1. Introduction

The Open ROADM Multi-Source Agreement (MSA) is a set of published interoperability specifications that lets Reconfigurable Optical Add-Drop Multiplexers (ROADMs), transponders, in-line amplifiers, and pluggable optics from different vendors operate as one network under a single Software-Defined Networking (SDN) controller. It does this with two coupled deliverables: optical interoperability specifications that fix the transmit and receive behavior at defined interface points, and open YANG data models that fix how a controller configures, monitors, and provisions each device over the Network Configuration Protocol (NETCONF). AT&T initiated the work in 2015, the group validated its first specifications at a plugfest in February 2016, and the MSA launched publicly at the Optical Fiber Communication Conference (OFC) that spring; trade coverage of the founding period names Ciena, Fujitsu, Nokia, and Orange among the earliest members alongside AT&T. As of 2026 the effort remains active, with model release 19.0.0 published in May 2026 and optical specification v9.0.0 published in November 2025, both recorded in the MSA's public repository.

The problem the MSA addresses is structural rather than cosmetic. A traditional DWDM deployment welded the transponder, the line system, and the management software into one vendor's closed appliance, so a second supplier's wavelength could not enter the same fiber and a second supplier's controller could not touch the same node. The Open ROADM answer partitions the network into three interchangeable device classes with fully specified boundaries, then abstracts every class behind a common NETCONF and YANG interface, so procurement, capacity growth, and software control each decouple from any single vendor's release schedule. That partition is the same architectural move that produced open line systems across the wider industry, and Open ROADM remains the most complete published version of it because it standardizes the device models and the optics together.

This reference covers the MSA end to end at working-engineer depth: the release structure and 2026 status, the device classes and their W, Wr, MW, MWi, and OSC interface points, the device, network, and service YANG models with their logical connection points, the interoperable W-port modes and their FEC parameters, the flexible-grid and OSNR arithmetic a planner runs against them, commissioning and TransportPCE provisioning sequences, performance monitoring, troubleshooting, and a comparison against OpenConfig, the Open Networking Foundation (ONF) Transport API (TAPI), and OpenZR+. Every figure in the text carries its evidence class, standard-specified, measured, vendor claim, or derived, in the sentence where it appears.

2. Multi-Source Agreement Structure and Release History

The MSA publishes three interlocking artifact families, and knowing which family governs a question saves hours of misdirected reading. The optical and digital specifications, distributed as a versioned workbook on openroadm.org and the public repository, define transmit and receive parameters, alarm and performance-monitoring behavior, supervisory-channel behavior, and laser-safety shutoff at each interface point; v9.0.0 of this workbook was published in November 2025 (repository record). The YANG model set, versioned separately, carries the device model, the network model, and the service model that controllers compile against; releases 18.0.0, 18.1.0, and 19.0.0 landed in November 2025, January 2026, and May 2026 respectively (repository record). White papers for the device, network, and service models, most recently issued for the 13.1 model generation, explain intent and worked controller sequences that the raw YANG cannot.

Release cadence has held near one model release per quarter, ten releases between 14.1 in January 2024 and 19.0.0 in May 2026 in a major-then-minor pattern (15.0 followed by 15.1, 16.0 by 16.1), and Figure 1 places both release tracks, model and optical specification, on one time axis (repository record). Backward compatibility is handled operationally rather than by freezing the models: at OFC 2025 the member demonstration ran ROADM, muxponder, OTN switch, transponder, and regenerator equipment spanning model versions 2.2.1, 7.1, and 12.0 in one interoperable network reaching 1.2 Tb/s, which included the first multi-vendor 800G pluggable ROADM link (demonstrated). A production controller therefore needs to mount and manage several model generations at once, and Section 7 returns to the design consequences.