest spectral efficiency and appears to be the best solution. However, due to the limitations of Shannon's law, it is extremely difficult to implement, has high costs, and short reach (<200Km). Without major technological breakthroughs, its prospects for long-haul transmission applications are not optimistic.
Industry experts have pointed out that with the current level of technology, the single-carrier approach is only suitable for metro applications. The four-carrier approach has the advantages of mature technology, low cost, and long reach, but it is only meaningful if spectral compression technology is introduced to improve spectral efficiency and chip upgrades solve integration and power consumption issues. Otherwise, a 400G system built with current 100G chips is essentially still a 100G system. As for the dual-carrier approach, its greatest advantages are high spectral efficiency and the fact that it has already begun market commercialization. Vendors represented by Alcatel-Lucent and Ciena can already provide 400G commercial chips, which may directly influence the direction of the 400G standard. However, given the quality of fiber and optical amplifiers currently deployed at scale in China, the reach of this approach is relatively short, with commercial reach of around 500km, which imposes certain limitations in long-haul transmission scenarios. If combined with low-loss fiber and new optical amplifiers, the reach of the dual-carrier approach can exceed 1000km, basically meeting long-haul transmission requirements. The "Eight Vertical and Eight Horizontal" backbone network laid in the 1990s is now approaching retirement, and China Telecom has taken the lead in adopting low-loss fiber in the new round of fiber network construction. Typically, these newly laid fibers have a 20-year lifecycle, laying a solid foundation for the commercial deployment of 400G, 1T, and even higher-capacity optical communication systems.
The technical threshold for 400G optical transmission is very high.
The essence of transmission is to deliver information over long distances with higher spectral efficiency and lower cost. In the beyond-100G era, further increasing system capacity and performance will face enormous challenges. Therefore, finding a balance between efficiency and cost will influence the development of the 400G standard. As can be seen from the relationship between the Shannon curve and modulation schemes, further increasing spectral efficiency means higher signal-to-noise ratio requirements, which will directly lead to significantly greater technical implementation difficulty and rapidly rising costs for 400G systems.
As can be seen from the standards disputes mentioned earlier, the choice of 400G technology direction is essentially a contest of vendors' technical strength. As the core technology of ultra-high-speed optical transmission, the development difficulty of ultra-high-speed digital signal processing chips has greatly increased since the 100G era. As a result, even to this day, very few equipment vendors truly master this technology. Bell Labs successfully demonstrated 100G as early as 2005, but it was not until 2010 that it began providing 100G DSP chips. The technical difficulty is evident from the length of the R&D cycle. In 400G technology, the implementation of ultra-high-speed optoelectronic digital signal processing and chips remains the greatest challenge. Since ultra-high-speed optoelectronic processing and related chips involve fundamental fields such as optics and microelectronics, 400G requires substantial technical accumulation and process innovation in spectral efficiency, transmission distance, integration, cost, and power consumption to meet commercial requirements. This is the biggest obstacle most equipment vendors face in developing 400G technology.
400G optical transmission systems involve the following key technologies, such as:
High-order modulation schemes that improve spectral efficiency;
Suppression and compensation technologies for fiber nonlinear effects;
More efficient and higher-gain forward error correction (FEC) coding;
Digital signal processing with more efficient algorithms and larger-scale processing capabilities;
Higher-speed analog-to-digital conversion (ADC) technology;
Flexible grid technology that can adapt to multiple spectral widths (Flex-grid)
Only by fully mastering all of the above technologies can a truly future-proof 400G commercial system be provided. Thanks to the strong R&D capabilities of Bell Labs, the 400G PSE released by Alcatel-Lucent from 2012 to the present remains globally leading, representing the highest level of commercial ultra-high-speed transmission in the industry. Clearly, through this cooperation with the China Mobile Research Institute, Alcatel-Lucent has once again demonstrated its strong strength in the 400G field, both in core chip technology and system integration capabilities.
As equipment vendors in the midstream of the industry chain, whether they master core ultra-high-speed 400G technology will directly affect their long-term product planning, which in turn will indirectly affect the overall network construction costs and telecommunications tariffs. Having long stood at the forefront of optical transmission and possessing excellent technological foresight, Alcatel-Lucent's 400G solution is based on a product platform that has been in global volume supply since 2008. This product platform was built on a high starting point from the very beginning of R&D, enabling optical transmission networks built on this platform to smoothly evolve from 10G to 400G. Such a long-span product evolution roadmap is extremely rare in the optical transmission field. The benefit of this smooth evolution is that operators' networks can quickly upgrade from 10G to 100G or even 400G with virtually no changes to the network. On the one hand, operator investments are greatly protected and saved, and network services remain stable. On the other hand, users can enjoy a better service experience while indirectly benefiting from lower telecommunications tariffs.
As the first equipment vendor to participate in the test, this demonstrates China Mobile's recognition of Alcatel-Lucent's technology and strength in the ultra-high-speed transmission field. It is believed that Alcatel-Lucent's 400G system will help operators further increase network bandwidth in the near future, bringing users a better service experience in the Internet era.
Source: C114 China Communication Network