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Given its efficient signal conversion and transmission capabilities, optical transmission networks have long been the foundation for Local Area Data Networks (LADNs), wide area switching networks, and backbone networks. Globally, optical transmission technologies predominantly include synchronous Time Division Multiplexing (TDM), synchronous optical channels, and Synchronous Digital Hierarchy (SDH). Other industry technologies — including Plesiochronous Digital Hierarchy (PDH), SDH, Multi-Service Transmission Platform (MSTP), and Optical Transport Network (OTN) — continue to evolve.
In addition to providing basic communication connections for the backbone and networks of many operators, optical transmission technologies are also used in the production communication networks of diverse industries, providing secure, reliable, and efficient communications. Currently, SDH and OTN are widely used physical pipe isolation technologies.
Physical pipe isolation provides guaranteed bandwidth along with low data transmission jitter and low latency; the time division feature fulfills the environmental requirements of time synchronization. Moreover, the utilization of a clock transmission solution ensures simple and reliable network-wide production network communication.
The electric power industry provides useful illustration. A significant number of communication private lines are required for different production services on an electric power production network. These private lines carry numerous low-rate and small-granularity services (the bandwidth of production services is generally less than 100 Mbit/s). The service rate of a single production device typically ranges from 2 Mbit/s to 100 Mbit/s. This requires high communication and response performance including low latency and low jitter. Equally important is the assurance of high-level stability. For example, relay protection services of the power production network require a rate of 2 Mbit/s and a latency of under 10 ms. Traditional power production private lines commonly use TDM SDH/MSTP technology to carry such key production network services.
With the emergence of cloud, virtualization, and digital technologies, many industries — including the electric power industry — have followed a path of transformation, upgrading their production and operation modes as they do so. According to the manufacturing sector's Industry 4.0 strategy, production automation brings high-sensitivity machine interaction, while Internetization in the OTT industry brings growth in data traffic and data center scale. Both the energy industry's legacy and new energy production and operation modes, for ubiquitous connections, generate growing network complexity and data scale. Elsewhere, in the transport sector, high-speed train control and integrated operations boost security, while in the financial industry, digital transactions increase traffic and improve overall efficiency. As each industry differs distinctly, the communication transport network for production and operations of each must satisfy several requirements.
• Rate: The communication connection rate should range from 2 Mbit/s to 100 Gbit/s and not affect the production of enterprises or hinder productivity.
• Cloudification: 96% of enterprises or organizations are already using the cloud. The high rate and bandwidth of optical fiber communication ensures that data and applications stored in the cloud can be accessed more efficiently. As more and more more services are migrated to the cloud, the latency and rate of optical fiber communication technologies will guarantee zero delay interaction.
• Reliability: Any unexpected downtime will completely halt service communication and production, causing enterprises to lose money. For example, a major power network collapsing would cause significant financial damage to the power enterprise and may have significantly adverse effects on the country as a whole. While optical fibers are physically difficult to interfere with, they also have self-healing capabilities.
• Latency: Automatic production, secure operations, and cloud applications all require extremely low latency. Achieving a guaranteed latency brings enormous benefits, improving user service quality and facilitating the migration of applications to the cloud, as well as achieving collaboration for mechanical automation and fast transaction services.
In terms of technology, traditional SDH/MSTP is very resilient and can guarantee bandwidth. Additionally, it can effectively adapt performance for production device services. However, this technology does suffer from bottlenecks, particularly in the scale-up of communication rates and flexibility of network operations. Numerous TDM and Synchronous Optical Network/Synchronous Digital Hierarchy (SONET/SDH) devices currently in use are approaching the end of their lifecycle. Despite displaying inherent advantages in bandwidth evolution, the OTN hard pipe cannot adapt to service rates lower than 1.25 Gbit/s. Compared with SDH, OTN has a more complex encapsulation structure, resulting in higher latency. However, OTN has a relatively fixed bandwidth — the same as SDH — which makes it increasingly difficult to flexibly and efficiently address digitalization requirements. Therefore, in terms of evolution, a next-generation TDM optical communication technology is required to adopt SDH technology and carry high-performance narrowband production network services. Additionally, the technology is required to fulfill the requirements of flexible and visualized large-bandwidth backbone data transmission.
Today, IP MPLS and MPLS-TP solutions are often used to replace the recommended SDH solution. However, in WAN production networks carried by both national backbone and metro networks, it is difficult to provide a suitable time synchronization solution and efficient service reachability. This is due to the uncertain time sequence of IP transmission service packets. Based on IP MPLS and MPLS-TP, vendors have developed technologies similar to the IP or SPN hard pipe time division mechanism. In essence, the mathematical transmission model of the SDH hard pipe time division system is introduced again to the IP framework. However, due to the fact that IP technology architecture is not based on the hard pipe time division system, such improvement relies on proprietary technologies. Therefore, it is difficult for vendors to formulate unified hard pipe and time division technical standards, with standard network interconnection becoming a challenge.
Huawei's Liquid OTN technology introduces the use of the optical service unit container, with its bandwidth able to flexibly adapt to 2 Mbit/s, matching the granularity of traditional SDH services. Liquid OTN technology supports continuous lossless bandwidth adjustment from 2 Mbit/s to 100 Gbit/s (N x 2 Mbit/s), maximizing network resource utilization, and supporting differentiated latency levels. The Liquid OTN solution additionally reduces single-site latency by 70% through flattened network transmission layers. As a result, an optical transmission solution that utilizes Liquid OTN technology can provide bandwidth and latency assurance for an extensive variety of service applications, benefiting multiple vertical industries. Furthermore, due to the inherent hard pipe capability and stable service time sequence of OTN devices, Liquid OTN — which is an extended OTN standard with a transmission rate of less than 1 Gbit/s — inherits the architecture of traditional OTN. This is widely used in the transmission industry and, as such, a standardized, inter-connectable, and unified production network connection technology is achievable.
SDH and OTN are vital to global network infrastructure. As a next-generation technology, Liquid OTN can enable each industry to maximize the value of their transport networks. Liquid OTN directly supports fixed-rate optical services from 2 Mbit/s to over 100 Gbit/s, simplifying multiplexing layers. While best-effort SDH and OTN services can satisfy traditional industry production modes, this new small-granularity OTN technology is incredibly effective for new production and operation modes that require guaranteed bandwidth, low latency, and flexible optical connections.
In terms of market potential, market and research data shows that the global market scale of optical communication and network devices will be worth US$18.9 billion in 2020, and is expected to reach US$27.8 billion by 2025. The Compound Annual Growth Rate (CAGR) will remain at 8% from 2020 to 2025. The market scale of optical communication and network devices based on fiber channel technology is expected to peak within the forecast period. These forecasts signal that optical transmission technology and solutions will become more widely used for transport networks. As a supplement to OTN technology, Liquid OTN provides physically isolated small-granularity service transmission technologies, meeting the requirements for time synchronization and timely reachability of services on national and metro production networks. The physical isolation feature of Liquid OTN will allow future production networks to thrive.