Although all service providers are interested in IP over DWDM technology, they are not ready to deploy it yet. The debate continued this year at MWC and OFC.

Dr. Oscar Gonzalez de Dios of Telefonica introduced the deployment progress of IP over DWDM in the speech of OFC conference. Although this technology has been commercialized for more than 10 years, it has not been widely adopted in telecommunications networks.

This approach works well for point-to-point links and DCI networks, but telecom networks have a long list of concerns about it. The introduction of the 400ZR/ZR+ module has shortened this list, but there are still two key issues to be resolved:

• Complexity: IP and DWDM transmission require different management teams and software systems;
• Speed: In terms of the data rate of the optical interface, the optical transmission is always ahead of the IP router.

Dr. Oscar Gonzalez de Dios introduced Telefónica‘s progress in the unified control of IP routers and DWDM transmission equipment. He believes that SDN can provide a solution. OIF is advancing projects in this area. Nokia announced its unified IP/DWDM transmission management software at MWC. Ciena also offers multiple layers of management on its routers, as shown in the diagram below.

During OFC, Cisco disclosed that there are now more than 40 service providers who are deploying IP over DWDM, but they are all smaller companies. Simple networks can indeed use IP over DWDM, but complex optical networks operated by large telecom service providers are unlikely to deploy this solution on a large scale.

Google‘s Tad Hofmeister described the successful deployment of the 400ZR on an L3 switch in his network. These deployments are limited to regional (metro) connections in one of the few networks Google runs, but they plan to deploy more this year. Cost savings by not using gray light is helpful, while Google has also deployed SDN to control the entire network, which is a key enabler.

Google plans to deploy 800ZR next, and hopes to have 1.6T pluggable modules in the future. However, if the 1.6T pluggable power consumption is too large, a different solution is required. Distributed routing is one of the options that can be considered, which can accommodate larger line cards and relax the requirements on the size and power consumption of DWDM optical devices.

In April 2023, Ciena launched WaveRouter, which aims to support 1.6T DWDM optical devices per wavelength . This metropolitan area core router can be expanded to a maximum capacity of 192T in multiple chassis, and it is actually a DDC system integrating software and hardware.

One of the challenges in deploying DDC systems is low cost and low power connectivity. Copper or fiber optic cables are currently the main options, and on-board optical modules, such as CXP, have also been used in the past. CPO is expected to play a role in future DDC systems. This effectively brings back into consideration the cost of the gray light modules used to connect the router to the DWDM transmission system.

In the past decade, the cost of gray light modules has dropped significantly. Ten years ago, the price of a 100G CFP LR4 gray optical module was about $5,000. The current 100G LR4 (10 km range), based on QSFP28 package, is priced below $300. Last year, more than one million such optical modules were shipped. Given the scale of production, optical module suppliers can often lower prices to levels unimaginable a decade ago.

The price of 400G FR4 (2 km range) optical transceivers, which shipped a considerable amount last year, will drop below $500 by the end of 2022. It offers a good alternative to the pricier 400G LR4, which has just started shipping.

Network operators attach importance to the flexibility brought by the separation of DWDM transmission and core routers , which is called “IP+DWDM” instead of “IP over DWDM”, IPoWDM and IP+WDM? . This helps manage different data rates. Flexible rate DWDM ports can also be deployed to find the right balance between data rate and distance for a particular network link.

Dr. Maxim Kuschnerov of Huawei discussed this advantage in a PPT of OFC 2023 , as shown in the figure below. This analysis includes not only the cost of the pluggable optical module, but also the cost of its equipment board.

This clearly shows that the cost savings of IP over DWDM is minimal and does not justify the added operational complexity, which is a major problem for large telecom operators . This is one of the reasons why network automation ranks as the number one concern for service providers, the best option to support new applications while reducing network operating costs.

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