Pluggable coherent router optics such as 400ZR and 400ZR+ have caught the eye of operators looking to upgrade their networks to 400GE speeds. The prospect of a low-cost, high-density solution that lets IP routers directly interface with the photonic service layer allows operators to rethink future IP-optical network designs.
Less obvious, but not to be overlooked, is the impact of using colored router optics on current IP-optical management systems and operational practices. The use of conventional gray router optics in combination with DWDM transponders has maintained a clear demarcation between the IP routing and optical transport layers, allowing operators to manage each network layer in its own silo. When operators equip digital coherent optics in the IP routers, these established network boundaries are crossed and a transparent 400G dataplane emerges, allowing for closer integration of IP and optical transport layers.
IP-optical integration: A meeting of minds
The courtship between IP routing and optical transport started early in the millennium, with the convergence of all services on IP and Ethernet packet transport. Over time, IP routing and DWDM transport steadily pulled closer to unlock the potential synergies of combining these technologies:
- Generalized MPLS was adopted to power the optical transport control plane. It allowed operators to dynamically engineer, provision and restore flexible OTN and wavelength services.
- Hybrid packet-optical transport equipment integrated packet-grooming capabilities to fill wavelengths more efficiently, while IP routers integrated DWDM transponders on line cards.
- SDN became the catalyst for cross-domain coordination and the automation of the IP/optical management plane.
Despite these increasing commonalities, IP routing and optical transport kept living apart together in most operator networks, meeting casually where interests aligned but each minding their own business. Clear boundaries were drawn and responsibilities divided to foster a cooperative working relationship for their mutual benefit.
These boundaries are fading as a new breed of 400G pluggables based on QSFP-DD optics equip routers with coherent transmission capabilities that can extend to hundreds of kilometers. These pluggable optics provide the same port densities as conventional gray optics used to interface routers with coherent DWDM transponders in the optical transport network.
Pluggable 400G coherent optics essentially join IP and optical network layers at the hip, making a coordinated management approach essential to move forward in unison. It redefines the relationship between IP routing and optical transport and rearranges their responsibilities. Each still has individual roles and responsibilities, but they must work together to perform certain tasks as a team. Making the relationship work requires active listening and collaboration skills.
IP-optical coordination: Making ends meet
When pluggable coherent optics are equipped in a QSFP-DD or CFP2 cage, the router needs the smarts to detect and properly configure it. For a basic 400G router interconnect use case that involves connecting two coherent transceivers over a dark fiber, the router operating system needs to manage and monitor coherent optical interface parameters such as modulation, bit and baud rates, transmission and forward error correction performance. The router operating system must also be enhanced so that it can manage the coherent interface modules as a seamless part of its equipment inventory, and make them operationally accessible for external fault, configuration and performance management applications through open, model-driven interfaces.
Although integrated DWDM transceivers enable routers to become self-reliant for short point-to-point transport links, optical line systems remain critical for bridging longer distances and making optimal use of available wavelength frequency spectrum and fiber plant. IP-optical transport links in metro and regional networks may involve multiple fiber spans, optical line systems, in-line amplifiers and reconfigurable add/drop multiplexers (ROADMs). To set up 400G links, all IP routers and optical transport systems must literally be on the same wavelength. The emerging Open Line Systems architecture addresses this issue by providing unified management and control for terminal devices, be it pluggables or transponders provided on a line system.
Provisioning and assuring alien wavelengths for 400GE coherent routing applications over lit fiber networks are responsibilities that fall squarely in the optical management domain. However, the IP and optical management layers must coordinate channel selection, power balancing, grid spacing, filter settings, wavelength routes, physical diversity and restoration options. As the demarcation interface shifts from the electrical layer to the photonic layer, IP routers can no longer rely on tools such as the Link Layer Discovery Protocol to find cross-domain links to optical transport systems. They must interact with optical network inventory management systems to build a multilayer IP-optical topology view (Figure 1).
Figure 1. 400G coherent IP-optical management coordination
Operators also need IP-optical coordination to qualify fiber routes and determine the optimal coherent transceiver types and parameter settings to be used in the router, and to ensure fast and accurate failure resolution when lasers degrade or fibers break. When coherent transceivers equipped in a router detect excessive bit error rates or a loss of signal, multilayer alarm correlation will help operators pinpoint these issues in the physical or photonic layer.
Coordinating these tasks manually across isolated IP and optical management silos will prove to be cumbersome, error prone and time consuming. Unifying the management and control interfaces of optical services across IP routers and optical transport systems will circumvent some of the limitations that have always plagued alien wave deployments.
IP and optical: Better together
In the 400G era, IP routing and optical transport have even more in common and must interwork more closely and frequently than in the present 100G era. Networks are growing in scale and complexity, and traffic demands are becoming exceedingly dynamic and unpredictable. As IP routers cross over into the domain of coherent optical transport, they are exposed to new port and link management practices that were traditionally in the jurisdiction of the optical transport network. Operational tasks such as optical channel provisioning, connectivity discovery, maintenance and troubleshooting of optical connectivity must now also be incorporated into the scope of overall router management.
This shift will accelerate and intensify the need for flexible and powerful tools that can operate efficiently across layers, navigating and coordinating operational activities between the IP and optical worlds. Cross-domain management coordination becomes increasingly important as networks scale, and must be open to include third-party components in multivendor solutions.
Fortunately, industry initiatives such as the Transport Application Programming Interface (T-API), and model-driven network interfaces such as NETCONF/Yang and OpenConfig, have created a strong foundation for coordinated IP-optical management. The Nokia Network Services Platform (NSP) and its supporting optical management and control functions build on these open interface standards to offer a rich application suite for coordinating and automating IP-optical networks in multivendor environments.
If you’re interested in learning more, the following blogs are worth a read:
- Better coordination of operations across IP & Optical layers with SDN
- How to boost the efficiency of your operations with automation across IP and optical networks.
For a deeper dive into cross-domain IP-optical coordination, read our application note on achieving efficient IP-optical network automation with Nokia NSP.
