BRANDON COLLINGS ROADM
operators are electing to deploy ROADM networks to support their large capacity networking requirements. Finally, as core WSS technology continues to mature, the cost and size of moderately-featured ROADM networks continues to improve. This is enabling the deployment of ROADM networks further from the metro core and
a node. As a result, next-generation networks are focusing the WSS demand on advanced state-of-the-art integrated WSS components.
SCALING NETWORK CAPACITY IN THE AGE OF SHANNON’S LIMIT The total information carrying
capacity of amplified optical fibre has consistently increased by many orders of magnitude over several decades using DWDM, higher baud rates, and coherent transmission. Unfortunately, today’s technology is approaching a fundamental limit in the total capacity carried within an amplified fibre, known as Shannon’s limit. While advancements will be made, capacity increases are not expected to keep pace with the total network capacity average growth. Therefore, significantly increasing the total network capacity necessitates additional amplified bandwidth, requiring either the activation of multiple fibre pairs along a route or through the utilisation of the C- and L-bands, or both simultaneously. ROADM networks provide a very cost-effective, flexible, scalable, and pay-as-you-grow method to incrementally activate additional fibre pairs simply by installing an additional ROADM node degree. This allows additional capacity to be deployed when and where it is needed and while the network is in service. Similarly, the L-band can be activated within a network when needed and without service interruption by deploying an overlay of L-band ROADM networking elements into each node degree, nominally doubling the network capacity. Additional fibre pairs can also be activated as previously described. Both modes of increasing network capacity result in an increased average number of WSS- enabled ROADM degrees deployed per node. Modern ROADM nodes generally support 16 or more degrees; however, network nodes rarely connect to more than five fibre routes demonstrating the utilisation of capacity growth through multiple fibre pair activation. independent reasons are behind the current expansion of WSS-enabled ROADM network deployments, including the migration from all electrically switch networks, the need for greater optical layer resilience, new operators deploying optical networks, advanced architectures with enhanced flexibility features, and the physical transmission capacity limits of optical fibre. However, as network traffic growth continues unabated, all are fundamentally and sustainably motivated by the same singular underlying need which has historically and consistently motivated ROADM network adoption and deployment: flexible and cost-effective network capacity growth . SUMMARY Many diverse, unrelated, and
into the high-volume metro edge segment of the network where increased capacity,
capability, and flexibility is demanded to support increasing customer bandwidth and the anticipated demands of 5G networks.
Lumentum TrueFlex® Twin 1x20 WSS
Overall, ROADM networks are increasingly being deployed into large geographical regions and into network segments and by emerging operators that have not deployed such networks in the past, creating new demand for WSS hardware. This demand is expected to be robust over time as the fundamental motivation for ROADM network adoption is principally equivalent to the historical drivers, the simultaneous need for capacity scalability and topology flexibility, but with effective cost, size, and power dissipation. ROADM networks have been the dominantly deployed network type for over ten years by many operators in North America, Europe, and Japan. Originally, these networks utilised single WSS devices and inflexible channel multiplexing and demultiplexing structures. As WSS technology has matured, today’s generation of ROADM networks are significantly more functionally capable, enabling full route and operating wavelength flexibility from transceiver to transceiver with colourless, directionless and contentionless (CDC) multiplexing and demultiplexing. This provides the operator the ability to quickly reroute and/or restore any optical link using management software alone without any manual physical intervention. These networks utilise an advanced route and select architecture with two physically integrated WSS devices per degree versus only a single WSS per degree in earlier generations. However, WSS technology innovation allows these advanced features to be adopted at roughly the same physical density and price points as those of earlier generations. Concurrently, the CDC functionality DEPLOYMENT OF NEXT- GENERATION ROADM NETWORKS
and outages. In some networks, such flexibility is provided using full OTN and/or Ethernet electrical switch fabrics at each node alongside manual reconfiguration of physical layer hardware. In these networks, all optical traffic at the node must be converted into the electrical signal domain and routed through an electronic switch fabric. This provides several attractive advantages including the ability to aggregate traffic into higher rate streams and to provide rapid and automated protection and restoration of network traffic. However, every node must contain a full complement of optical transceivers and the electrical switch fabric must be scalable to the maximum capacity growth potential of that node. Many network operators who have historically deployed all electrically switched networks, such as those in China and many developing networks to both reduce the quantity of transceivers and the required scale of the electrical switch fabrics. For the same reason that has historically driven ROADM network adoption, this migration allows these operators to continue to scale their networks, maintain the flexibility they require through balancing the capabilities of the electrically and optically switched network layers, and decrease costs, size, and power dissipation. The criticality and value of optical layer flexibility is also becoming paramount in areas where traffic is both strongly increasing and the deployed fibre infrastructure is prone to a high frequency of fibre cuts, a situation most exemplified within India. Here, operators are deploying next-generation ROADM networks to provide optical layer restoration and avoid additional transceivers and higher electrical switch capacities. Data centre and over-the-top operators are deploying long haul, sub-sea, and even metro networks to interconnect their data centres and more efficiently link to customers and internet peering sites. Much like their traditional national operator contemporaries, this new class of regions, are now migrating to fully featured, next-generation ROADM
is increasingly utilising advanced WSS technology for multiplexing
and demultiplexing rather than fixed wavelength filter arrays, increasing the amount of WSS elements present within
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ISSUE 17 | Q2 2019
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