In part one of this two-part blog series, we discussed how to Reduce stress with the right OLS. That is, how to overcome fiber capacity exhaust, a constrained network bandwidth management environment, and stresses on your critical network by selecting scalable, flexible, and resilient application-optimized optical line systems (OLS).

In part two, let’s focus on a common situation where your network fiber capacity is maxed out on many, but not all, of the C-band WDM channels in the existing fiber plant. Historically, as seen in Figure 1, carriers increased network capacity by (1) employing advanced Raman amplification to improve spectral efficiency or (2) leveraging advanced coherent optics with higher data and baud rates to add faster channels. Both options are now constrained as the latest advances approach the Shannon Limit of fiber capacity. Of course, another option is to lease an additional fiber pair but most operators find this cost-prohibitive.

Figure 1. Options for scaling capacity of existing fiber

This dilemma has accelerated the broad adoption of (3) C+L-band network upgrades. By utilizing the L-band, in addition to the traditional C-band, you can double your fiber capacity and maximize the return on investment (ROI) on that fixed-cost leased fiber.

A key challenge is a prolonged overlay build that strands assets in the existing ROADM and inline amplifier (ILA) sites. Typically, the network isn’t congested in all links. Traffic growth may lead to capacity exhaust in some links but not yet in others. In this case, a massive overlay build may not be warranted. Moreover, given the traditionally long CAPEX lifespan of a line system, it’s likely these sites use equipment from a prior generation that share similar degree density, add/drop configuration, or functional integration.

In all cases, a hitless upgrade is paramount. Your customers and your revenue stream can’t afford mission-critical service disruptions.

So how can operators address the challenge of upgrading network capacity into the L-band selectively, seamlessly, and cost-effectively? Is there a solution that allows you to upgrade congested critical links and upgrade others as needed without impacting traffic?

Thankfully the solution exists.  With Nokia’s modular C+L optical line system, you can seamlessly enable link and network-level scalability as needed with maximum flexibility. It enables you to scale your critical network selectively by adding L-band capacity link by link and node by node, across an entire region or network. Link-level scaling doesn’t require you to uniformly upgrade all links. The ultimate network-level scaling option lets you pay as your network traffic grows.

Both approaches result in cost benefits of hitless, in-service link-level upgrades while optimizing CAPEX. Network-level C+L scaling doubles the entire sub-network or entire network fiber capacity, avoiding the cost of leasing additional fiber pairs.

Now let’s explore several of the scenarios where an upgrade to C+L band capacity is needed, and how Nokia enables a seamless upgrade solution.

One common use case is where varying, dynamic traffic growth across the network is congesting some links before others, creating capacity constraints in some portions of the existing, or brownfield, C-band-only sub-network.

In this case, the first step to expanding network capacity with C+L is to upgrade the most congested links to C+L-band, by adding L-band amplification and ASE noise loading to double capacity on selected links without impacting pre-existing C-band-only connections. The automated self-tuning capability in Nokia line systems eliminates the impacts of SRS tilt across the entire C- and L-bands.

As a next step, additional links serving traffic connections that transit through the upgraded C+L ROADM nodes can also be upgraded to C+L by deploying L-band equipment.  This enables new L-band transparent end-to-end connections across upgraded links without interruptions to connections on existing links.

This process can be repeated in multiple subsequent steps, to enable a network-wide C+L upgrade that doubles total available fiber capacity and provides more spectrum to support a large number of end-to-end lightpaths across many nodes.

Another use case involves upgrading nodes with different generations of ROADMs.  In this case, Nokia’s modular C+L upgrade provides a solution to migrate ROADMs of any generation to the desired functionality, with C+L capability.

The Nokia solution lets you progressively upgrade nodes that utilize previous generations of Nokia C-band line system technology to new C+L-band systems, using C+L-band couplers, L-band amps, and ASE noise loading to enable hitless upgrades.

For example, a network operator may seek to upgrade an existing 2^nd generation C-band only CDC-F ROADM node to 3^rd generation C+L ROADM.  This can be progressively done by installing the L-band equipment, with only the traffic in the upgraded link being interrupted during the upgrade, while add/drop and transit traffic not traversing the upgraded link is not impacted.

Similarly, a network operator can upgrade an existing 2^nd generation C+L-band ROADM node, supporting either C-F or CDC-F functionality, to a 3^rd generation C+L C-F or CDC-F ROADM, by upgrading to the latest ROADM technology in each direction without impacting traffic on the other ROADM degrees.

Finally, an operator can upgrade an existing 3^rd generation C-band ROADM to a C+L ROADM by Simply connecting new L-band ROADMs to the L-band fiber shuffles, without impacting any of the existing traffic, or link.  In all these cases, network operators can benefit from the additional capacity enabled by upgrades to C+L band, while also protecting their installed base investment and maximizing the ROI of embedded equipment.

Level up without downtime

C+L-band upgrades can double network capacity and help maximize ROI on leased fiber pairs. To optimize CAPEX and minimize service disruptions, consider modular C+L upgrade solutions that allow you to:

• Selectively and seamlessly upgrade only congested network links and nodes

• Progressively upgrade nodes with varying ROADM technology generations.

Network operators worldwide have deployed our C+L optical line systems. Let us help you level up your network capacity with no network downtime.

Visit our webpage and read our eBook for more information!