Discussion on 40G to 100G WDM Network Upgrading
This paper summarizes the problems found in the deployment and maintenance of the existing WDM transmission platform in China, especially the 40G system, and explains the reasons why the WDM network should gradually stop 40G network construction and evolve to 100G network from the perspective of business growth and transmission technology. At the same time, we made some comments and suggestions on 100G network construction mode, network technology applications, network maintenance precautions and so on.
Discussion on 40G to 100G WDM Network Upgrading

The long-distance transmission network of China Telecom has been built for many years, which has been constructed with wide coverage, high bandwidth and perfect structure for wavelength division multiplexing platform. With the implementation of the “Optical Network” program, the speed and quality of the data network are driven by the new bandwidth application, such as mobile Internet and cloud computing, to a large extent affect the business income of telecom operators. It is estimated that 2016 telecom operators in China and other regions will be an urgent need for 100G applications, 2017 will be extended to the country’s major core nodes and parts of the city’s export nodes. Although the scale has been deployed 40G platform, to build an ultra-high-speed network to meet the needs of business development, telecom operators WDM network to 100G forward construction and deployment will be imperative.

Existing problems of 40G WDM Network

Since 2009, telecom operators have been building 40G wavelength division multiplexing network, effectively relieved the bandwidth pressure, but from the maintenance practice in recent years, compared with the 10G platform, it has put forward stricter requirements in the aspects of business opening, daily performance maintenance, and optical cable maintenance, and there are many insurmountable problems. Mainly in the following areas:

• The client transmission distance is limited
At present, the 40G wavelength division multiplexing client-side interface is usually configured with a 1550nm wavelength NRZ (Not Return to Zero) interface, the G.652 fiber client side dispersion tolerance is only 2km, the G.655 fiber dispersion tolerance supports the only 10km, there is no corresponding solution for more than 10km. And because of the reasons for the data center room, 40G data equipment nodes and 40G wavelength division multiplexing nodes are usually not in the same room, the trunk cable between the two mostly G.652, relay distance is much larger than 2km, in order to successfully open 40G following the business, you need to be equipped with a large number of relay systems, which not only huge investment, but also increased the risk of hidden dangers and daily maintenance workload.

• The daily performance maintenance is very difficult
40G daily maintenance and 10G is concerned about the channel OSNR (Optical Signal Noise Ratio) and other indicators. Because the 40G wavelength division multiplexing uses the new code type, the spectrum is wide, the peak power and the actual power have a big difference (the difference is 6~8dB), needs to pass the integral method to carry on the measurement OSNR. But the current network management does not support the OSNR directly on-line measurement, commonly used in the 10G system, the spectrum analyzer cannot continue to use the interpolation method can provide 40G test instrument manufacturers are not many, to the maintenance of the daily system And fault location has brought great inconvenience.

• System protection is weak, fiber splicing and system scheduling difficulty
40G relative to 10G, the OSNR tolerance is reduced by 6dB under the same physical conditions, the chromatic dispersion tolerance is reduced by 16 times, PMD (Polarization Mode Dispersion) is degraded by 4 times, and the nonlinear effect becomes more obvious. This brings two problems: First, it is difficult to protect the system through the configuration of optical fiber optic cable OLP (Optical Fiber Line Auto Switch Protection Equipment), because the dispersion tolerance of 40G optical module is only about 100ps / nm, OLP protection requires detailed dispersion testing of fiber and DCM (Dispersion Compensator Module) modules, making the active and standby routing dispersion accurate to the 40G optical module’s dispersion tolerance, the network design is very difficult.

The second is fiber splicing and system scheduling difficulty. In order to complete a line adjustment or system scheduling involving 40G system, it is necessary to strictly calculate the conditions that the spare core should be prepared for the three aspects of attenuation, residual dispersion and PMD tolerance in advance, and formulate the fiber splicing scheme. This is not only difficult in time to deal with sudden scheduling or fault repair needs, but also do not meet the current lack of cable resources, the real conditions. In fact, in recent years has occurred many examples that cannot be scheduled through the fiber optic cable scheduling 40G system to bring loss to the business.

Therefore, in addition to solving some of the bandwidth growth requirements, 40G has not brought more benefits, coupled with 40G technology development has reached an end, the industry chain participation and maturity of the problem, in fact, has become a transmission network development process of a transition technology.

Why Build 100G WDM Network

• Business growth demand for 100G
According to business forecasts, the next five years, the annual growth rate of transmission backbone network traffic will be as high as 60% to 70%. Guangzhou, Shenzhen, Dongguan, Foshan and other major data nodes on the 2016 and future 100G business needs than the previous forecast has been enlarged, which means that after five years of backbone network bandwidth requirements will be more than 10 times the current backbone transmission network. The total bandwidth will reach more than 200Tbps.

• Continuous development of transmission network demand for 100G
Relative to 40G, 100G technology from the proposed to the equipment mature development very quickly, in the standard follow-up, technical solutions, the development of the industry chain has done a better job to meet the bandwidth growth and network flexibility operation, convenient maintenance needs, is the development direction of the transmission network.

100G test instrument manufacturers support more than 40G greatly improved. JDSU, ANRITSU, EXFO and other manufacturers can provide 100GE online analyzer, but also supports OTU4-based OTN protocol analysis, including cost verification, alarm analysis, performance statistics and other functions. For the 40G wavelength division multiplexing cannot be measured online through the network management OSNR, most manufacturers also have a corresponding solution, such as Huawei’s SOM solution to support 100G OSNR online real-time monitoring, while the visual interface allows the system OSNR performance at a glance, Can greatly improve the efficiency of operation and maintenance.

In the client side interface transmission distance. At present 100G application in the trunk of the client side interface is mainly 100GBase-LR4/100GBase-ER4 SMF LAN interface, its shortest distance has 3km, the longest has 40km, the maximum degree of compatibility with the 10G system, to resolve the 40G customer side interface distance is the longest only 10km problem.

In the customer side interface transmission distance. At present, the customer interface of the 100G backbone network is mainly 100G Base-LR4 / 100G Base-ER4 SMF LAN interface, the distance is 3km, the longest is 40km, the maximum compatibility with the 10G system, to solve the problem that max distance can only reach 10km for 40G customer side interface.

In terms of system construction requirements and protection functions. 100G transmission through the use of PDM-QPSK (Polarization Division Multiplexed Quadrature Phase Shift Keying), in the receiver using coherent detection and DSP (Digital Signal Process) technology for dispersion and PMD compensation, compared to 40G, The transmission performance of the system has been greatly improved. Almost no need to consider the chromatic dispersion of optical fiber and polarization mode dispersion problem can eliminate the fiber optic cable DCM module, greatly simplifying the 100G network. PMD margin also enhances the 100G for a variety of old fiber applicability, making OLP protection possible.

In summary, the future evolution of WDM network should be to gradually stop the construction of new 40G network, and to maintain the existing 40G network basic stability and make appropriate expansion to meet the high level of business platform and 40G granular data business continuity requirements based on the early start of the construction of 100G network, and ultimately the formation of the main 10G and 100G-based network coverage.

The Deployment and Maintenance of 100G WDM Network in Future Telecom Operators

•  The new 100G network core node optimization and networking model
At present, Guangzhou has always been one of the core nodes of the transmission network and business. Huizhou, Shantou, Zhanjiang and other cities generally serve as an important transit node, and its own business volume is not large. On the contrary, the great volume of Shenzhen in the transmission network has been relatively marginalized. After several years of network adjustment, Guangdong Province, the data network has been formed to Guangzhou, Shenzhen as the core, other cities through the Guangzhou and Shenzhen to carry out business convergence and export network structure, this two-node centralized network model for long-distance backbone Network of the provincial core node security, business scheduling capabilities demanding, Shenzhen alone as a general business floor of the traditional transmission network ideas are not realistic. Therefore, in the new wavelength division multiplexing network construction and optimization process, Shenzhen must refer to the same status with the Guangzhou core node to plan, a substantial increase in its business to the local city capacity.

Network mode should give full play to the technical advantages of 100G wireless relay transmission distance to reach 1500km (20x22db), because this will make the system design and business opening more simple, to meet the data business point-to-point centralized open requirements. So on the network structure, it is recommended to reference the data network structure, to Guangzhou, Shenzhen as the main point, the rest of the city in a chain-like way directly converge to the main point; at the same time, in order to ensure the safety of the city to Guangzhou, Shenzhen, it is suggested that on the basis of direct-attached, the city increased by 1 to 2 of the connecting points to In the direct system failure can be easily scheduled or business circuitous.

• Application of network protection mechanism
On the transport network Protection scenario, it is recommended that you deploy the following two areas:

The intelligent function is partially turned on on the network. The intellectualization of transmission network is only widely used in Ason network, but there is no large-scale application in WDM network, and its construction is of high demand for cable line resources. However, the lack of intelligent function makes the OTN network business Open time short, the advantages of high resource utilization have not been played, resulting in insufficient transmission network flexibility, difficult to achieve easy management, customer-oriented network construction, and operational maintenance objectives. Therefore, it is recommended to open the intelligent part of the channel in the planning and construction of 100G. On the one hand, it can be used to open some high bandwidth customer service with higher security requirements; On the other hand, the function of the intelligent plane can be further validated, and the data service security after the business rerouting is validated by planning software, which will lay a good foundation for the scale application of intelligent plane in the future.
Introduce OLP line protection function. OLP line protection does not involve the high-level equipment and the agreement, may realize the business protection within 50ms, reduces the maintenance pressure. 100G is insensitive to dispersion, making the choice of OLP standby routes simple, essentially consistent with the 10G system. The OLP work of 10G WDM system is also proved to be good as long as the selection and test of standby line are done in the stage of planning and construction, it is feasible to introduce OLP line protection function in the 100G network.

• Network interface configuration
In the network interface configuration, because of the 100G signal’s input power, dispersion tolerance, PMD tolerance and other parameters and 40G signal, there is a discrepancy in the requirements of the WDM system, so it is not recommended to configure 40GE interface.

• 100G System maintenance Precautions
The maintenance object of 100G network not only contains the optical passive device and wavelength conversion unit of traditional wavelength division multiplexing domain, it also includes the Cross Connection Unit and the branch unit of the electric field, which requires that in the daily maintenance, we should be familiar with all kinds of alarms of the otn when we pay attention to the optical power, gain flatness, OSNR and other light layer parameters. The OTN alarm information and the signal flow are combined to locate the fault.

Another concern is resource management. The most headaches in the past are linked outages, not what business is running on the link. With more and more business integration technology and smart pipeline technology, a customer-oriented, accurate reflection of the network situation of the resource system can be quickly and effectively deployment of physical resources, in the event of network failure to help the maintenance staff to pinpoint the impact of the business scope, the rapid implementation of specific business recovery.


The new 100G OTN network can effectively alleviate the operation and maintenance pressure of WDM platform, improve the operational capability of the transmission network and the capacity of carrying, dispatching and management of High-bandwidth IP service, and realize the sustainable development of the network. Because 100G technology is still developing and perfecting, its deployment and maintenance need to continue to grope and summarize in practice.
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