New developments in IP and optics are re-igniting discussion about IP-optical integration, as my colleagues described in the first two posts in this blog series (400G everywhere, IP routing for the 400G era). Standardization of the 400 Gigabit Ethernet (400GE) protocol is leading the industry to embrace 400G as the new currency for high-bandwidth router connections. Router ports designed to accept 400G pluggable optics can now use short-reach optical interfaces (also called “client” or “gray” interfaces) to further scale high-speed intra-data center connections.

More recently, these short-reach gray optics have been complemented by the availability of 400G pluggable coherent transceivers with wavelength division multiplexing (WDM) capability, which extend high-speed connections to much longer distances across the WAN. Network operators can now directly equip coherent WDM optics into the latest generation of 400GE-capable router ports and forgo the use of transponders implemented in a separate WDM transport system. This approach reduces cost, space and power requirements, and is of interest to network operators that want to increase network capacity while limiting costs.

All of this leads to two key questions. What are the use cases for IP-optical integration? And what IP and optical elements are required to enable an end-to-end solution that is more than the sum of its parts?

IP-optical network use cases

There are as many network types as there are network operators, but we can narrow these down to a few typical cases that vary based on the increasing complexity of their service connections and network scope (Figure 1). The first category covers applications that require simple point-to-point connection of multiple 400GE ports between routers. It includes campus networks, high-bandwidth access links and metro data center interconnect (DCI), and may extend to longer distances for regional DCI to enable data center virtualization. In such cases, the requirement for an IP-optical solution mainly calls for simple WDM aggregation of multiple 400G interfaces, and optical amplification whenever the link distance exceeds a few tens of kilometers .

Figure 1: Optimal IP-optical solutions should enable use across a wide range of network types.

Besides linear, point-to-point applications, viable IP-optical solutions must also accommodate a wide range of more complex network use cases. These include:

• Metro and regional aggregation rings that collect hub and spoke traffic from access nodes and central offices to one or more service hubs
• Metro core networks with any-to-any traffic connections between central offices (COs), internet exchanges (IXs) and co-location sites
• Regional and long-haul core backbones that interconnect cities and regions, along with widely disparate DCs and internet peering sites

In more complex network topologies, IP traffic doesn’t simply start and end at each routing node. It consists of complex, meshed, end-to-end service demands that generate high volumes of through traffic. Effective IP-optical network solutions should offer a range of connectivity and distance options that cost-effectively support the ability to add and drop services to and from multiple destinations, and support pass-through traffic that needs to transit intermediate nodes. It should provide these capabilities with minimal interface transitions between IP routing and optical transport layers. Network operators want IP-optical solutions that deliver end-to-end packet services seamlessly and efficiently, much like a multilane highway allows cars to merge and exit via on-ramps rather than having traffic lights at every exit.

To achieve this, network operators need to consider four key IP-optical building blocks necessary for providing optimal and versatile solutions across the full range of 400G network applications:

1. Pluggable coherent WDM optics in different form factors to meet cost and connectivity objectives
2. Suitable IP routers that are designed to support these pluggable coherent optics
3. Optical line systems that efficiently connect routers and multiplex wavelengths on fiber links
4. Multilayer IP-optical management and control software that supports seamless, end-to-end operation

Figure 2: A complete set of optimized IP-optical solutions enables more than the sum of its parts.

Router-pluggable coherent optics

Digital coherent optic (DCO) pluggable transceivers can be equipped directly in router ports to provide the scalable WDM capacity required to link high-capacity routers. As explored in our blog on IP routing for the 400GE era, 400G DCO transceivers support a range of options:

• 400ZR is designed for short-reach links up to 120 km.
• 400ZR+ adds multi-rate capability and extends reach.
• 400G Multihaul transceivers further expand capacity–reach capability, add service provider-oriented features and support pass-through traffic for multiple nodes using reconfigurable optical add-drop multiplexers (ROADMs).

The incremental capability of 400G Multihaul DCO transceivers makes them an important element in a portfolio of IP-optical solutions. Their longer reach extends the application space of IP-optical applications into metro and regional networks and across longer distances. It also enables optimized router bypass through intermediate nodes, allowing end-to-end traffic demands to avoid unnecessary router transits.

Ultimately, 400G pluggable DCO transceivers may not be able to meet the capacity–reach requirements of every link in the network. IP-optical applications that span long distances, such as national IP backbones and transcontinental networks, may require 400G connections across links that stretch 1,000 km and more. These are best implemented using the latest generation of transponder-based coherent optics, such as the Nokia PSE-Vs, which is optimized for maximum capacity–reach performance to support 400G Anywhere.

Optimizing routers for IP-optical integration

Routing platforms are judged across a wide range of attributes unrelated to optics. However, the ability of routers to successfully integrate pluggable 400G DCO transceivers is a critical part of any successful IP-optical solution. Nokia’s market-leading service routers, based on the FP4 family of scalable, programmable packet processors, are notable for having enabled the first commercial deployment of 400GE interfaces. They have been engineered with IP-optical integration in mind. Their design addresses two important requirements for successfully integrating 400G DCO transceivers: thermal management and interface diversity.  

Power consumption and heat dissipation are higher for 400G pluggable coherent optics than for short-reach client optics. Power and cooling of line card cages can become an issue for routers designed to maximize switching capacity and interface density. The thermal design of 400G-capable line cards is thus a critical element for coherent IP-optical integration. It determines a router’s ability to efficiently cool all interface ports, including pluggable 400G coherent optics.

Nokia’s router design practices prioritize efficient thermal management with features such as dual-sided line card printed circuit boards (PCBs) to avoid stacked optics cages, a large dedicated heatsink for each cage to improve cooling, and air guides to ensure even and unobstructed airflow. This combination of features means that Nokia routers can accept the complete range of pluggable 400G DCO transceivers without limitations such as dedicated slots, equipping rules or leaving some ports empty.

Routers need to support the full range of 400G pluggable form factors to enable IP-optical solutions across all network use cases. While 400ZR and 400ZR+ in QSFP-DD formats can be equipped in the same router ports as short-reach client optics, their capacity–reach performance limits their use to short- or medium-reach point-to-point links for access and metro DCI applications.
 
Nokia routers also support interface cards with CFP2 ports. This enables operators to use pluggable 400G Multihaul optics to provide superior capacity–reach performance for metro and regional applications, and to transit multi-node links with ROADMs at intermediate sites.

Nokia routers also enable operators to interwork router-pluggable coherent optics with transponder-based optics over common network links to allow further optimization based on end-to-end service demands. By providing the ability to mix and match coherent interface options with different form factors, Nokia platforms enable operators to make optimal use of 400G as a single network currency across all network applications (Figure 3).

Figure 3: A complete range of 400G coherent optics in routers and transponders enables 400G anywhere.

Application-optimized optical line systems

The next consideration is how to best interconnect routers with 400G coherent optics over a fiber network. Efficiently connecting routers over fiber is the task of the optical line system, which implements a collection of important functions, including:

• Multiplexing/de-multiplexing multiple WDM channels onto a fiber
• Optical amplification at endpoints and intermediate sites to boost optical power levels for greater reach
• ROADMs that can route and switch 400G coherent links as needed to optically bypass intermediate router nodes and avoid the unnecessary consumption of router capacity for transit traffic

The Nokia 1830 PSS family provides a full range of line system options to enable optimal configurations for all IP-optical network use cases. Targeted features such as WDM mux/demux and amplifiers can provide operators with a compact and cost-efficient solution for DCI and other simple point-to-point applications. For more complex networks, operators can add features such as ROADMs to enable optical bypass in metro aggregation rings, or for multi-degree nodes with a large number of ingress/egress directions. The 1830 PSS also enables operators to optically bypass intermediate router nodes where and when needed. This makes it easier to reengineer and optimize IP-optical links to efficiently accommodate network growth, changing demand patterns, and planned or unplanned network outages.

The key to tying routers, pluggable coherent optics and line systems together to create a deployable IP-optical solution is to integrate them into a unified end-to-end network management, control and automation platform. The next blog in our series will delve into Nokia’s solutions in this area.

Conclusion

To create 400G IP-optical solutions that are more than the sum of their parts, operators need a complete set of hardware and software building blocks optimized around the new network currency of 400G. These solutions should include a range of pluggable coherent optics, routing platforms optimized for 400G coherent pluggable transceivers, multifunction optical line systems, and multilayer, end-to-end management.

When combined and deployed in synergy, these building blocks give network operators flexible options for addressing a wide range of network use cases without making trade-offs in cost or performance. This helps operators avoid the need to over-design IP-optical solutions for short, point-to-point access and metro links, or to overspend on inefficient architectures or underperforming optics in more complex metro, regional and core networks. With the ability to choose and combine the right options in each instance, and evolve, expand and upgrade when needed, operators can ensure that they will realize the expected benefits of IP-optical integration.
 

Learn more

Technology: Coherent Routing
Technology: PSE Super Coherent Technology
Technology: FP4 network processor
Solution: IP-optical coordination
White paper: The 400GE inflection point