ROADM Network

PacketLight’s reconfigurable optical add/drop multiplexer (ROADM) saves space and power consumption, provides easy scalability, and a high level of integrated optical elements such as EDFAs and DCM in a single 1U box.

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.

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.

As bandwidth requirements grow rapidly, WDM solutions have scaled up from typically 8-16 wavelengths to 48-96, with different routes per each wavelength and mesh connectivity between sites. Today optical network operators are challenged with extending and modifying their WDM networks by adding new wavelengths and changing the wavelength path within the network. Network managers are also required to keep track of the allocated wavelengths, monitor their operation and deploy new wavelengths easily while reducing the network OPEX.

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The ROADM allows automatic balancing of the wavelengths’ optical power across the network. This is a critical task especially for links with many EDFAs and multiple channels, where certain wavelengths/services may suffer and introduce errors if the power is not balanced.

The ROADM Components

ROADM Components include:

  1. 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.
  2. Optical channel monitoring (OCM) - monitors the optical power of each wavelength.
  3. Variable optic attenuators (VOAs) - configures the attenuation of optical power in each wavelength

The last two components allow monitoring and dynamic balancing of optical power for all channels across the network.

Figure 1 shows the structure of a typical ROADM device with four input ports (P1 to P4).

Diagram of ROADM Device with Four Input Ports
Figure 1: Diagram of ROADM Device with Four Input Ports

With its industry-leading 1U footprint and WSS switching speed, PacketLight’s ROADM is the ideal wavelength routing solution for core metro and edge networks.

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 two-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.

Diagram of ROADM Ring DWDM Network, Two-degree Node
Figure 2: Diagram of ROADM Ring DWDM Network, Two-degree Node

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.

Diagram of ROADM Nodes in Mesh Network Architecture
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.

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.

PacketLight NMS LightWatch

Figure 4: PacketLight LightWatch Wizard for A-Z Provisioning

The NMS also enables to easily route wavelengths or group of wavelengths from any site to any site without remotely, and allows the network administrator to select the path and assign a protection path.

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