Subsea Cables & Internet Infrastructure

These two Subco-owned cable systems have experienced ongoing outages that started August 8th. Each has a shunt fault located very near the other in the Perth cable protection zone. This zone extends from shore to a depth of 2000 meters and is over 100 kilometers long. These protection zones can backfire because their width is usually just a nautical mile. So the cables are packed together like sardines and if a ship drags its anchor, then multiple outages are pretty much guaranteed. It raises the question of whether cable protection zones are really a good idea since the level of shipping pretty guarantees cable damage. In a way, cable protection zones violate the principle of resiliency via physical diversity. The most likely suspect in this case is a ship that dragged its anchor across the two cables and damaged the sheath protecting the power conductor from water. A ship has been identified that was in the area at the time the outages began. Cable repairs are slated to be complete A...

If you have ever heard someone say they bought a quarter or half fibre pair, it means they bought the right to use a slice of laser spectrum to create transport services. Think of spectrum as clay and optical waves as the finished product. The spectrum seller places a filter on a fibre pair that ensures the buyer only gets the purchased frequencies. A quarter fibre pair means they get 25% of the pair's total usable spectrum. Similarly, for a half fibre pair.  In general, the minimum commercial purchase is 560 Gigahertz. The amount of usable bandwidth depends on the modulation or encoding scheme. Complex encoding schemes generate more zeros and ones than simple ones. And they cost proportionally more. Using standard Ciena gear, you can squeeze about 2.5 terabits of usable capacity out of the 560 Ghz allotment. Below is the basic topolgy. Richard Norris of Ciena (2025 Suboptic Spectrum Working Group) created the slides.  Spectrum is like any other service. You can lease or buy i...

Lasers produce coherent light. This means the electromagnetic waves have the same frequency, move in the same direction, and their phase repeats in a regular pattern. The practical implication is that the laser light remains in a tight, focused band as opposed to spreading over time. This prevents the signal strength or optical power from rapidly diminishing. However, in telecommunications, coherent optics is more than just laser light. It has two key ingredients, advanced modulation schemes that use combinations of amplitude and phase to create higher bandwidth. The other component are digital processing chips (DSPs). Laser light is subject to nonlinear errors due to chromatic and polar dispersion. The DSPs can detect these errors and recover the original pristine signal. Digital signal processing detects nonlinear errors using mathematical algorithms called forward error correction. 

A fibre optic subsea cable is encased in a polyethylene sheath. Most damage due to fishing trawlers, current abrasion, and anchors occurs in water depths 1,000 meters or less. Hence cables laid or buried in shallow waters are usually single or double armored to protect them. The armor consists of galvanized or stainless steel wires wrapped around the white polyethylene layer. Galvanized steel wire has a zinc coat that resists salt water corrosion. While armor does protect against abrasion and small mechanical forces, it is not strong to prevent the cable being torn by sea floor trawler net or a dropped or moving anchor.

A shunt fault is damage to the insulation around the power conductor that all subsea cables require for undersea optical amplification. It causes an electric short. They are most common in the deep sea where the cable lies exposed on the sea floor as opposed to near shore where burial is routine. Abrasion caused by deep sea currents that rub cables against sharp surfaces like rocks are the usual suspects. Depending on the extent of the abrasion, a shunt fault may or may not cause an outage. It depends on the ability of off-shore power facilities to compensate for a partial loss of voltage. When I was worked at Hibernia Atlantic, our cables experienced shunt faults that did not disrupt service. A cable ship would be dispatched to fix it. Below is a shunt fault on Subco's Oman/Australia cable. You can see the power burns on the eroded insulation. 

An Irish company, MDM, whose founding members have done a lot of design work for hyperscalers, has announced it is building two Trans-Atlantic cables in addition to its Pisces project that will connect Ireland to Europe. The estimated construction cost is $500 million. The network is a classic dual ring design where the Northern cable lands at Galway and on Long Island. Now there are several Long Island cable landing stations and MDM already operates one in Galway. So MDM may use these existing facilities for its project. In contrast, the Southern cable is expected to land at a new CLS on Ireland's South Coast. On the US side it will land in New Jersey where it will probably use the existing Wall Township CLS. The fibre pair will probably 16.  I have concerns about this project because there is nothing to indicate it is fully funded. In fact, the last carrier financed and led project across the Atlantic was Aquacomms' AEC-1 cable that went live in 2016. EXA recently purchased ...

Light takes .489 milliseconds or roughly a half millisecond to go 100 kilometers. Get the route miles and you have a great approximation because optical amplifiers or end point electronics have little impact. So Dunant is 13,200 kilometers CLS/CLS. That is 132 times a half millisecond or 66 milliseconds RTD. For full details, click on https://www.m2optics.com/blog/bid/70587/calculating-optical-fiber-latency.