Open Cables: From Close to Open Cable Systems
By Vincent Gatineau and Geoff Bennett
May 28, 2021
There are over 400 submarine communication cables deployed under the seas and oceans of the world today. With a typical cable having an engineering design life of at least 25 years, it’s not surprising that a given cable will have the opportunity to use several generations of transponder technology over its lifetime.
Or will it? Figure 1 shows the building blocks of a submarine cable system, showing the breakdown of the wet plant (cable, amps, branching units) and the dry plant (high- voltage management, wave mux/demux – usually a ROADM today, wet plant monitoring, optical power management, and transponders). When submarine cables were first deployed, it was common practice to have a single prime contractor for the entire system, including the transponders, and contractual language would typically restrict the cable operator to buying the transponder technology from that prime contractor.
For many years this was simply accepted as “the way we do things” in the submarine communications world, but that began to change around the year 2009 when terrestrial transponder vendors showed that their equipment would work just fine over existing, dispersion-managed submarine cables (see sidebar), and that they could offer those transponders at lower prices and with shorter lead times than the legacy suppliers. That was still the era of 10 Gb/s per wavelength, non-coherent transmission, but the trend really began to accelerate when coherent transponders demonstrated a 4X to 10X increase in wavelength data rates (to 40 Gb/s or 100 Gb/s per wavelength), and a similar factor increase in fiber capacity.
Only a small number of optical equipment vendors were able to invest in coherent technology, and this period (around 2012) also saw a dramatic rise in the importance of the hyperscale internet content providers (ICPs) as not only consumers of submarine network capacity but also active participants in cable consortia. ICPs were already leading the charge toward disaggregated, open standard solutions within the data center as well as over their terrestrial networks between data centers. They began to consider the submarine network link as an extension of that open network architecture, and part of that vision was for submarine cables to be “open” – with no obligations (neither technical nor commercial) to use a given transponder type. At that stage there was gradual and, in some cases, reluctant participation by wet plant vendors toward this process, but eventually it became more practical for third-party wet plant monitoring equipment to operate with most of the legacy wet plant deployed. Thanks to a general acceptance of the value of open cables, new cable systems from 2012 onward were almost all designed from scratch to be open, and with commercial terms that allowed a flexible choice of transponders.