Introductory Schematic of Subsea Cable Architecture

1. The submarine line termination equipment, consisting of active electronics and transponders (lasers and optical receivers), was traditionally kept at the cable landing station. This began changing when carriers wanted to own and manage their own dedicated capacity (fibre pair or spectrum slice). Telekom Malaysia was an early example. It took two fibre pairs on the ASE cable as opposed to a fraction of the consortium lit capacity. Later the hyperscalers crystallized this evolution in the open cable model which limits common ownership to the wet segments. Each owner has either fibre pairs or spectrum and makes its own decisions concerning where to place the SLTEs. Because cable landing stations are not designed as large carrier neutral interconnection points, the SLTEs are almost always housed in a cage at a carrier netural data center. It is this flexibility in choice of location and equipment vendor that makes the open cable model so appealing. It also facilitates hyperscalers building large cable and partly financing them via fiber pair or spectrum sales.

2. While the fibre between data centers and the CLS is know as backhaul, the fibre linking the CLS to the beach manhole is known as front haul. The wet segments extends from beach manhole to beach manhole. They include the cable and the optical amplifiers, often called repeaters. A third component are branching units, which despite the diagram, definitely do not float. 😃 Very often branching units are deposited on the ocean floor during a deployment in case a particular country wants to join the cable system. For example, Equinano dropped branching units all along the African West Coast. But so far there have been no takers because the cost of completing connection to a CLS has been in the range of $20 million to $35 million dollars. Branching units in the beginning simply split the existing fibre pairs into two paths. This enabled a linear cable to land in two countries. Then they developed fibre pair mechanical switching and later wavelength switching. These developments enable capacity to allocated to where there is the most demand and need. 

3. Optical amplifiers are typically spaced 70 to 90 kilometers. 

Diagram of the Essential Elements of a Fibre Optic Subsea Cable


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