You talk about 5G every day. Do you know about the new generation of optical transmission network technology?

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5G is the hottest word in the communications industry and even in the whole society. We talk about 5G every day, but do you know the blood vessel system of 5G network - optical transport network?

The 5G era of the Internet of Everything will generate a massive amount of data. Except for the last few hundred meters of wireless transmission through 5G base stations, the rest of this data has to be carried by a huge optical network. If data is likened to "blood", the optical network is the "vascular system" of 5G. In the 5G era, network data traffic has increased exponentially. How will this "vascular system" efficiently transmit the "blood"?

Now, let's go to the 2019 Annual Conference of the Next Generation Optical Transport Development Forum (NGOF) held in Shenzhen on January 8, 2020, and see how NGOF promotes the efficient operation of this "vascular system"?

From "capillaries" to "arteries", NGOF promotes the innovation of next-generation all-optical network technology

As we enter the 5G era, the exponential growth of data traffic has had a far-reaching impact on the network. For optical networks, the entire "vascular system", from edge access to metropolitan areas and backbones, from "capillaries" to "arteries", requires a technological upgrade.

Let's talk about "capillaries" first. As we all know, the bandwidth of the fronthaul interface (CPRI) between the BBU and RRU of a 4G base station is only 9.8Gb/s, while the bandwidth of the fronthaul interface (eCPRI) between the 5G DU and AAU will be increased several times. For a 5G single macro station, three 25Gb/s eCPRI interfaces are required under a 100MHz spectrum bandwidth. If China Telecom and China Unicom are considered to build and share together, a 200MHz spectrum bandwidth requires six 25Gb/s eCPRI interfaces.

Considering that the 5G era will adopt a DU-centralized C-RAN architecture, DU connects multiple distributed AAUs through the fronthaul network. This means that if the traditional deployment method is followed, the 5G fronthaul network will require a large amount of optical fiber, which poses new challenges to deployment costs, operation and maintenance management, etc.

To this end, as an industry organization dedicated to collaborative innovation in optical transport networks, NGOF established a research group for 5G fronthaul technology as early as the end of 2017. It proposed a 25Gb/s single-fiber bidirectional (BiDi) technology solution for C-RAN scenarios and a metropolitan access DWDM (formerly G.metro) technology solution for 5G large-scale concentration and integrated business carrying. It also worked with member units to quickly complete standardization and promote the maturity of the industry chain.

The NGOF annual conference also released the "5G Fronthaul Technology and Application White Paper", which analyzed the 5G fronthaul requirements, compared and analyzed the current various wavelength division-based fronthaul technology solutions, proposed fronthaul network construction and operation and maintenance methods, and pointed out that the selection and application of 5G fronthaul technology solutions should follow the principles of fixed-mobile convergence, integrated bearer, resource guarantee, moderate advancement, quality assurance, cost priority, unified management and control, and clear interface.

In response to the new demand for doubling the fronthaul bandwidth of a single base station brought about by co-construction and sharing, NGOF will continue to study low-cost WDM technology solutions that support 12 or even more wavelengths, further promote the maturity and perfection of the industry chain based on 25Gb/s tunable optical modules, and collaborate with operators, optical module manufacturers, transmission bearer equipment manufacturers, and wireless equipment manufacturers to jointly solve the management and maintenance problems faced in 5G fronthaul solutions.

Let's talk about "arteries". With the continuous and rapid growth of network traffic, the single-fiber capacity needs to continue to increase. According to the current development trend, the DWDM system widely used in backbone networks and metropolitan area networks needs to evolve from single-wavelength 100G to single-wavelength 200G and 400G.

The main paths to achieve higher single-wavelength rates are: higher-order modulation formats, higher baud rates, and more subcarriers. However, if a higher-order modulation format than single-wavelength 200G is used to achieve single-wavelength 400G, its transmission capacity will inevitably decrease; but if single-wavelength 400G is expected to maintain the transmission capacity of single-wavelength 200G, a higher baud rate or more subcarriers is required to achieve this. Neither of these two paths significantly improves spectral efficiency.

Therefore, to increase the single-fiber capacity to the single-wavelength 400G era, the DWDM system needs to increase the available spectrum bandwidth and expand the C-band.

To this end, NGOF released the "Extended C-band WDM System Technology White Paper", which studied the extended C-band system from the aspects of optical spectrum bandwidth, performance, optical layer, industry chain maturity, unit bit cost, operation and maintenance, etc., and analyzed the maturity of key components used in the extended C-band. It plans to launch standardization work in 2020, promote pilot applications, and strive to achieve commercial deployment in 2021.

In addition, in response to the trend of large-capacity DWDM technology sinking from the backbone network to edge access, NGOF established a new working group at this conference - the Tunable Laser Special Working Group.

Tunable DWDM lasers have been widely used in backbone networks and metropolitan core aggregation networks, and practice has proven that they can greatly simplify network construction and operation and maintenance. Facing the increasing demand for broadband in the future, how to promote the application of low-cost tunable WDM technology to the metropolitan edge access layer is an urgent problem to be solved by the industry.

In the next step, the Tunable Laser Special Working Group will be guided by the application needs of low-cost tunable WDM technology, focusing on scenarios such as 5G fronthaul and professional access, and based on the ITU-T G.698.4 international standard, formulate relevant technical specifications to guide the industrial chain.

OTN quality private line five-star index system helps operators to grow their B2B business

There is no doubt that as enterprises move to the cloud and 5G empowers all industries, government and enterprise dedicated line services will definitely be the main business growth point for operators in the future and the focus of competition in the 2B market in the 5G era.

To this end, NGOF innovatively proposed a five-star indicator system for quality private lines, defining the evaluation system for high-quality private lines from five dimensions: guaranteed bandwidth, high availability, low latency & low jitter, business agility, and online self-management. It also developed a five-level differentiated SLA indicator system to guide operators and equipment vendors to provide differentiated private line products and services.

Based on this quantitative indicator measurement system, NGOF conducted a comprehensive analysis of various private line bearer technologies and concluded that packet-enhanced OTN is the best bearer technology for high-quality private lines, which can effectively meet the high-quality experience requirements of various high-value government and enterprise customers.

Zhao Wenyu, leader of the NGOF Cloud & Private Line Working Group and director of the Broadband Network Research Department of the Institute of Technology and Standards of the China Academy of Information and Communications Technology, said that at present, operators in more than 20 provinces in China have built OTN private lines, and a large number of operators are in preparation. The relevant capabilities of OTN quality private lines have been fully demonstrated in the practices of various operators, and the quality private line business revenue of the three major operators has also achieved significant growth, which shows the natural advantages of OTN technology in the construction and application of quality private line networks.

In the future, OTN technology will continue to evolve as market demand changes, providing high-quality connection services to thousands of industries with higher resource utilization efficiency and more economical methods. Currently, OTN technology based on OSU for smaller granularity has been successfully established in the China Communications Standards Association (CCSA). The NGOF private line project team will also combine this technology to focus on exploring the possibility of OSU-based OTN in the following more scenarios:

• Smaller and more flexible service forms: Flexible adjustment from Mbit/s to Gbit/s, no longer limited by the traditional ODU0 granularity, can match existing service granularities such as SDH, Ethernet, packet switching, and OTN switching.
• More economical resource utilization: Provide private line-quality services to small and medium-sized enterprises and even individuals, such as flexible small bandwidth, on-demand use, and lossless bandwidth adjustment, while retaining many high-quality features of traditional OTN private lines.
• Lower latency: Simplifies the data exchange mechanism, reduces the number of business layers to be processed, and significantly reduces device latency. It can be applied to latency-sensitive scenarios such as financial systems, autonomous driving, industrial intelligent manufacturing, and large-scale collaborative computing.

Founded only two years ago, NGOF has achieved remarkable results

The above introduces some of the innovative achievements of NGOF in 2019, but NGOF has achieved more than that. NGOF was established in December 2017. The initiators include operators, research institutes, equipment manufacturers, module and device manufacturers, chip manufacturers, optical fiber and cable manufacturers, etc. Its mission is to unite the entire optical transmission network industry chain and fully cooperate in demand analysis, technology innovation research, standard setting, testing and verification, pilot applications and other fields to accelerate the commercialization of the next-generation optical transmission network technology and enhance the global technology and industry leadership of Chinese companies in the optical network industry.

In the past two years, the number of NGOF member units has expanded from 14 at its inception to 40, covering the complete upstream and downstream industrial chain in the field of optical transmission networks; the working groups have expanded from 3 to 6, including the 5G bearer working group, the metropolitan optical module working group, the cloud & dedicated line bearer working group, the submarine cable communication working group, the large-capacity WDM transmission working group, and the newly established tunable laser ad hoc working group.

At the meeting, Li Junjie, director of the NGOF office and chief expert of China Telecom's optical transmission, summarized the main achievements of NGOF in 2019. In the past year, NGOF has made remarkable achievements, released four white papers on high-quality private lines, silicon-based optical devices, 5G fronthaul, and extended C-band transmission, jointly promoted the pilot application of two new technologies in the live network, and coordinated the completion of four ITU-T/CCSA technical standards and research projects, and coordinated the establishment of four ITU-T/CCSA technical standards.

In 2020, NGOF's six working groups will continue to promote or newly launch technical research, standardization work or industry chain maturity in the fields of cloud and cloud-network collaborative service optimization bearer solutions, new OTN technologies, quality private line evaluation systems and intelligent operation and maintenance, metropolitan N×25G/s WDM system technology, low-cost tunable lasers, extended C-band transmission technology, and 5G fronthaul technology.

After decades of continuous development, my country's optical communication industry has been at the forefront of the world, and has even entered a "no man's land" in many fields. There is no leading benchmark reference ahead, and more cooperation and continuous exploration and innovation are needed from the entire optical communication industry chain. I believe that with the promotion of NGOF, my country's optical communication industry will surely create greater glory in the next decade of communications.