I. Introduction

• The Broadband China/Optical Network City Plan and its implications.
• The limitations of 40G OTN and the emerging need for 100G OTN technology.

 With the implementation of the Broadband China/Optical Network City Plan, OTN transmission systems have been deployed on a large scale in backbone networks. However, it is not difficult to see from the explosive development trend of business capacity that 40G0TN will also be stretched when carrying multi-services in the future. , so the demand for 100G OTN ultra-high-speed transmission technology is imminent.

II. Features of 100G ONT Technology

1,OSNR Performance Improvement

• • Introduction to PM-QPSK with coherent detection.
  • The benefits of transferring light wave phase information to the digital domain.

PM-QPSK with coherent detection provides approximately 6dB sensitivity improvement in optical signal-to-noise ratio over binary (00K). The capacity of 100G OTN is 10 times that of 10Gbit/s, so the 1 OOGbit/s modulation scheme needs to provide 10dB higher performance than the 10Gbit/s 00K code type. The key advantage of coherent detection is that light wave phase information can be transferred to the digital domain, so that powerful electronic dispersion compensation (EDO) capabilities can be used to clean up signal distortion at a very low cost.

2,Chromatic Dispersion (CD) Tolerance

• The role of modem chips with electronic dispersion compensation (EDC).
• Advantages of using dispersion compensating fiber (DCF) in OTN deployments.

Modem chips with electronic dispersion compensation (EDO) function do not require an external tunable dispersion compensator.

The total amount of chip dispersion compensation is determined by two factors of the finite impulse response (FIR) adaptive filter: tap quantity and the amount of delay.

OTN deployments mainly utilize dispersion compensating fiber (DCF) to limit the residual dispersion to 10Gbit/s 00K receiver tolerance (usually +/-400ps/nm), and in this range 100Gbit /s PM-QPSK EDC is easy to do.

3,Polarization Mode Dispersion (PMD) Tolerance

• The dynamic nature of PMD changes.
• Differences between dispersion and PMD compensation.

Modem chips with electronic dispersion compensation (EDC) can also be used for PMD compensation. A key to PMD compensation is the need to track changes in high-speed polarization dynamics on the network very quickly. This is very different from dispersion compensation, because the change in dispersion is relatively static (the amount of change is very slow and small), usually caused by changes in fiber temperature.

4,Phase Modulation

• The significance of QPSK technology.
• Impact on signal baud rate and 50GHz spacing OTN systems.

The widespread application of phase modulation in 40G systems further promotes the maturity of this technology in 100G OTN. The use of QPSK technology can double the amount of information carried by optical carriers.

Combining with polarization multiplexing reduces the 100G signal baud rate to about 25Gbaud/s, so it can be applied in 50GHz spacing OTN systems and also reduces the Signal requirements for fiber nonlinearity tolerance.

5,Polarization Multiplexing

• Basics of how polarization multiplexing works.
• Its engineering applications and importance in 100G OTN.

The mutual orthogonality between the two polarization states of the optical signal is used to carry two channels of information on the same optical carrier, which reduces the signal element rate by half. Polarization multiplexing is a relatively mature technology that has been used in engineering applications in 40G systems, and has become an indispensable technology for 100G OTN.

Polarization multiplexing only requires some relatively simple passive components for the transmitter, and the difficulty lies mainly in the depolarization part of the receiver.

III. Current Key Technologies and Applications of 100G OTN technology 

1,Interface Technology

• • Distinguishing between physical and logical interfaces.
  • The standardization efforts by ITU-T for these interfaces.

The interface technology of 100G OTN mainly includes physical interface and logical interface.
points, of which the logical interface is the most critical part. For physical interfaces,
ITU-T G.959.1 has standardized the corresponding interface parameters, and for logical interfaces,
ITU-T G.709 specifies the corresponding overhead bytes of different electrical domain sub-levels, such as
Optical path transport unit (OTUk), ODUk (including optical path payload unit (OPUk))
etc., as well as the management and maintenance signals of the optical domain. Among them, OTUk is equivalent to the segment layer, ODUk is equivalent to the channel layer, and ODUk includes 6 serial connection monitoring overheads that can be set independently.

2,Networking Technology

• The versatility of 100G OTN technology in network configurations.
• Current implementations by manufacturers.

100G OTN technology provides 0TN interface, ODUk cross-over and wavelength cross-over functions, and has the ability to form a network in the electrical domain, optical domain or electrical domain and optical domain. The network topology can be point-to-point, ring network and mesh network wait.

At present, the typical implementation of OTN equipment is to use 0DU1 cross-over in the electrical domain or wavelength cross-over in the optical domain.

Among different manufacturers, there are fewer implementations using the electrical domain or electrical/optical domain combined methods, and more implementations using the optical domain method. 

3,Protection and Recovery Technology

• Electrical vs. optical domain protections.
• The adaptability of control plane-based protection and recovery in OTN networks.

100G OTN technology can support different protection and recovery technologies in the electrical domain and optical domain.

The electrical domain supports ODUk-based subnet connection protection (SNCP), ring network sharing protection, etc.; the optical domain supports optical channel 1+1 protection (including 1+1 protection based on sub-wavelengths), optical channel sharing protection and optical multiplex section 1 +1 protection etc.

In addition, control plane-based protection and recovery are also applicable to OTN networks.

4,Transmission Technology

• The essence of optical transport networks.
• How 100G OTN integrates innovative transmission technologies for improved capabilities.

Large-capacity and long-distance transmission capabilities are the basic characteristics of optical transport networks.

Any new optical transport network must continuously adopt innovative transmission technologies to improve corresponding transmission capabilities, and OTN technology is no exception.

In addition to using out-of-band FEC technology to significantly improve the transmission distance, 100G OTN currently adopts new modulation coding (including intensity modulation, phase modulation, intensity and phase combined modulation, modulation combined with polarization multiplexing, etc.) combined with dispersion ( Technologies such as optical domain adjustable compensation (including chromatic dispersion and polarization mode dispersion) and electrical domain equalization have significantly increased the networking distance of 100G OTN networks in high-speed and large-capacity configurations.

5,Intelligent Control Technology

• Comparing OTN to SDH-based Automatically Switched Optical Network (ASON).
• Distinct bandwidth considerations for intelligent function scheduling.

The intelligent control technology based on the control plane of 100G OTN includes similar requirements to the SDH-based Automatically Switched Optical Network (ASON), including automatic discovery, routing requirements, signaling requirements, link management requirements, protection and recovery technology, etc. SDH-based ASON-related protocol specifications can generally be applied to OTN networks.

The key difference with SDH-based ASON networks is that the bandwidth for intelligent function scheduling and processing can be different, the former is VC-4, and the latter is ODUk and wavelength.

6,Management Functions

• Meeting the requirements of OTN technology.
• Evolution of OTN network management systems based on traditional WDM systems.

In addition to meeting the general requirements for configuration, fault, performance, and security functions, the management of 100G OTN also needs to meet the specific requirements of OTN technology, such as OTN-based overhead management, ODUk/wavelength-based scheduling and management, and wavelength-based power.

Balance and control management, wavelength conflict management, OTN-based control plane management, etc. Current OTN network management systems are generally upgraded based on the original traditional WDM network management system.

In addition to conventional management functions, they can also support corresponding basic management functions of OTN.

7,Integration of 100G OTN with Other Networking Technologies

• Viewing 100G OTN as a TDM technology.
• The emergence and potential of P (packet)-OTN or E (Ethernet)-OTN concepts.

100G OTN technology is essentially a TDM technology, and the main customer services currently transmitted are packet services.

Therefore, taking into account various factors such as bandwidth utilization, energy consumption, and application scenarios, 100GOTN technology will be compared with other existing transmission services. Networking technologies have achieved a certain degree of integration.

For example, 100G OTN technology can incorporate some functional requirements at the Packet Transport Network (PTN) or Ethernet level, and correspondingly evolve a new generation of 100G OTN technology that is different from existing OTN technology, such as The network structure of the current P (packet)-OTN or E (Ethernet)-OTN concept.
(A) The application of OTN technology is gradually unfolding from point to surface
At present, the main applications of 100G OTN technology (typical ODUk crossover)
Focusing on provincial trunk lines and metropolitan area transmission networks, with the 100G OTN technology, standards.

Equipment and test instruments are becoming increasingly mature, and the application of 100G OTN will be fully developed.
With the development, the application network scope is mainly metropolitan core, intra-provincial trunk lines and inter-provincial trunk lines.

At the same time, metropolitan aggregation and access will also be applied to a certain extent, and intelligent control planes will also be introduced at appropriate times.

IV. The Evolution of OTN Technology Applications

• The current focus of 100G OTN applications.
• The potential expansion into metropolitan cores, intra-provincial trunk lines, and more.

V. Conclusion

• The potential future of 100G OTN in the context of optical transmission systems.
• The direction of development for 100G OTN equipment, emphasizing capacity, distance, and intelligence.

To sum up, from the perspective of OTN technology itself, 100G OTN will build an expanded next-generation optical transmission system based on the existing optical transmission system in the future, and at the same time define the customer service mapping methods involved in the new optical transmission system develop.

From the perspective of the development of OTN equipment, driven by the gradual improvement and increasing application of OTN technology, 100G OTN equipment continues to develop in the direction of large capacity, long distance and intelligence.