Spring 2018 Optical Connections Magazine


Keeping The Show On The ROADM

By the use of SDN, operators can control a ROADM in terms of end- to-end connectivity, virtualised protection, restoration management and bandwidth management, writes John Williamson

GETTING SMARTER Since the early days of ROADMs, the flexibility of the technology has been progressively extended. Systems have added “Colorless”, “Directionless”, and “Contentionless” capabilities to their repertoires, collectively styled CDC. Colorless enhances the basic ROADM with the ability to connect any channel to any mux port. Directionless enables the sharing of muxes between directions. Contentionless enables multiples of the same wavelength to be added/dropped to the same mux. In their most ambitious iterations, ROADMs add “Flexible-grid” to CDC to become CDC-F ROADMs. Flexible-grid is designed to provide a degree of future- proofing with the ability to dynamically accommodate elevated trac demands. In unison, CDC-F continues the network operators’ ability to make modifications to how the trac is flowing through their networks. “As these modifications are fully implemented at the deployed ROADM nodes and controlled by the network management system, this enables the network to autonomously restore faults within the network, or balance the trac load across the network by routing aected or selected wavelengths dierently within the network,” notes Collings. He adds that CDC-F enables greater universal transceiver sparing and protection approaches, and greater deployment velocity of new wavelengths and services. “These capabilities provide for more eciently used networks with longer growth lifespan, more ecient use of transceiver and electronic switch hardware, and faster revenue capture.” So is the market hurrying to take up CDC-F ROADMs with open arms? Not quite. There might be some way to go. Collings observes that, with modern WSS, transceivers and supporting components, CDC-F systems are reasonably mature. “The current focus of development is on improving the cost and form-factors of these key elements as well as improving the addressable network scale - increasing the number of supported degrees - and scalability - improving the cost/port and the ability ROADM CDCF TAKEUP: MIXED MESSAGES

I n certain optical networking and investors include operators and service providers as diverse as AT&T, China Telecom, South Africa’s FibreCo Telecommunications, the Hong Kong- Americas subsea consortium, Italian operator Open Fiber, Telefónica, Thai operator True, and Verizon. The attractions of these ROADMs are substantial. They oer a compelling alternative to the former need to make physical changes when network and node requirements changed, a process characterised by Jay Gill, Infinera’s Principal Marketing Manager as “operationally extremely complex, cumbersome and costly.” Brandon Collings, CTO of Lumentum, includes among the initial ROADM attractions: flexibility in the wavelength topology to support unpredicted trac growth patterns; the ability to adopt/ deploy wavelength channels with new capabilities and higher capacities; and sectors, Reconfigurable Optical Add-Drop Multiplexers (ROADMs) have been remotely switching trac in Wavelength Division Multiplex systems since the early 2000s. Today, ROADM users

the ability to avoid the high cost of optical regeneration at every node. Overall, early ROADMs could have a very beneficial impact on the way networks were designed. “You didn’t have to pre-plan everything,” notes Gill. “You could make your use of the capacity and spectrum more ecient by using configurability.” There were some shortcomings too. “The initial ROADM networks did not support more than two-degree nodes and therefore did not support optical mesh networking,” states Collings. Again, as Telefónica has reported, its earlier ROADMs improved the reliability and flexibility of services, but also posed challenges for Operation and Maintenance (O&M). Although oset by increased automation within these ROADMs – in areas such as channel power measurement and automatic power balancing – the extra cost and challenges associated with adapting management systems and operational processes to implement the new concept of optical switching undoubtedly deterred some would-be users. “Initially they were viewed as extra cost,” states Gill.

There are dierent approaches to ROADM design and function depending on need.


| ISSUE 12 | Q1 2018


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