How submarine cables work, why we need them
Almost all internet data travels through undersea fibre-optic cables, and Bangladesh is expanding its submarine cable network to improve speed, capacity, and global connectivity
Being constantly engrossed in wireless communication thanks to the rapid advancement of digital infrastructures for day-to-day operations, it often feels like we are immersed in a sea of online activities and the internet travels invisibly through the air.
However, in reality, nearly 99% of data traffic — everything from emails and video calls to banking transactions — moves through submarine cables laid across the ocean floor.
What are submarine cables?
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Submarine cables are long, thin strands of glass fibres protected by layers of steel wire, copper, and waterproof insulation. Each cable is typically about the thickness of a garden hose, but it can stretch for thousands of kilometres across the ocean floor.
Inside, the glass fibres carry pulses of light—representing data—at nearly the speed of light, allowing information to travel instantly between distant parts of the world.
Although the cables are designed to be durable, they rest on the seabed and can be damaged by natural disasters or ship anchors. Repairs are carried out by specialised ships that retrieve and fix the broken sections, often under difficult oceanic conditions.
The first undersea cable, laid in 1858, transmitted telegraph messages between the United States and Great Britain. Today's cables, built using advanced fibre-optic technology, can carry terabits of data per second — millions of times more than the earliest copper wires.
How do they work?
At its core, a submarine cable works by transmitting light signals.
Digital information, such as text, images, or video, is first turned into light pulses by laser transmitters. These pulses travel through very pure glass fibres that keep signal loss to a minimum.
Every 60 to 100 kilometres, undersea repeaters boost the signal so it stays strong over long distances; they are powered by electricity running through the cable's copper layer.
When the light reaches land, it enters a landing station where it is converted back into digital data and sent into the local internet network we use every day.
Why are submarine cables needed?
With the advent of satellites, we might think that all internet travels through the satellites and reaches our devices.
Despite the rise of communication satellites, submarine cables remain faster, cheaper, and more reliable for transmitting large amounts of data.
Speed and latency: Fibre-optic cables provide much lower latency than satellites. A signal sent via a cable can reach across the Atlantic in a fraction of a second — vital for financial trading, video streaming, and real-time communication.
Capacity: Modern cables can carry enormous volumes of data, supporting the ever-growing demand from cloud services, social media platforms, and international business.
Cost efficiency: Once laid, cables are more energy-efficient and cost-effective to operate compared to satellite systems. Cables can last 25 years or more with routine maintenance, whereas satellites need regular replacement.
Redundancy and stability: A global network of over 550 active cables, spanning more than 1.4 million kilometres, ensures resilience in global communications.
Meanwhile, satellite signals are impacted by weather and interference, while cables are largely protected beneath the sea.
Finally, cables follow predictable routes, which is important for security, whereas satellite communications are harder to control and secure.
In short, while satellites are important for global connectivity, they cannot substitute the substantial connection achieved through submarine cables.
Who builds and owns them?
Submarine cables are typically funded and operated by consortia of telecommunications companies, tech giants, and governments.
Companies like Google, Meta, Microsoft, and Amazon have invested heavily in their own private cables to guarantee faster and more secure global connectivity for their services.
For example, Google's Equiano cable links Europe to Africa, while the Marea cable (built by Microsoft and Facebook) connects the United States to Spain.
These investments reflect how essential cable infrastructure has become to both global commerce and digital sovereignty.
Submarine cable in Bangladesh
Currently, there are two submarine cable landing stations in Bangladesh. Cox's Bazar station, located near Jhilongja Army Camp, serves as the main gateway for the country's international internet traffic.
Kuakata landing station, situated in the Maitbhanga area, was inaugurated in 2017 and provides additional bandwidth capacity to the country.
Both stations are owned and operated by Bangladesh Submarine Cable Company Limited (BSCCL), a state-owned entity under the Ministry of Posts, Telecommunications, and Information Technology.
In 2022, the Bangladesh Telecommunication Regulatory Commission (BTRC) issued licenses to three private companies — Summit Communications, CdNet Communications, and Metacore Subcom Ltd — to establish, maintain, and operate submarine cable systems in Bangladesh.
These companies have formed the Bangladesh Private Cable System (BPCS) consortium, marking the country's first privately owned submarine cable initiative.
They took up the project to establish the third submarine cable. Initially slated for completion by June 2024, the deadline was first extended to June 2025. The timeline has now been extended to June 2027.
Yesterday (12 October), Faiz Ahmad Taiyeb, the chief adviser's special assistant on posts, telecommunications, and ICT, said Bangladesh is in discussions with Singapore to join the fourth submarine cable network.
He also said, the third submarine cable, with a capacity of 17,000 Gbps, is expected to go into commercial operation by mid or late 2026.
The third submarine cable project, initiated in 2021, aims to connect Bangladesh's Cox's Bazar to Singapore on one end and France on the other. Through the core cable, Bangladesh can gain direct data connectivity with Singapore, India, Djibouti, and France.
