The Open Submarine Cable Model

In the earliest fibre optic cable systems there were no optical amplifiers, but rather repeaters which converted the optical signal to a digital representation which the repeater laser translated back into a fresh new optical signal. In other words, these repeaters had small computers which converted the laser signal into zeros and ones and put them into the laser's buffer.  The repeater had a fixed transmission rate and generally it was necessary to buy the repeaters and optical cable landing station equipment from the same vendor to ensure interoperability. So undersea repeaters were not technology agnostic; moreover,  they had a fixed transmission rate that effectively made upgrading  a subsea cable to higher throughput impossible. Finally, the need to buy both wet and dry plant from the same vendor limited price competition. This is a severe disadvantage when each new generation of optical technology is reaching the market at approximately 18 months intervals. Furthermore, the first fibre optic cables were put into service in the early 90s at the beginning of the Internet era with an unanticipated tsunami of private and public data traffic swamping telecommunication networks. The first fibre optic subsea cable, TAT-8, maxed out in slightly over 18 months. Because it used optical repeaters  as opposed to technology agnostic optical amplifiers, it could not be upgraded. Not a very good return on investment. 😀

Optical amplifiers changed everything because they were technology agnostic. These pure optical amplifiers absorb a photon and emit a new one with exactly the same characteristics in terms of wavelength and phase. The amplifier contains erbium doped glass. Pumping lasers push the erbium ions into higher energy states. When a photon hits the ion molecule, it is absorbed and a copy cat photon with the same wavelength and phase is emittted. So no digital processing is required.  Not O-E-O conversions. This reduces latency, equipment complexity and dramatically improves bandwidth scalability. 

Optical amplifers meant in principle that a subsea cable could be sourced from two vendors, the cable vendor and the cable landing station optical equipment. So it became customary for a large consortium to purchase the wet plant from ASN or Subcom or NEC and the dry plant from another vendor like Ciena or Infinera. But the traditional consortium model involved owning a fraction of lit capacity, not fibre pairs. So the consortium could choose only one dry plant vendor for equipment, power and software management tools. 

Between 2010 and 2020 new subsea cables had as many as six to eight pairs and it was common to see a consortium member purchase a pair or two for itself. For example, Telecom Malaysia took two pairs on the ASE system. But most consortium members had no such great needs or the ambition to manage fibre pairs themselves. It was the advent of spatial division multiplexing (SDM) that led to fibre pair ownership becoming commonplace on consortium cables. SDM meant that subsea cables could have from 12 to 36 pairs. Furthermore, the US digital titans were now the dominant traffic drivers. So they began financing most big capacity systems and they had no interest in a lit capacity model where they must reach a consortium consensus and make typical bureaucratic compromises. Facebook, Google, and Amazon saw that fibre pair ownership allowed each owner complete freedom to select the technology they thought best. So Google and Facebook became submarine cable banks and the open cable model made it easy to sell excess pairs and spectrum to the carriers because the buyer had complete technology freedom of choice. Here is a Ciena guide to the open cable model: https://www.ciena.com/__data/assets/pdf_file/0013/29011/Open_Submarine_Cables_Ebook.pdf.