Submarine cables form the backbone of the Internet and there are over 300 subsea cables today that interconnect continents and countries. In recent years, as cloud and content providers attempt to reach more users and provide reliable and bandwidth intensive services, submarine infrastructure has exploded. The number of new submarine cables is set to grow by 50 percent in 2019 versus 2018 (source: TeleGeography’s submarine cable map).
All major cloud providers will build out new cables in consortiums or as privately owned cables in the next few years. In a recent Tech Crunch article, Vijay Vusirikala from Google described this as an economic decision related to the sheer scale of bandwidth usage. “It becomes much more cost-effective to build their own cables than it does to rent time on somebody else’s when you reach a certain usage level. This is essentially building infrastructure at scale and with scale getting the optimization benefits,” Vusirikala explained.
Figure1: The below figure from illustrates the strategy of cloud service providers: The objective is to offer better reliability, speed and security performance as compared with the nondeterministic performance of the public internet or other cloud networks.
The other key driver for sub-sea capacity is video. Cisco’s VNI reports between 2017 and 2022, global busy hour Internet use will grow at a CAGR of 37 percent, compared with 30 percent for average Internet traffic. Video is the underlying source of accelerated busy hour traffic growth. Unlike other forms of traffic, which are spread evenly throughout the day (such as web browsing and file sharing), video tends to have a “prime time.” The growing gap between peak and average traffic is amplified further by the changing composition of Internet video. Real-time video such as live video, ambient video, and video calling has a peak-to-average ratio that is higher than on-demand video. This acceleration of video is addressed by the increasing role of Content Delivery Networks (CDNs). CDNs bring content closer to the user and sub-sea cables play a crucial role in connecting content to the CDNs closer to the end user. As per Cisco VNI report, CDNs will carry 72 percent of total Internet traffic by 2022, up from 56 percent in 2017.
How does the Cisco NCS 1004 fit into submarine applications?
The NCS 1004 is the latest product in the DCI form-factor NCS 1000 series. The NCS 1004 delivers multi-haul coherent DWDM transponders that provide state of the art performance for sub-sea applications using granular baud-rate + bits per symbol tuning, time-hybrid modulation, transmit signal shaping and non-linear equalization. Each 2RU form-factor NCS 1004, powered by Acacia’s Pico Digital Signal Processor chip, provides 8 coherent DWDM ports that operate from 100G to 600G.
For current generation uncompensated submarine cables with D+ fiber, 200G-300G is expected to operate over trans-Pacific cables, and 300G-400G is expected to operate over trans-Atlantic cables. While the higher line rate helps lower the cost per bit, time-hybrid modulation allows for continuous control of spectral efficiency which is the key metric to maximizing capacity on expensive submarine cable assets. This short video describes the challenges and intricacies in engineering submarine cable systems.
The clear benefit of the NCS 1004 for submarine cable operators is described in the figure below. Competitor solutions with a limited set of fixed options (usually in nx50G or nx100G line rates) struggle to balance Q-margin and spectral efficiency. In the example below, Option 1 line rate offers enough margin but the spectral efficiency is too low - while a different line rate - Option 2 provides much better spectral efficiency but, not enough Q-margin. With the NCS 1004, the user can adjust each line rate in granular increments to the appropriate point that balances Q-margin and spectral efficiency .
Figure2: The below figure plots Q versus Spectral Efficiency for the NCS 1004 and for a typical competitor product. The NCS 1004 provides a continuous range of spectral efficiency values for different Q. Competitor products offer fixed line rates that limit the ability to maximize spectral efficiency for the desired Q-margin.
Cisco’s NCS 2000 solution complements the NCS 1004 for sub-sea applications with the required Submarine Line Terminating Equipment (SLTE) capabilities. The NCS 2000 portfolio includes amplifiers, ASE noise-loading and intelligent ROADM based colorless add-drop with enhanced monitoring.
Live Field Trial
Cisco was able to demonstrate the benefits of the NCS 1004 over a sub-sea cable in production. The cable we tested ran over 10,000km with accumulated chromatic dispersion of 210,000 ps/nm. This cable was designed as an open cable and had a ROADM line system already deployed with over 20% of the spectrum consumed by 200G channels from a current generation transponder. As part of the trial with the NCS 1004, Cisco tested 200G and 300G over different baud-rates across different parts of the spectrum.
With this test, Cisco’s solution achieved significant milestones. The NCS 1004 drove a single wavelength of 300G over a 10,000km sub-sea link. The spectral efficiency achieved was 43 percent better than any other option available in the industry today. As part of the testing Cisco validated multiple combinations of bits per symbol and baud-rate for 200G line rate that provided granular control of spectral efficiency and Q-margin. This was demonstrated with the NCS 1004 operating as an alien over an existing 3rd party SLTE platform running live traffic.
Cisco and Acacia partnered closely over the last few months to successfully demonstrate the benefits of this new technology in real deployment conditions. We are very proud of these results.
Learn more about Cisco’s latest innovations on our Optical Networking site.
About the Author
Sushin Suresan, Product Manager, Cisco Optical Systems