The Open Optical Networking Blogs, part 3
In this blog series, Fujitsu’s Francois Moore explores the key issues and current developments in open optical networking. The topics addressed include Adding Alien Wavelengths, Controlling Multi-Vendor Optical Networks, Opening the ROADM network, Disaggregating the Transponder, and Planning with Multi-Vendor Optical Design Tools.
The first two blogs of this series describe an approach to open optical networks commonly referred to as partial disaggregation. It focuses on deploying a multi-vendor SDN controller as well as bookended transponders over a closed, proprietary ROADM network. This approach provides some of the benefits of a disaggregated network while avoiding many of the complex interoperability issues encountered when increasing the openness of the network architecture.
The Next Level: Open ROADM
The Open ROADM initiative started in 2016 with the goal of allowing service providers to open their network by allowing multiple vendors to coexist within the same domain. This initiative pushes the open optical initiative to the “next level” compared to the approaches discussed in previous blogs in this series.
Open ROADM adds the following two important capabilities:
- Transponders do not have to be bookended. The Open ROADM architecture provides the ability to use transponders from different vendors at each end of the circuit.
- ROADMs do not have to be sourced from a single vendor. The ROADM network can be deployed using different vendors coexisting within the same network.
This high degree of choice and flexibility requires a strong commitment to multi-vendor interoperability based on the Open ROADM Multi Source Agreement (MSA) specifications.
Open ROADM Multi Source Agreement (MSA)
The Open ROADM MSA provides the technical foundation to deploy networks with a complete amount of flexibility as depicted in the reference diagram below. Each color represents a different vendor and as we can see, there is a complete mix and match of vendors interoperating with each other. The only restriction is that the transponder or ROADM must be compliant to the Open ROADM MSA specifications.
Figure 1: Reference model for Open ROADM
The MSA specifies ROADM and transponder optical parameters at the fiber span (multi-wave) and wavelength (single-wave) levels, including launch power levels, per channel power levels, PMD tolerance, line rate, baud rate, FEC algorithm, alarming, performance monitoring, OTDR specifications, and much more. Vendors must comply with these requirements in order to allow a completely disaggregated optical network. The requirements are prescriptive and very detailed in order to ensure that compliant products will successfully interoperate.
The Open ROADM MSA also defines its own YANG data models to represent both the ROADM and the transponders. The multi-vendor SDN controller manages these network elements using the standard NETCONF protocol. This data model and management API performs a similar function to the T-API and OpenConfig components discussed in my previous blog.
The definition of a standardized Open ROADM data model allows carriers to deploy and operate the network via a single multi-vendor SDN controller. The Open ROADM data model becomes the universal language used by every node within the network as well as by the SDN controller.
Value for the Service Provider
The Open ROADM architecture allows complete flexibility in the selection of vendors. A single vendor can deploy the initial ROADM network, but new vendors can be added to the network at any time, as long as all of the equipment is MSA-compliant.
Similarly, for transponders, different vendors can be used at each end of the wavelength. This flexibility can prove invaluable when inventory and lead-time issues arise, as the ability to mix and match helps eliminate delays.
In addition, a single data model minimizes the development and integration effort required for the SDN controller to support new network equipment. It is contingent upon the new ROADM or transponder vendor to comply with the pre-defined Open ROADM model.
With greater interoperability and more competition between vendors, the benefits for the service provider are numerous: best-of-breed technology, supply chain resilience, easier multi-source management, reduction in logistics and deployment planning, and elimination of pitfalls, which typically lead to service activation delays.
Learnings from the Open ROADM MSA
These benefits do not come without challenges, many of which are similar to those encountered in other open networking initiatives. The extensive Open ROADM MSA enables a high level of choice and flexibility, but this also requires plenty of coordination, specification and up-front agreement between the participants.
Active participants, like Fujitsu, built up institutional knowledge about how to jointly develop functionality in a multi-vendor environment. For example, we learned the importance of thorough documentation that left little for interpretation. Participants learned to document implementation decisions, as well as the intent behind them, so that others better understood the goal. This documentation also helped avoid finger pointing later on, so that conflicts could be resolved more quickly.
Much effort has been spent ensuring that Open ROADM vendors’ products are MSA-compliant and interoperable with each other. It must be stressed that interoperability testing between vendors is absolutely critical to the success of any multi-vendor initiative. As a result, integration with the multi-vendor SDN controller is much faster due to the existence of a standard, vendor-neutral Open ROADM data model.
Tier 1 Service Provider Open ROADM MSA Deployment
Fujitsu is a founding member and active contributor to the Open ROADM MSA. The open optical architecture of the MSA has been approved and is currently being deployed by a Tier 1 service provider in North America. The software control and optical interoperability of their metro ROADM network deployments is depicted in figure 2.
Figure 2: Open ROADM deployment at a Tier 1 service provider
The service provider chose the Fujitsu Virtuora PD planning and design application to optimize and simplify planning, design, configuration and testing of their open optical network. For centralized SDN control, the lone multi-vendor controller selected is the Fujitsu Virtuora Network Controller (NC). The controller supports a NETCONF/YANG interface for the ROADM nodes and transponders in the network. The Layer 0-1 physical hardware includes the Fujitsu 1FINITY L100 and 1FINITY L110 ROADM elements and 1FINITY T300 transponders interoperating with MSA-compliant ROADM and transponders from other vendors. This system is running applications at 100G over a DWDM optical network, with 400G data rates coming in 2021. Other network elements approved for use in this network include the 1FINITY C200 series Communications Integrator for multi-blade control and the 1FINITY Housing frame for power distribution.
Having proven the use of these software-controlled ROADMs in production customer traffic, this service provider is now moving toward scaling Open ROADM deployments across all metro ROADMs. As a key contributor to the Open ROADM MSA and this network deployment, Fujitsu has taken a leadership position in providing seamless multivendor interoperability that introduces efficiencies to the transport network and lowers operating costs.
Disaggregation: Opening up the transponder
Open ROADM focuses on disaggregating the network by allowing the coexistence of multiple ROADM and transponder vendors with very few restrictions. My next blog will focus on a different direction in terms of disaggregation. So far, the transponder remains a complete system – hardware plus software – from a single vendor. Such was the state of routers several years ago. Due to virtualization, new router architectures and products have since appeared where the software is disaggregated from the hardware, and the data plane separated from the control plane. The same trend is now happening in the optical networking world with disaggregated transponders,