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Blurred Operational Boundaries in IPoDWDM

portrait of Teresa Monteiro

June 29, 2023
By Teresa Monteiro
Director of Solutions, Software and Automation

And how to recover lost demarcation between the IP and optical domains

IP traffic over DWDM systems has been a major driver for the network capacity surge of the last few years, with bandwidth growing at a compound annual growth rate (CAGR) of more than 35% (ACG Research, 2021). This has led our industry to explore convergence of the IP service layer and the optical transport layer for network architecture simplification, including through the physical integration of a pluggable DWDM module into a router, known as IP over DWDM (IPoDWDM).

IPoDWDM eliminates the need for grey interfaces and transponders between routers and DWDM line systems, potentially bringing significant savings not only in terms of CapEx, but also in power consumption and footprint.

The concept of IPoDWDM is not new, but its wide adoption has only recently been made possible by significant advances in optical pluggables, such as the miniaturization of opto-electronics, improved power efficiencies, and the increased reach of coherent optical technologies.

But mainstream adoption of IPoDWDM won’t move far without a network management framework that is robust and scalable and fits well with the operational practices and strategies of communication service providers (CSPs).

What’s the problem?

One of the first concerns of IPoDWDM operation arises from the fact that, traditionally, the IP and optical transport domains have been managed independently. A common practice at CSPs is for the IP and optical domains to be managed by separate organizations, with separate tools, sometimes with little interaction between one another.

Figure 1: Top challenges for managing coherent pluggable optics in non-traditional optical platforms

A 2022 Heavy Reading operator survey identified “Maintaining the existing operational practices of IP/routing and optical domains” as the top challenge for managing IPoDWDM (Figure 1).

As optical engines move into IP devices and the clear demarcation between IP and optical is blurred (Figure 2), who is responsible for what, and what’s the right IPoDWDM management framework?

Figure 2: The loss of demarcation between the IP and optical domains

Meet TIP OOPT MANTRA

Telecom Infra Project (TIP)’s Open Optical and Packet Transport project subgroup MANTRA (Metaverse Ready Architectures for Open Transport, formerly known as CANDI, Converged Architecture for Network Disaggregation & Integration) was formed to address this and other challenges of IPoDWDM operations and to accelerate development and deployment of open converged packet and optical networking solutions.

Much like the TIP OOPT MUST work that I described in a recent blog, operators and vendors are jointly working in MANTRA to identify real-world use cases for IPoDWDM technology and define reference management architectures for these networks. These architectures should support full management for IPoDWDM scenarios, including network discovery, provisioning, performance monitoring, troubleshooting, alarms, and equipment and service inventory, and they should enable end-to-end network visualization.

MANTRA’s initial whitepaper was published a few months ago, and I encourage you to check it out. This whitepaper proposes two possible high-level target control architectures for IPoDWDM, which are currently open for discussion with vendors and members of the TIP community. These architectures rely on the existence of an IP controller, an optical controller, and a hierarchical controller (orchestrator), and differ in how the optical management responsibilities are split among them.

In both architectures, the coherent pluggable configuration is achieved through the northbound interface (NBI) of the IPoDWDM router using OpenConfig. TIP is highly focused on the use of standard approaches for open networking, and OpenConfig defines a set of mature vendor-neutral data models for network devices, including for optical pluggables. There are currently four parameters that have been defined: central frequency, output power, operational mode, and admin state.

In MANTRA Solution 1, the management of the pluggables in the router is shared between the IP controller and the optical controller. The IP controller is the only entity configuring the coherent pluggables, but the optical controller can also access the IPoDWDM router NBI, though this is limited to read-only permissions. Read access to the pluggables allows the optical controller to do device discovery, performance monitoring, and fault management. Since the optical controller consolidates all optical topology and services information, it is able to perform end-to-end path computation and define services to be provisioned, including the pluggables’ operational mode given the impairments in the line system path.

By contrast, in MANTRA Solution 2, the IP controller is the only entity that directly interfaces with the IPoDWDM routers. In this solution, the hierarchical controller has a more active role: it orchestrates workflows, combining topology, alarm, and performance information from the IP controller (responsible for the pluggable line interfaces) and the optical controller (responsible for the line system), and may even be responsible for computing end-to-end wavelength paths and modes. Depending on the network scenario and requirements, the role of the hierarchical controller may become more demanding and require considerable intelligence in optical networks – for example, to support dynamic reconfiguration of pluggable operational modes to adjust to changes in the line system path, triggered by performance degradation or restoration.

Outside of MANTRA

A dual IPoDWDM management architecture where both the IP controller and the optical controller access the router NBI and are able to configure the pluggable can also be considered. Both MANTRA proposals limit the solution to only one controller, the IP controller, configuring the router, to avoid any possible database synchronization issues. But the potential issues associated with dual controllers configuring a router can be mitigated by using strategies already defined in our industry, e.g., in IETF RFC 8341, used in a recent OFC demo, or simply by a strict and unambiguous separation of what is configured by one or the other controller, e.g., packet parameters versus optical parameters. In fact, Infinera has been successfully deploying this type of architecture in the field for several years.

Another pluggable management architecture that deserves your attention is the one specified in the Open XR Forum. It is particularly valuable as the types of coherent optical pluggables become diverse, and so do the hosts they are deployed in (routers, but also servers, radio units, etc.). The Open XR Forum proposes a dual management approach where common router NBI management is used for basic pluggable functions, but it is complemented by host-independent management for optical configuration, including advanced functions like probabilistic constellation shaping or point-to-multipoint network configuration. The host-independent management path is achieved by establishing a direct IP connection between the optical controller and the pluggable that does not require explicit support in the router OS and NBI. This is an innovative and very powerful idea that I plan to explore in more detail in an upcoming blog.

Everything you need…

As you see from the examples above, the topic of IPoDWDM management, as with optical pluggables themselves, is evolving. A number of control architectures have been outlined and are being discussed in TIP OOPT MANTRA and other industry forums, such as Open ROADM, OIF, and Open XR Forum. Is there, or will there ever be, one solution that fits all use cases, modes of operation, coherent optical pluggables, and routers in the market?

Figure 3: Several alternative IPoDWDM management architectures under discussion

We have been having many lively discussions with operators about this subject. Some operators are adamant that their IP team needs to keep absolute and exclusive control of router access. Others believe that their IP team will be more than happy for optical experts to continue to own and operate the full optical domain, including coherent pluggables. Some operators, knowing that end-to-end DWDM channels transmitted by traditional transponders will coexist with IPoDWDM in their networks, want similar management workflows for transponders and pluggables. But the most important takeaway is that operators are looking for vendors to partner with and explore the potential of IPoDWDM. And powerful open optical network automation platforms that exist today, like Infinera’s Transcend, offer the ability and the flexibility to support operators no matter what their IPoDWDM management architecture of choice is.

If you are interested in discussing the IPoDWDM management approaches that best suit your network and organization, we would love to hear from you!