Optical network operators face growing challenges as they expand and adapt their WDM networks to support evolving topologies. These challenges include simplifying wavelength deployment, minimizing operational expenses (OPEX), and ensuring the network remains both scalable and cost-effective.
A ROADM is an all-optical network element that enables dynamic software-driven provisioning of wavelengths in DWDM network services from a remote management system without major network changes or redesign.
Flexible wavelength routing in ring and mesh DWDM networks enable simple and fast turn-up of new services without redesign or major changes to the network.
Network topologies are shifting from simple point-to-point configurations to more complex ring and mesh architectures, and operators are tasked with introducing new wavelengths, reconfiguring existing paths, and efficiently managing the allocation and performance of these wavelengths. As bandwidth demands rise, WDM solutions must be able to support as many 96 wavelengths, where each one may follow a different route.
Reconfigurable optical add-drop multiplexers (ROADMs) play a pivotal role in this process, as they enable dynamic, software-driven provisioning of wavelengths, without requiring major network redesigns or physical changes. In ring and mesh DWDM networks, flexible wavelength routing allows for the rapid deployment of new services with minimal disruption.
The ROADM allows automatic balancing of the wavelengths’ optical power across the network, critical especially in links with many EDFAs and multiple channels, where certain wavelengths/services may suffer and introduce errors if the power is not balanced.
The ROADM Building Blocks
PacketLight’s ROADM device includes EDFAs and DCM in a highly integrated 1U footprint, saving space and power consumption. Components include:
- Wavelength selective switch (WSS) – an active component that performs the actual wavelength switching. The WSS enables the user to dynamically route any wavelength to and from any port and then seamlessly change connectivity as needed.
- Optical channel monitoring (OCM) – monitors the optical power of each wavelength.
- Variable optic attenuators (VOAs) – configures the attenuation of optical power in each wavelength
OCM and VOA enable monitoring and dynamic optical power balancing of all channels across the network, critical in links with multiple channels and Erbium-doped fiber amplifiers (EDFAs). Without proper power balancing, some wavelengths or services can degrade, leading to errors and reduced performance.
Figure 1 shows the structure of a typical ROADM device with eight input ports.
Figure 1: Diagram of 8-degree ROADM
With its industry-leading 1U footprint and WSS switching speed, PacketLight’s ROADM is ideal for wavelength routing in core metro and edge networks.
ROADM Network Architecture
The ROADM node comprises several ROADM devices connected to each other using their input ports. Each RODAM device is connected to a different ROADM switching direction, called degree.
ROADM Nodes in Ring Networks
Figure 2 shows a four-degree ROADM node in a ring with East and West facing ROADM devices. The WSS can route any color towards the drop side of the node or bypass it to the next node. The input port can receive the whole C-band and selectively add/drop, bypass or block any channel selected.
When combining tunable transceivers, the ROADM becomes the most flexible and easily scalable solution for optical networks.
Figure 2: Diagram of Four-degree ROADM Ring Network
This architecture adds an additional level of flexibility, allowing wavelengths to route or drop from any line to any line. In an event of failure of any of the services, the protecting wavelength routes its path through the network to overcome or bypass the failure.
ROADM Nodes in Mesh Networks
Two-degree ROADM nodes can be used in simple ring topologies. For more complex mesh network architecture higher degree ROADM nodes are required, as illustrated in Figure 3 below.
Figure 3: Diagram of ROADM Nodes in Mesh Network
The number of node degrees depends on the number of WSS components present in the node, as the multi-degree node is formed by connecting several WSS. As an example, Figure 3 shows a 3-degree ROADM node, where 3 ROADM devices each face a different fiber and connect to the other fibers and the add/drop port.
Automatic Channel Restoration
PacketLight ROADM solution supports automatic channel restoration, which provides protection for optical channel services.
When two ports are selected as the source for the same channel, that channel is automatically protected by the channel restoration mechanism, so that if a channel LOS is detected on one of the ports, the WSS automatically adds that channel from the second port.
Figure 4: Diagram of site using ROADM restoration
A-Z Wavelength Provisioning Using NMS
One of the main advantages of ROADM networks is the capability for remote provisioning. PacketLight LightWatch© NMS provides A-Z provisioning of wavelengths across the network. LightWatch automatically discovers the network topology, finds the optical path between the nodes, determines the relevant configuration for all ROADMs in the path, and performs the provisioning for the required wavelength. The whole process is done remotely using a network management system.
Figure 5: PacketLight LightWatch Wizard for A-Z Provisioning
The NMS also enables to easily route wavelengths from any site to any site without remotely, and allows the network administrator to select the path and assign a protection path.