Submarine cables are the backbone of the internet, carrying 99% of all international telecommunications traffic for personal, business, and government use. While we live in an increasingly wireless world, that connectivity depends on little-known underwater internet cables, which are physical links lying on ocean floors, and often referred to as submarine cables, subsea cables, or undersea cables.

In total, there are approximately 450 submarine cable systems in-service around the world, which together span over 850,000 miles (1.35 million kilometers) and form a critical part of the internet’s infrastructure. As demand for data continues to grow, driven by mobile device usage, cloud computing, and new wireless technologies like 5G, the amount of data traveling across this physical submarine cable infrastructure has increased rapidly in tandem.

What is a Subsea Cable?

Physically, subsea cables comprise undersea fiber optic cables laid on the ocean floor, which consist of bundled glass strands that transmit data between two or more landing points. To protect these optical fibers from damage, they are covered in silicon gel and wrapped in multiple different layers of plastic, steel wires, copper sheathing, polyethylene insulator, and nylon yarn. At the same time, this physical encasement guards the optical fibers from signal degradation.

Submarine Cable Cross Section
Diagram: 1) polyethylene insulator, 2) copper sheathing, 3) steel wires, 4) optical fibers in silicon gel.

Also, subsea cables contain a number of repeaters (or optical amplifiers), which amplify the signal along the length of the cable, over regular intervals, such as every 60 miles (100 kilometers), as the cables traverses across the ocean. At each end, submarine cables reach land within a cable landing station (CLS), from where data is then routed, via terrestrial fiber optic cables, to its final location. Cable landing stations function as a data center, with power and networking equipment to control a submarine cable’s operations and to allow data traffic to flow.

Above is an example of Google Cloud connecting its data center in Northern Virginia (left) to another one of its data centers in Belgium (right), via a trans-Atlantic submarine cable, landing on the west coast of France.

Submarine cables connect continents and their countries, mainland to islands, islands to each other, or several points along a coast. As such, undersea cables are interconnecting locations that have a coastline but do not share land borders, for example, between the United States and the United Kingdom. More specifically, major global subsea cable routes, by region, are as follows:

  • Trans-Atlantic: New York to London (most competitive route globally)
  • Trans-Pacific: Los Angeles to Tokyo, Los Angeles to Hong Kong, Los Angeles to Singapore, Los Angeles to Sydney
  • Americas: Miami to São Paulo, Miami to Fortaleza (Brazil), New York to São Paulo
  • Intra-Asia: Tokyo to Singapore, Hong Kong to Singapore, Singapore to Mumbai
  • EMEA-to-Asia: London to Singapore, Marseille to Mumbai (higher latency routes)

Global network providers such as AT&T, Lumen Technologies, and Zayo, all operate terrestrial fiber optic networks and interconnect these networks between North America, South America, Europe, Asia, Africa, and Australia, through submarine cables.

How Long are Subsea Cables?

Subsea cables are often thousands of miles / kilometers in length. On the longer end, submarine cables traversing trans-Pacific or EMEA-to-Asia routes (e.g., SEA-ME-WE 6) can reach more than 10,000 miles (16,000 kilometers) in length. While on the shorter end, subsea cables connecting nearby islands or countries (e.g., Scylla) can be approximately 100 miles (160 kilometers), or less, in length.

How Long Submarine Cables Stretch Along the Sea and Ocean Floor

Additionally, certain undersea cables connect only two landing points across a body of water, whereas other cables have multiple landing points, connecting multiple countries.

What is the Longest Undersea Cable?

Currently, the longest operational submarine cable is the SEA-ME-WE 3 (South-East Asia-Middle East-Western Europe 3) system, which spans 24,233 miles (39,000 kilometers) and has multiple points of connectivity, in Europe, the Middle East, and India.

SEA-ME-WE 3 Route and Landing Points
SEA-ME-WE 3 Route and Landing Points Map

However, the 2Africa system, which is being developed by Facebook (Meta), will ultimately become the longest submarine cable, spanning 27,962 miles (45,000 kilometers), thus usurping SEA-ME-WE 3. In terms of timing, the 2Africa subsea cable system will be ready for service (RFS) in 2024.

2Africa Route and Landing Points

READ MORE: Top 100 Subsea Cable Systems in the World

Recent History of Submarine Cables

Over the past 20+ years, the submarine cable industry has gone through several distinct periods of expansion and contraction, driven, in large part, by supply and demand for international bandwidth:

Early-to-Mid 2000s

During the dotcom bubble, billions of dollars in speculative investments funded new submarine cable builds, which resulted in excess capacity (i.e., supply) in the early 2000s. Without the requisite demand for capacity, many subsea cable networks struggled financially and ultimately, their parent companies went bankrupt (e.g., Global Crossing). As a result, the submarine cable market went through a period of approximately 10 years with no cables being built.

Early-to-Mid 2010s

Between 2011 and 2015, the submarine cable market was characterized by slow growth in new system deployments because of economic uncertainty, as well as the alternative to simply upgrade existing cable systems, which was more cost-effective.

During this period, subsea cable demand centered on new and developing markets, particularly intra-Asia routes, as well as building-out route diversity to enhance network resilience. For example, intra-Asia systems, including the South-East Asia Japan Cable (SJC) and Asia Submarine-cable Express (ASE), became ready for service (RFS) in this early-to-mid 2010s timeframe.

Mid-to-Late 2010s

During the years 2016 through 2019, cloud service providers (CSPs) and over-the-top (OTT) media service companies, collectively known as hyperscalers, emerged as major investors in new subsea cables. In particular, the rapid growth and use of services from Amazon, Facebook (Meta), Google, and Microsoft, drove most of the demand for new trans-Atlantic submarine cables. For example, the MAREA submarine cable, which was 50%-funded by Facebook (Meta) and Microsoft, became ready for service (RFS) in early 2018.

2020 to Present

Presently, strong demand remains for high-bandwidth, low-latency, and high-redundancy submarine cable capacity, particularly in the trans-Atlantic and trans-Pacific regions. Notable subsea cables being constructed in this time period include hyperscaler-funded projects such as Dunant, Equiano, Firmina, Grace Hopper, and Topaz, and consortium cables like 2Africa, Apricot, Bifrost, Blue, Echo, Havfrue, Raman, and SAEx (South Atlantic Express).

How are Internet Cables Laid in the Sea and Ocean?

Submarine cables are laid on the sea and ocean floor using cable laying ships, which are specially designed seagoing vessels that can be over 500 feet (150 meters) long. These cable laying ships load millions of pounds / thousands of tons of fiber optic cable, by spooling it into large tanks onboard the vessel.

Overall, this fiber optic cable spans thousands of miles / kilometers in length. Additionally, cable laying ships typically hold tens to hundreds of repeaters onboard.

Cable Laying Ship Cable Innovator London

As an example, Google Cloud’s Topaz submarine cable is being laid by Orange Marine’s cable laying ship named René Descartes. Specifically, the René Descartes ship will carry 10.2 million pounds (5.1k tons) of fiber optic cable, repeaters, a plough, and a remote operating vehicle (ROV).

Cable Laying Process

Deploying submarine cables involves several steps including route planning, marine survey, operational permitting, design, manufacturing, marine lay, and installation & commissioning. Once the submarine cable is loaded on to a cable laying ship, the vessel can stay at sea for months, while it progresses on laying the underwater internet cable directly onto the ocean floor.

Overall, the process for laying submarine cables typically takes 1 to 3 years, to deliver the system from route planning to an operational asset.

How Deep are Internet Cables Laid in the Sea and Ocean?

Once out in the sea or ocean, submarine cables are laid in deep water where they can lie on relatively flat parts of the ocean floor, avoiding contact with large rocks. For example, trans-Atlantic subsea cables, which traverse the Atlantic Ocean, are laid at depths of approximately 13,000 feet (4,000 meters) at their deepest point.

How Deep are Internet Cables Laid on Sea and Ocean Floor which Extends into the Distance

As a reference point, the Atlantic Ocean has an average depth of 12,000 feet (3,650 meters). However, as part of route planning, submarine cables tend to be laid on routes that avoid the maximum depths of an ocean (e.g., oceanic trenches).

In contrast, as submarine internet cables approach coastlines, a plow is used to dig trenches and bury the cables on the ocean floor. This is done to protect them from damage and prevent corresponding cable faults.

Cable Faults

Subsea cable faults occur when fiber optic submarine cables are damaged, leading to disruptions in data transmission across networks. These cable faults are often caused by natural events like earthquakes, underwater landslides, or human activities such as fishing and ship anchors.

Repairing these submarine telecommunications cable faults requires specialized ships to locate and fix the damaged sections, which can be a time-consuming and costly process due to the challenging underwater environment. The repair time can vary from a few days to several weeks, depending on the severity and location of the damage.

Who Supplies and Installs Submarine Cables?

The majority of the design, manufacturing, and deployment of submarine optical networking equipment is performed by a small group of cable companies, who act as a system supplier and/or installer.


Major suppliers of submarine cable systems, which manufacture the undersea fiber optic cables, include Nokia’s Alcatel Submarine Networks (ASN), HMN Technologies (formerly Huawei Marine Networks), NEC (OCC Corporation), and SubCom.


Prominent installers of submarine cable systems each own fleets of 5 to 8 cable laying ships. Presently, the most active installers of submarine cables globally, include SubCom, Alcatel Submarine Networks (ASN), Orange Marine, and Global Marine Systems.

How Much Does an Underwater Internet Cable Cost?

Bringing a submarine cable from route planning to being ready for service (RFS) involves multi-million-dollar capital investments, which largely correspond to the length of the planned cable. For example, a new trans-Atlantic subsea cable currently costs $200 million to $250 million to build. As a rough approximation, a typical submarine cable can be built at a cost of approximately $40,000 per mile, which is equivalent to $25,000 per kilometer.

Who Owns the Undersea Internet Cables?

Historically, there have been two different types of submarine cable system ownership models: consortiums and private.

Owners of Underwater Internet Cables with Tiny Lights Glowing Around the Fiber Optics


Traditionally, submarine cables were owned by telecommunications carriers, who would form a consortium among parties interested in securing capacity on the cable. In turn, these carriers could share the manufacturing/supplier costs, as well as outlays needed to install the submarine cable. For their financial commitment, carriers would be able to use a portion of the underwater internet cable’s capacity.

For example, one of these carriers, Lumen Technologies, which is comprised of assets from cable operators previously known as CenturyLink and Level 3 Communications, now owns and leases a global network which includes 42k route miles (67.5k route kilometers) of submarine fiber optic cable systems.

More recently, cloud service providers (CSPs) and over-the-top (OTT) media service companies, collectively known as hyperscalers, have also become involved in these consortiums.


Beginning in the mid-to-late 2010s, these hyperscalers also began developing private submarine cables, either independently or with very few owners, as compared to the consortium model. In so doing, these hyperscalers shifted their strategy from solely being buyers of wholesale network capacity, to being owners of that network capacity through subsea cables.

More precisely, hyperscalers including Amazon, Facebook (Meta), Google, and Microsoft have become major investors in new submarine cables due to their need for high-bandwidth, low-latency, and high-redundancy capacity to power their applications.

Who Uses Submarine Cables?

Users of submarine cable capacity are, in many instances, the same cable operators that own the infrastructure. Specifically, significant users of subsea cable capacity include telecommunications carriers, mobile network operators, cloud service providers (CSPs), and over-the-top (OTT) media service companies. In addition, multi-tenant data center operators, financial services companies, government agencies, and large enterprises are also key customers of ocean internet cable owners.

Demand Drivers of Underwater Internet Cables

Demand for new submarine cables and capacity upgrades are primarily driven by capacity needs, as a result of growing data traffic volumes, and greater connectivity needs. In particular, cloud service providers (CSPs) and over-the-top (OTT) media service companies are driving this growth, as they currently comprise approximately 2/3rds of international internet traffic.

Data is Driving the Infrastructure Need

Demand for bandwidth is expected to double every two years, over the medium-term. This growth in bandwidth requirements is being driven by an increasing number of users, coupled with greater data consumption per user. More specifically, examples of the applications from cloud service providers and content/OTT media services, that are driving data demand, include:

  • Amazon: Amazon Web Services (AWS), Prime Video, (Retail), Kindle, Twitch
  • Microsoft: Bing, Azure, Microsoft 365, Microsoft Teams, Dynamics 365, OneDrive, LinkedIn, Skype, Xbox,
  • Alphabet: Gmail, Google Drive, Google Maps, Google Photos, Google Play, Search, YouTube, Google Cloud
  • Meta Platforms: Facebook, Instagram, Messenger, WhatsApp, Metaverse, Oculus
  • Content/OTT: Netflix, Hulu, Disney+, HBO Max, Apple TV+, Paramount+, Peacock, Discovery+

Overall, new submarine cables supply the international bandwidth capacity that is needed, to satisfy the tremendous demand for more data traffic, which is being driven by applications from companies including Amazon, Microsoft, Alphabet, and Meta Platforms.

Route Diversity

At the same time, route diversity, redundancy, and more direct control over critical infrastructure is driving the need for more submarine cables. Specifically, having bandwidth available on multiple subsea cable systems is important, in order to provide a high level of network availability and reliability.

Demand for route diversity is particularly being driven by the hyperscalers – cloud service providers and OTT media services – who need to control their own infrastructure. Furthermore, these hyperscalers are not necessarily seeking the same routes as telecommunications carriers. For example, in certain instances, hyperscalers are deploying submarine cables for international data center-to-data center connectivity purposes. Indeed, these routes often do not link major international cities together, which has been the traditional focus of carriers.

Key Characteristics of Submarine Cables

Submarine cable systems are often benchmarked between each other using key characteristics such as capacity, fiber pairs, and useful life.

Important Characteristics of Subsea Cables Featuring Concentric Circles and Shape


Over the past few decades, capacity on new subsea internet cables has increased from hundreds of megabits per second (Mbps) of capacity, to systems with hundreds of terabits per second (Tbps) of capacity, at present. Predictably, newer ocean internet cables are capable of carrying significantly more data than cables laid 10, 20, or 30 years ago.

As an example, the MAREA submarine cable, which currently operates between Virginia Beach (United States) and Sopelana (Spain), offers 200 terabits per second (Tbps) of capacity. In comparison, Global Cloud Xchange’s FLAG Europe-Asia (FEA) undersea cable, which became ready for service (RFS) in 1997 and traverses an EMEA-to-Asia route, only provides approximately 500 gigabits per second (Gbps) of capacity.

Notably, only around 20% of a submarine cable’s total design capacity is lit capacity, meaning the capacity that is being utilized by the end user. These significant capacity buffers are normal industry practice because they allow for underwater internet cable systems to respond to unexpected spikes in demand, such as carrying traffic that is rerouted from other systems following a cable fault.

What is the Highest Capacity Submarine Cable?

Currently, the highest capacity submarine cable in operation is Google Cloud’s trans-Atlantic system called Dunant, which spans 4.1k miles (6.6k kilometers) across the Atlantic Ocean, connecting Virginia Beach (United States) with Saint-Hilaire (France). Particularly, Dunant has a capacity of 250 terabits per second (Tbps), across 12 fiber pairs.

Fiber Pairs

Fiber pairs are two individual fiber strands that are paired together for bi-directional, meaning transmit and receive, communication. Historically, submarine cables were built with 4 to 8 fiber pairs. However, presently, these new ocean internet cables are being built with 12, 16, 24, and 36 fiber pairs.

Individual fiber pairs can be retained by the owner of a undersea cable or they can be individually leased to third-parties, in order to monetize the infrastructure’s capacity.

What is the Useful Life of a Submarine Cable?

Submarine cables face two ends to their useful life: physical and economic.


The physical useful life of a submarine cable occurs when it no longer functions and, thus, needs to be retired. Typically, these underwater internet cables are engineered to have a minimum design life of 25 years.


The economic useful life of a submarine cable occurs when the costs to operate the system outweigh the cable’s revenue potential from leasing its capacity. Newer undersea cables displace older systems because they can operate at a similar level of fixed costs, but, given their higher capacity, their cost per bit delivered is much lower.

As such, older submarine cables reach economic obsolescence and are forced into retirement once their contractual revenue agreements end. Therefore, an underwater internet cable’s economic useful life can be shorter than 25 years, meaning less than the physical useful life benchmark.

Technological Innovations in Subsea Cables

In the dynamic realm of subsea communications, technological innovations such as Space-Division Multiplexing (SDM), Multi-Core Fiber, and Open Cables are revolutionizing the way data is transmitted across ocean depths.

Tech Innovations in Submarine Cables Displayed by the Sheath Pulled Back to Reveal Fiber

Space-Division Multiplexing (SDM)

Space-Division Multiplexing (SDM) is a significant advancement in the technology of subsea communication cables, enabling the creation of multiple spatial paths within a single fiber by establishing several parallel spatial channels. This innovation greatly increases the total data capacity of the cable. For example, SDM uses more fiber pairs, such as twelve, compared to the traditional six or eight found in conventional underwater cables.

A key advantage of SDM is its ability to allow multiple fiber pairs to share pump lasers and other optical components. This contrasts with traditional subsea cables, where each fiber pair requires its own dedicated set of pump lasers. Implementing SDM is not only technologically advanced but also cost-effective. It enhances the cable’s capacity without significantly increasing costs.

The Dunant undersea cable, deployed by Google, was the pioneer in utilizing SDM technology, connecting Virginia Beach, Virginia, in the United States with Saint-Hilaire-de-Riez, France. The Dunant cable is equipped with power-optimized repeater designs, a crucial element of SDM technology, ensuring efficient signal amplification along its 3,977-mile (6,400-kilometer) length.

Notably, Dunant incorporates 12 fiber pairs. Currently, new subsea cables are being constructed with up to 24 fiber pairs. In the near future, SDM is expected to enable the installation of underwater cables with 32, 48, or even 64 fiber pairs.

Multi-Core Fiber

Multi-core fiber technology utilizes fibers that contain multiple cores, unlike traditional single-core fiber. Each core operates independently within the fiber, effectively multiplying the data-carrying capacity of the cable.

This technology is particularly valuable for subsea cables, offering a significant bandwidth increase – by doubling the number of cores in a fiber – without the need for larger or more cables. It also leads to lower costs per bit and streamlines manufacturing, testing, and maintenance processes.

The faster implementation of multi-core fiber technology over traditional single-core fibers is evident in its application by Google and NEC in a new cable: the Taiwan-Philippines-U.S. (TPU) subsea cable system.

Open Cables

Open Cables is a concept in submarine telecommunications where the cable system is designed for compatibility with multiple types of networking equipment, rather than being tied to a specific vendor. This approach fundamentally separates the ‘wet plant’ components (which include the cable, repeaters, and branching units) from the ‘dry plant’ elements (namely the optical transmission equipment).

Adopting the Open Cables strategy provides significant advantages. It offers greater flexibility and choice for cable system owners and operators, particularly in selecting transmission equipment vendors. This can lead to cost savings and facilitate easier system upgrades. Furthermore, this approach fosters innovation by allowing the integration of diverse and emerging technologies, as they become available.

Jonathan Kim covers Fiber for Dgtl Infra, including Zayo Group, Cogent Communications (NASDAQ: CCOI), Uniti Group (NASDAQ: UNIT), Lumen Technologies (NYSE: LUMN), Frontier Communications (NASDAQ: FYBR), Consolidated Communications (NASDAQ: CNSL), and many more. Within Fiber, Jonathan focuses on the sub-sectors of wholesale / dark fiber, enterprise fiber, fiber-to-the-home (FTTH), fiber-to-the-premises (FTTP), and subsea cables. Jonathan has over 8 years of experience in research and writing for Fiber.


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