Submarine cables play a critical role in global interconnected networks, carrying about 99 percent of international communications traffic. Sharp growth in demand for data, fueled by bandwidth-intensive applications such as video and a proliferation of cloud-based services, has driven a considerable uptick in global submarine cable deployments.
The last five years have seen an average 26 percent increase in available capacity per year on major routes.
The Basics of Submarine Cable
The history of submarine communications cables goes back to 1850, when the first cable was laid across the English Channel to allow telegraph communications between the United Kingdom and continental Europe.
Today, submarine cables use fiber-optic technology, whereby information is encoded onto waves of light transmitted by lasers across thin glass fibers. The throughput varies with optical technology used, but today’s most advanced fiber links are capable of transmitting over 200 terabits per second.
The capacity actually used—the “lit capacity”—is generally much lower, allowing cable owners to scale up the use to meet customer demand over time, or to accommodate large shifts in Internet traffic if another cable is cut or damaged.
There were approximately 378 submarine cables in service as of early 2019, traversing roughly 1.2 million kilometers, connecting virtually all countries with a coastline. The cables run along the ocean floor joining nations that have large volumes of traffic to exchange.
Near to shore, the cables are shielded and buried to protect against potential runins with anchors, wildlife, fishing trawlers, etcetera. However, in deeper parts of the ocean, where damage is less likely, cables run along the surface of the ocean floor and are as thin as a garden hose.
Even with shielding and burying, each year sees more than 100 cable faults on average, usually due to fishing trawlers or anchors, but occasionally from natural disasters such as earthquakes. The risk of other types of disruption are low, but material given the importance of undersea cables.
Ownership And Control
One area where there are more disruptions than average is the Strait of Malacca. This busy shipping corridor contains more than a dozen cables connecting a large majority of the traffic between Asia, India, the Middle East, and Europe.
The Strait of Malacca is one of several choke-points where geographic constraints, or political or territorial constraints limit potential cable routes. Other key choke-points include the Strait of Luzon (between Taiwan and the Philippines, the Red Sea), and the crossing of Egypt.
Submarine cables are predominantly owned by consortiums of telecommunications carriers that join together to pay for these expensive projects. In the late 20th century, during the “dot-com” bubble, entrepreneurs took on some private projects, reselling the capacity once it was completed.
In recent years, major web companies, such as Google, Facebook, Microsoft, and Amazon have increasingly invested in their own cables, outpacing the traditional Internet backbone providers.
Other Challenges Facing Submarine Cables
The case for a new research agenda focused on characterizing the global submarine network and the critical role it plays as an essential component of any inter-continental end-to-end connection is paramount. The submarine network’s role as mainstay of the world’s economy, security and well-being, provides clear motivation for such an agenda.
Beyond this, from an intellectual perspective, the network’s scale, management complexity, and opaque architecture pose significant research challenges. Criticality and scale interact in unexpected ways. As the total length of submarine cables continues to expand rapidly, so too does the chance of network disruptions due to cable problems.
For starters, there is a number of potential risks stemming from their natural environment from large scale disasters like earthquakes and tsunamis, to undersea landslides and ocean currents that can scrape cables across the rocky surfaces on the ocean floor, to even sea-life attacks on less protected cables.
Even more than natural forces, human actions intentional or not are considered the biggest threat to cables, with approximately 70% of disruptions being caused by fishing trawlers and ship anchors, as well as growing concern over intentional attacks on vulnerable cables.
For instance, US Navy officials have stated concern upon observing Russian submarines and spy ships operating near important submarine cables. While the high degree of connectivity available in certain areas may limit the consequence of these problems, other regions appear to be particularly vulnerable.
The $560-million Asia America Gateway cable (AAG), notorious for frequent breakdowns, connects Southeast Asia and the US, handling over 60% of Vietnam’s international Internet traffic. In 2017 alone, the AAG has suffered at least five technical errors.
In another incident, divers off the coast of Egypt were arrested for cutting the SE-WE-ME-4 submarine cable, leading to a 60% drop in Internet speeds. Other incidents have resulted in entire countries being taken offline due to a single submarine cable cut, such as Mauritania in April 2018.
Researchers trying to characterize the submarine network and its role as a component of the global network face a number of challenges. For starters, submarine cables are commonly managed by consortia and shared by multiple network operators. As a result, routes that appear to be distinct paths at the network layer may rely on the same cable at the physical layer.
Furthermore, for particularly critical routes (e.g., transpacific or transatlantic) large network operators often utilize multiple cables.
Thus, even with the full details on the underlying topology, our lack of visibility below Layer 3 makes it difficult to map specific network routes to their underlying conduits and quantify the dependence of Internet connections on particular submarine cables.