PAUL MOMTAHAN OPEN OPTICAL NETWORKING
The concept of multi-vendor, open, and disaggregated optical networking has been around for some time, but only now has it truly come to fruition, writes Paul Momtahan , marketing director at Infinera. 20 YEARS IN THE MAKING OPEN OPTICAL NETWORKS:
I t appears that the stars have now aligned for multi-vendor, open, and disaggregated optical networking. Open application programming interfaces (APIs) with YANG-based data models, compact modular platforms, high-performance coherent transceivers, and multiple standards initiatives have all come together to enable optical networks where coherent transponders/muxponders from one or more vendors can run over an open line system from a different vendor, as shown in Figure 1. Benefits include accelerated innovation, optimized and differentiated networks, and transformed economics. But is this really new? Haven’t we been talking about “alien wavelengths” and “open line systems” for years now? The reality is that
and management aspects of the OTN. It also specifies the frame structures and bit rates used in the network (2.5G, 10G, and 40G) and the mapping of client signals into it. The frame structure made provision for carrying (optional) forward error correction (FEC), while an annex described a first- generation Reed-Solomon (255,239) FEC. G.709 has been revised and amended multiple times since 2001; the current in- force G.709 (2020/06) now includes signal rates at 25, 50, and N x 100G. A network using wavelength-division multiplexing requires a channel assignment scheme so the transceivers know what wavelength they may use and the spectral width of the signal they may transmit to avoid interfering with other users of the network. We do this by specifying a “frequency grid,” so the second important step on the road to open optical networking was the 2002 specification of a fixed-frequency DWDM grid in ITU-T G.694.1. Ten years later, in 2012, a revision added definition for a flexible grid. In 2020, definitions for “frequency slot” and “slot width” for flexible-grid networks were added. An alien wavelength refers to a wavelength generated by a transponder of one vendor or operator transported over the optical line system of a different vendor or operator. It is hard to pin down exactly who first used the term alien wavelength and when. According to Wikipedia, the first mention was in 2009. However, according to Google Scholar, the first reference to an alien wavelength was in a 2004 paper, “OMNInet: A Metropolitan 10 Gb/s DWDM Photonic Switched Network Trial”: “writing signal-ID transparently onto alien wavelengths before they are allowed on the photonic network.”
open optical networking did not happen overnight. The optical industry has been taking incremental steps toward open, multi-vendor optical networks over the last 20+ years. Here are some of the key milestones on that journey. The updating of G.709 in 2001 provided a first step on the road to open optical networks. Originally specified for SDH by the CCITT, the precursor organization to the ITU-T, ITU-T Recommendation G.709 (2001/02), “Interfaces for the Optical Transport Network,” marked the beginning of the Optical Transport Network (OTN) era. It specified how the overhead, sometimes referred to as the “digital wrapper,” provides the functionality to support the operations, administration,
Figure 1: Open optical networking: open Xponders, open line systems, compact modular, and open APIs
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INDUSTRY FOCUS 2021/2022
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