What Are The Main Benefits of Next Generation ROADM?

Since their early 2000s introduction, ROADMs have evolved through three generations: wavelength blockers, two-degree planar lightwave circuits, and multi-degree WSS. WSS-based ROADMs are now globally deployed, offering simplified planning and better bandwidth utilization. However, they face limitations like fixed wavelength and direction assignments and partitioned add/drop structures. The ROADM market is now shifting to the fourth generation, introducing colorless, directionless, contentionless, and flexible spectrum functions, with a focus on automating optical connection endpoints. This post will introduce the main benefits of next generation ROADM.

Features of Next Generation ROADM

Next generation ROADMs (NG ROADMs) consist of four primary functions: colorless, directionless, contentionless, and flexible spectrum/flex grid, collectively known as CDC-F. These functions can be deployed together or in various combinations like CD, CDC, or CDC-F. Here’s a brief overview of each function:

Colorless: Traditional ROADMs have fixed add/drop transceiver and wavelength assignments, requiring manual connection to the correct port. Colorless ROADMs automate this process, allowing any wavelength to be assigned to any port via software control and tunable transponders , eliminating the need for on-site technicians.

Directionless: Existing ROADMs are direction-dependent, fixing add/drop port pairs to specific directions. Directionless ROADMs enable any wavelength to be routed to any direction served by the node through software control, removing the need for physical rewiring.

Contentionless: The industry has long discussed colorless and directionless ROADMs, but contentionless ROADMs are a newer concept. Despite colorless and directionless functionalities, networks can still face limitations requiring manual intervention due to wavelength blocking. This occurs when two wavelengths of the same color converge at the same WSS structure, causing contention. Operators must partition add/drop structures to prevent such conflicts, sacrificing dynamic flexibility. Contentionless ROADMs solve this by allowing multiple copies of the same wavelength on a single add/drop structure without partitioning. Combining colorless, directionless, and contentionless functionalities (CDC) provides ultimate optical layer flexibility, which is the goal for operators planning ROADM networks.

Flexible ITU Grid or Flex Spectrum: A key concept in NG ROADM architectures is flexible spectrum, also known as "gridless" or "flexible grid." This feature helps future-proof networks for speeds beyond 100G, like 400G or 1 Tbit/s, which require more than 50 GHz of spectrum. The solution is a granular ITU grid with 12.5 GHz increments, allowing ROADM nodes to operate at various speeds based on these increments, such as 75 GHz or 125 GHz spacing.

Benefits of Next Generation ROADM

Opex and Capex Reduction

Opex reductions primarily come from automating network bandwidth activation, particularly by automating endpoint activation of photonic layer circuits. Traditional ROADM systems allowed touchless provisioning at intermediate sites but required technicians on-site at entry and exit locations of circuits. CDC functionality removes the need for technician visits, saving on labor costs and provisioning time. Automation also reduces manual errors and connector issues.

On the capex side, operators benefit from increased fiber utilization, reducing the need for additional equipment purchases. BT has researched using flex spectrum to maximize fiber use. Combining ROADMs with OTN switching further enhances fiber utilization and capex savings compared to using ROADMs alone. OTN provides efficient grooming for sub-wavelength traffic, ensuring optimal wavelength utilization before switching at the ROADM layer. Centralized OTN switch fabrics improve grooming efficiency over OTN muxponder-based systems by handling traffic across line cards.

Integrating large-scale OTN switching and ROADMs in a single system eliminates costs associated with connecting separate DWDM and OTN switching boxes, optimizing the architecture and reducing overall costs.

Rapid Bandwidth/Capacity Provisioning

Automating bandwidth and capacity provisioning not only reduces operational expenses by eliminating human intervention but also significantly speeds up the process. Operators consider the ability to quickly respond to capacity demands as a crucial competitive advantage in the highly competitive telecom industry. Rapid deployment of capacity and services is also essential for effective cloud service delivery.

The revenue generation and service differentiation benefits of Next-Generation Reconfigurable Optical Add-Drop Multiplexers (NG ROADMs) should not be underestimated. According to past surveys by Heavy Reading, these benefits have been rated as highly impactful in some cases, comparable to savings in operational and capital expenses (opex/capex).

Moreover, recent trends show that optical initiatives closely aligned with revenue enhancement objectives are gaining higher priority within organizations faster than traditional opex/capex savings strategies.

Topology Flexibility and Simplified Operations

CDC-F ROADMs are characterized by enhanced flexibility, offering reconfigurability not only at intermediate nodes along an optical route but also at endpoints. Historically, to change traffic direction, technicians had to physically disconnect and reconnect individual connectors between WSS elements (e.g., East to North or South). By automating these endpoint connections, CDC ROADMs significantly enhance network flexibility at the photonic layer and simplify operations, contributing to opex savings.

Flex spectrum introduces another layer of flexibility at the photonic layer. Flex-spectrum ROADMs support current 10G, 40G, and 100G wavelengths on a 50GHz fixed grid but are also designed to accommodate future technologies like 400G and beyond, regardless of bit rate or channel spacing.

Without flex-spectrum ROADMs, operators would need to deploy entirely new networks for 400G and higher bit rates while maintaining legacy fixed-grid systems for 10G, 40G, and 100G traffic.

FS ROADM Introduction

FS D7000 series ROADM-09T is based on advanced next-generation wavelength-selective switch (WSS) technology to support full colorless, directionless, and contentionless (CDC-F) system configuration. This module is a built-in pre-amplifier and booster amplifier which can simplify the installation and scalability of your ROADM network while improving its overall flexibility and performance. ROADM-09T supports N*12.5GHz flexible grid (4≤N≤12). Besides, this module can achieve add-and-drop services or pass-through.

Conclusion

In conclusion, the evolution to Next-Generation ROADM (NG ROADM) technology represents a pivotal advancement in optical networking, promising unprecedented flexibility and efficiency. By integrating colorless, directionless, contentionless, and flexible spectrum functionalities, NG ROADMs not only streamline operations and reduce costs but also pave the way for future-proof networks capable of meeting escalating bandwidth demands. These innovations not only enhance network agility and scalability but also position operators to deliver services more rapidly and effectively, driving competitive advantages in the dynamic telecommunications landscape. As organizations prioritize revenue enhancement alongside traditional cost-saving strategies, NG ROADMs emerge as a cornerstone of modern optical infrastructure.