Decoding OTN: The Super Engine Behind the 100G Construction of China's Three Major Carriers

Morning news on July 17 (Qi Ming) At the end of the last century, people once believed that 2.5Gb/s was the limit of optical fiber transmission. The "fiber revolution" initiated by former Nortel CEO John Roth brought humanity into the 10G era. More than a decade later, the former giant of optical communications has left the stage, yet the 100G era has arrived as scheduled. Large-scale deployment has already begun globally, and the 100G giant ship will carry human communications for the next decade.

Undeniably, the upgrading of optical signal rates has always accompanied the development of communications technology. The massive volume of services faced by communication networks moving toward ultra-broadband is the greatest pressure behind optical network upgrades. As the highway of communications, the optical transport network should naturally upgrade from 10G/40G to 100G. However, the speed of 100G deployment has still exceeded the expectations of many industry insiders. What has enabled this giant ship to ride the wind and waves toward large-scale commercial use?

Market Turning Point: Chinese Operators Significantly Drive the Maturation of the 100G Industry Chain

In its analysis report earlier this year, Ovum stated that in 2013, with the ramping up of 100G projects by Chinese operators, the world would truly enter a new 100G era. Objectively speaking, the rapid development of the 100G industry chain is inseparable from the technological innovation needs of Chinese operators and the industry push driven by the demand for massive bandwidth.

The original backbone networks of China's three major carriers were basically based on 10G or 40G wavelengths. Compared with China Telecom and China Unicom, which had already built 40G backbone lines on a large scale, China Mobile faced the greatest bandwidth pressure among the three operators. In 2012, China Mobile was the first in China to propose large-scale 100G network construction, with a construction volume exceeding the global total of 100G construction in 2011. This project became a turning point for global 100G commercialization and greatly stimulated the further maturation of the 100G industry chain. The project lasted one year starting from April 2012. All manufacturers went all out, each providing comprehensive 100G solutions—from 100G equipment to modules, components, and chips. Judging from the rigorous test results and subsequent commercial conditions, the 100G industry chain had matured. Subsequently, China Unicom conducted bidding for a 100G commercial trial network, and China Telecom also announced an even larger 100G procurement plan. The era of large-scale 100G construction had officially arrived.

Technology Engine: OTN Unleashes 100G Productivity

In 100G solutions, in addition to the line-side technology for 100G high-speed transmission, OTN cross-connect is extremely important to 100G networks. The two can be described as the twin engines of 100G technology and are the key technologies enabling the rapid development of 100G.

At the current stage, the service access rates for 100G networks are mainly 10G/10GE, with only the line rate adopting 100G. This requires mapping a large number of 10G small-granularity services into the 100G large pipe. The limitations of building networks using the 100G WDM approach are very prominent. First, end sites cannot access services freely. The line and tributary are tightly coupled—a specific line unit determines what tributary services it can carry. All services must be strictly planned, and new services require new wavelength channel design on the line side or the procurement of new units. Second, intermediate nodes cannot flexibly dispatch services. Services are fixed to their source and destination from the very first day of deployment. If changes are needed, manual patching of fiber connections at intermediate sites is required, or even additional hardware configuration, which is time-consuming and labor-intensive. Finally, the pipe cannot be utilized efficiently. The pipe and services are tightly coupled, and pipe resources cannot be shared across the platform. The 100G large pipe cannot be efficiently utilized, resulting in a huge waste of large-pipe resources. All services can only be transmitted point-to-point, and traffic across the entire network must follow fixed paths. Idle line bandwidth cannot be shared or multiplexed by services on other paths.

With the rapid development of cloud computing, streaming media services, and mobile broadband, bandwidth acceleration, dynamic changes, and regional imbalances are intensifying. This traditional point-to-point approach cannot efficiently and flexibly adjust services to meet the needs of operator networks. A 100G solution without OTN support is like a highway without overpasses—vehicles can only enter and exit the highway at fixed interchanges, unable to freely get on and off at different interchanges or be dispatched between different highways.

The essence of OTN is the decoupling of pipes from services and the decoupling of line from tributary. It represents a huge technological revolution in the WDM industry and is an advanced productive force. If this productive force was not fully realized in the 10G/40G era, with the arrival of the 100G era, OTN functions will be fully demonstrated and are unstoppable.

De-Telecom-ization: Impressive OTN Achieves Optimal Network Cost

OTN brings the electronic digital technology that has developed enormously in recent years into the traditional WDM optical communications field, using an optoelectronic integration approach to completely overturn the traditional point-to-point WDM architecture.

As is well known, Wei Leping proposed an important principle of "de-telecom-ization": "optimization of network cost." Operators have shifted from focusing on the cost of individual network elements to focusing on the optimization of the entire network cost.

OTN is an innovative case in the optical communications industry where technological innovation reduces network construction, operation, and maintenance costs. Its typicality is worthy of being included in telecommunications technology innovation textbooks. Through standardized processing of service and line-side signals, OTN achieves the decoupling of pipes and services, greatly simplifying the service logic of WDM networks. OTN enables flexible configuration of line capacity, flexible access and dispatch of multiple services, and provides comprehensive protection, thereby achieving refined operation of the 100G large pipe and making the 100G network controllable, manageable, and operable. At a time when network maintenance costs are rising sharply, its value stands out—it simplifies network service deployment and greatly reduces operational costs.

Compared with traditional WDM, OTN equipment only requires the addition of cross-connect boards and backplane buses. Compared with the system's 100G line cards and optical-layer components, the increased system cost is less than 2%, but bandwidth utilization, service provisioning efficiency, and operation and maintenance efficiency improve by more than 30%, greatly reducing network operation and maintenance costs. Thus, "optimization of network cost" is achieved, aligning with the trend of "de-telecom-ization."

After years of development and the rapid arrival of 100G, OTN technology has been widely accepted by the industry. In 2013, authoritative industry analysis firms Ovum and Infonetics both explicitly pointed out in their analysis reports that OTN technology and 100G technology are strongly coupled in the 100G era. Infonetics' latest OTN technology survey report from May 2013 shows that in 2013, 44% of customers worldwide had already used OTN technology to build WDM networks, and this proportion is expected to rise to 89% by 2016. The report also emphasized that with the development of high-speed line technologies such as 100G and beyond-100G, the combination of OTN and WDM is an inevitable trend in technological development.

Push from China's Three Major Carriers: 100G Will Strengthen the Application of OTN Technology

Not only China Mobile, but also China Telecom and China Unicom have raised the banner of OTN in their respective projects, pointing out the main course for the development of optical networks.

In fact, as early as the 40G era, China Telecom and China Unicom had already introduced OTN technology into 90% of new provincial backbone and metropolitan area network projects. OTN technology has long been recognized by the provincial companies of China's three major carriers for its flexible service dispatch and rapid service provisioning.

In 2012, China Unicom built an OTN 40G national backbone private network, providing unified dispatch and management for existing 10G/2.5G private line services, greatly optimizing the deployment and adjustment of private line services and improving response speed to major customers.

In 2013, China Telecom also began to change its traditional national backbone network construction model, introducing an equipment-integrated OTN dispatch plane on the basis of 100G WDM, specifically for integrating and dispatching small-granularity services and private lines within the 100G pipe.

In summary, the three major domestic carriers may differ in their approaches to OTN application, but there is no dispute whatsoever regarding the necessity of applying OTN technology.

Just as the technological revolution led by Nortel quickly brought 10G technology to market success, the long-term bandwidth hunger of backbone networks will accelerate the commercialization of 100G. The enormous value that the super engine OTN brings to networks is the driving force, and it will surely propel the 100G giant ship forward, fully demonstrating the technological charm of optoelectronic integration.