PAUL MOMTAHAN OPEN OPTICAL NETWORKING
standards-based solutions. The Open Optical & Packet Transport (OOPT) group within TIP, which works on the definition of open technologies, architectures, and interfaces in optical and IP networking, was also formed in 2016, with Facebook contributing the Voyager open packet DWDM transponder platform design. Started in 2017, Gaussian Noise Model in Python (GNPy) within the TIP Open Optical & Packet Transport–Physical Simulation Environment (OOPT–PSE) group defines and develops a common, open source, and vendor-neutral library of algorithms for multi-vendor optical route planning and optimization tools. In 2018, ONF formed the Open Disaggregated Transport Network (ODTN) Project, an operator-led initiative to build DCI using disaggregated optical equipment. Then in March 2020, TIP’s OOPT group published specifications for the Phoenix 400 Gb/s wavelength- capable disaggregated and open optical transponder, with Infinera selected as one of six vendors in July 2020.
multiple vendors, including Infinera.
The first standard for multi-vendor interoperable DWDM interfaces came in 2005. A key motivation for open optical networking is that it enables operators to source network components frommultiple vendors. One aspect of this is multi-vendor interface interoperability, which the ITU-T SG15 refers to as “transverse compatibility.” To enable this, the ITU-T specifies a “black link” approach with “application codes” (AC) for transceivers, the idea being that regardless of origin, two devices bearing the same AC are guaranteed to interoperate when connected over an optical channel that also conforms to the AC specification. The 2005 ITU-T G.698.1 recommendation specifies ACs for 2.5 Gb/s and 10 Gb/s wavelength signals in unamplified point-to-point DWDM systems using a 100 GHz grid, enabling reaches in the 30 to 80 km range. A 2006 revision of the recommendation allowed for the inclusion of OADMs in the link and provided a means to calculate the number that could be accommodated. In contrast to G.698.1, which dealt only with unamplified links, G.698.2 specifies ACs for systems containing amplifiers. Beginning with 2.5G and 10G NRZ modulation, G.698.2 now covers coherent 100G applications with third-generation FECs as specified in G709.2 and G.709.3. The IETF first published Network Configuration Protocol (NETCONF), a key enabler for open APIs, as an RFC (RFC 4741) in 2006. It then updated NETCONF with RFC 6421 in 2011. First appearing as an internet draft in 2013, RESTCONF provides a subset of NETCONF functionality implemented on top of HTTP/ HTTPS. It became an IETF standard (RFC 8040) in 2017. The YANG data modeling language can be used to write network element configuration and state data models for protocols such as NETCONF and RESTCONF, and as such is also a key enabler for software-defined networking (SDN) and open APIs. The IETF published YANG 1.0 (RFC 6020) in 2010, followed by YANG 1.1 (RFC 7950) in 2016. Having first defined the requirements for transport SDN in 2013, the Optical Internetworking Forum (OIF) then published a transport SDN framework in 2015 that compared the then-emerging SDN architecture with established ASON control planes and identified candidate open interfaces for SDN control of optical networks. In 2014, the Open Networking Foundation (ONF) launched the Transport API (TAPI) project to create a standard for the northbound interface from a transport SDN controller. In 2016, TAPI 1.0 was published in partnership with OIF, its release being timed to align with a 2016 joint OIF/ONF interoperability demonstration. In 2017, ONF, OIF, and the Metro Ethernet Forum (MEF) jointly released TAPI 2.0, followed by TAPI 2.1 in 2018. In 2020, TAPI 2.1.3 interoperability testing concluded, with participation by
In September 2014, Infinera launched Cloud Xpress, the industry’s first muxponder appliance, delivering 500 Gb/s of line-side capacity and 500 Gb/s of client capacity in 2RU. This was a key enabler for optical network disaggregation in data center interconnect (DCI) applications. In 2016, Coriant, which was acquired by Infinera in 2018, evolved Infinera’s original transponder appliance concept with a compact 1RU device with four slots for sleds, the Groove G30, creating a new category for optical equipment – compact modular. OpenConfig, an informal working group of network operators, was formed in 2015 with the goal of moving networks toward a more dynamic, programmable infrastructure, using SDN principles, with a focus on common data models and streaming telemetry. Also in 2015, Google Remote Procedure Call (gRPC) was initially developed by Google and is currently an internet draft. gRPC provides a very fast and efficient method of transmitting data. gRPC Network Management Interface (gNMI) is a gRPC-based management protocol for streaming telemetry and configuration management. An open line system is an optical line system (mux/demux filters, wavelength selective switch, amplifiers, etc.) that can support wavelengths generated from third-party devices, with some definitions making open, SDN-based management a mandatory requirement. As with the term alien wavelength, the exact date this term entered the lexicon is hard to pin down. However, Google Scholar gives a first reference to the paper “SDN Control of a Coherent Open Line System” by Microsoft in 2015. The Open ROADMMSA was formed in 2016 with the aim of producing specifications for multi-vendor-interoperable ROADM networks. The MSA publishes optical specifications for data-plane interoperability, including transponders, OTN switches, and pluggables and associated open APIs and YANG data models. The first specifications were for a 100 Gb/s G.698.2-compliant transponder and a colorless-directionless fixed-grid ROADM. In 2017, OTN Xponder/ switch, inline amplifiers, and flexible grid were added. In 2018, additional signal rates (200 Gb/s, 300 Gb/s, and 400 Gb/s) were added together with OTUCn and FlexO. In 2019, ODUflex, 400G clients, low- noise amplifiers, streaming telemetry, and bookended transponders were all added to the specifications. Open ROADM was the first organization to adopt the appropriately named Open FEC (OFEC) as the FEC for line rates beyond 100G. Telecom Infra Project (TIP) was founded by Facebook, also in 2016, as a diverse community working together to develop, test, and deploy open, disaggregated, and
Figure 2: The 20-year journey toward open optical networks
So, to summarize, while no one thing was sufficient by itself to enable open optical networking, the cumulative effect of these many initiatives over the last 20 years, as shown in Figure 2, has brought us to a place where open optical networking is now a practical reality.
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