The concept of an alien wavelength is a long-standing one in optical line systems. Disaggregation brings architectural advantages in engineering, building and incrementally updating networks, but it also introduces the complication of alien wavelengths.

Operators I have spoken with see this situation as suboptimal but necessary to advance their networks with the latest gear at the lowest cost. As shown in the diagram below, the issue is the fact that parallel network management systems have segmented views of the end-to-end wavelength, making many automated, end-to-end operations more difficult and error prone than they would be if they were managed with a single NMS.

In this context, an alien wavelength is defined as transparent transmission of colored optical channels over preexisting third-party physical infrastructure. The name alien is well chosen in the sense that the alien wavelength is a foreign entity on the line system. In the management system of the diagram’s Vendor A, only basic spectral characteristics of the channel are known. As a result, certain holistic management functions (e.g., power management, assurance and fault diagnosis) become difficult or impossible to carry out. The introduction of pluggable coherent optics, while bringing many advantages in cost and power consumption, creates a channel that is inherently alien because of the independent nature of the IP and optical management systems. This would not be the case if Vendor A’s management architecture allowed for a fully managed wavelength.

Domain controllers and open interfaces

A domain controller architecture with open, standardized interfaces, like the one shown below, brings many operational advantages. For example, this architecture permits end-to-end wavelength visibility and control, which removes the constraints and complexities of dealing with alien wavelengths, even in multi-vendor, multi-domain deployments.

The key components of this architecture are the Transport-API (T-API) and the use of standard modeling languages and associated protocols such as NETCONF/YANG. The IP controller can initiate a new 400ZR link, retrieving the critical optical parameters such as channel and power level from the optical domain controller according to planning information. Database consistency is maintained at all times through the T-API interface. Legacy vendor equipment can be managed through adapters where required.

The benefits of avoiding aliens and more

Nokia supports this open domain controller architecture across many products, including the Network Services Platform (NSP), which provides IP management and automation, and the WaveSuite network operations center (NOC), which acts as an optical domain controller. This provides many benefits in the IP-optical domain:

• Coherent pluggable optical devices can be seamlessly introduced in addition to black-and-white interfaces to enable combined IP-optical networking.
• Optical services can be planned and commissioned, even in mixed transponder and ZR+ deployments.
• The non-alien architecture can be used to support many valuable end-to-end lifecycle operations, including comprehensive power management, link discovery and connectivity verification.  
• A uniform multi-vendor management and troubleshooting capability can be applied to all optical services, whether they originate on transponders or router pluggables.
• Quality of service performance guarantees can be established and service-level agreements can be implemented, rather than simply allocating spectrum.
• Alarms can be correlated across the IP and optical layers, which expedites troubleshooting for transponder-based and 400ZR-based channels.
• Layer 0 connectivity between routers and optical gear such as ROADMs can be automatically discovered.

As you can see, the architecture’s utility goes beyond the issue of dealing with alien wavelengths. It can also support high-value use cases in the areas of discovering network topologies, correlating across IP and optical layers to gain deeper actionable insights, and optimizing for efficient and effective network engineering operations.

Want to know more? Check out our extensive catalog of multilayer network automation use cases. And read our application note for an in-depth look at how the Nokia NSP manages the automation of 400GE pluggable coherent optical devices. You can also visit our web page to learn more about how the Nokia NSP simplifies IP-optical coordination.