Submarine communication cable

Also called: Undersea cable · Topic: World Transport and Communication · NCERT: Beyond NCERT

Meaning

A submarine communication cable (also called an undersea cable) is a fibre-optic cable laid on the seabed to carry data between countries and continents. About 99% of international internet traffic travels through these cables, so they form the main network of the global internet [7]. A cut in one busy sea passage can slow the internet across whole regions, which makes them critical infrastructure.

Explanation

How it works

• Optical fibre cable (OFC) is made of thin threads of glass. They carry data as pulses of light, not as electric current.
• Light carries far more data, far faster, than copper wire.

• It is hard to tap and almost error-free, because electrical interference does not affect it.

• The cable links two shores.

• It is laid along the seabed between two countries or continents.
• At each end it comes out of the sea at a cable landing station (CLS), the place on the shore where it joins the land network.

• From there, land cables carry the data to cities, data centres and homes.

• Cables carry more than satellites.

• Satellites are useful for remote places and ships.
• Cables carry much more data with lower latency (the delay before a signal arrives).
• So most global traffic stays on the seabed [7].

From telegraph wire to fibre

• 1858: the first transatlantic telegraph cable was laid. It carried fewer than 750 messages and failed after about three weeks [8].
• 16 August 1858: Queen Victoria sent the first message to US President James Buchanan. It took more than 16 hours to send [9].
• 1866: the first cable that worked for a long time linked Ireland and Newfoundland (Canada) across the North Atlantic [8].
• Same period as the Suez Canal (1869): ships moved goods, and cables moved news and orders. Empires and trading firms became more closely linked.
• Later, telephone companies replaced copper wire with OFC. In the 1990s, information became digital (sent as 0s and 1s), so telecommunication and computers merged to form the internet.

Size of the network today

• Over 500 commercial cables, about 1.7 million km long in total [7].
• Together they carry hundreds of terabits of data every second [7].
• Each cable is designed to last about 25 years [7].
• Cable capacity has grown by about 40% a year over the past 40 years [7].

What threatens the cables

• How often they break: usually 150–200 cable incidents a year, or about 3–4 a week [7].
• Human activity causes about 80% of breaks [7]:
• ship anchors dragged along the seabed;

• fishing trawlers (boats pulling heavy nets along the bottom).

• Natural hazards cause the rest: earthquakes, undersea landslides and volcanic eruptions. Tonga has had three major cuts since 2019 [7].

• Chokepoints (narrow sea passages where many cables bunch together):
• One accident there can cut several cables at once.

• Red Sea, 2024: cable cuts disrupted about 25% of data traffic between Europe and Asia [7].

• Sabotage: deliberate cuts are suspected in the Baltic Sea.

• Too few repair ships:
• A specialised ship must find the break, lift the cable, join in a new piece and lay it back.
• Few such ships exist, so a repair can take weeks.

Where it occurs

• World
• North Atlantic: the first lasting cable, from Ireland to Newfoundland (1866) [8].
• Red Sea: cables run through the Bab-el-Mandeb strait and the Suez route, the same corridor that ships use. This is a key Europe–Asia chokepoint [7].
• Baltic Sea: site of suspected sabotage.

• Tonga (South Pacific): three major cuts since 2019, caused by natural hazards [7].

• India's main landing hubs

• Mumbai: Arabian Sea coast, Maharashtra.
• Chennai: Bay of Bengal coast, Tamil Nadu.

• Kochi: Arabian Sea coast, Kerala.

• Chennai–Andaman & Nicobar Islands (CANI) cable

• Inaugurated in August 2020. It is about 2,313 km long and runs across the Bay of Bengal [1].
• It links Port Blair and seven other islands: Little Andaman, Car Nicobar, Kamorta, Great Nicobar, Havelock, Long Island and Rangat [1].

• It has four fibre pairs. Each pair can carry up to 6.4 Tbps (terabits per second) [2].

• Kochi–Lakshadweep Islands (KLI-SOFC) cable

• Inaugurated at Kavaratti on 3 January 2024. It is 1,868 km long, runs across the Arabian Sea and cost ₹1,072 crore plus taxes [3].
• It reaches 11 islands: Kavaratti, Agatti, Amini, Kadmat, Chetlet, Kalpeni, Minicoy, Androth, Kiltan, Bangaram and Bitra [3].
• It gives about 100 times faster internet than the earlier satellite links [3].

Don't confuse with

• Satellite communication: satellites reach remote areas and ships, but cables carry about 99% of international internet traffic at lower delay [7]. "Satellites carry most global data" is a trap.
• Copper telephone wire: copper carries electric current, while optical fibre carries light pulses. Fibre carries more data, is faster, is harder to tap and is almost error-free.
• Telegraph cable (1858/1866): the early undersea cables carried Morse code (letters sent as short and long electric pulses) on wire. Modern submarine cables are fibre-optic and carry digital data [8].
• CANI vs KLI-SOFC: CANI links Chennai and Port Blair across the Bay of Bengal (2020) [1]. KLI-SOFC links Kochi and Kavaratti across the Arabian Sea (2024) [3].

Prelims Hooks

• Submarine cables carry about 99% of international internet traffic. Older estimates said 95% or more [7].
• The main cause of cable faults is human activity (anchors and fishing trawlers), about 80%. Natural hazards such as earthquakes cause fewer [7].
• Red Sea cuts (2024) disrupted about 25% of Europe–Asia data traffic. The cables pass through the Bab-el-Mandeb strait [7].
• CANI: Chennai–Port Blair, Bay of Bengal, 2020, about 2,313 km [1]. KLI-SOFC: Kochi–Kavaratti, Arabian Sea, 2024, 1,868 km, 11 islands [3].
• The first lasting transatlantic cable (1866) ran from Ireland to Newfoundland. The 1858 cable failed after about three weeks [8].
• The International Advisory Body for Submarine Cable Resilience was formed by the ITU (International Telecommunication Union) and the ICPC (International Cable Protection Committee). It has 42 members, and its first meeting was on 12 December 2024 [6].

Mains Points

• Submarine cables are critical infrastructure (GS-III).
• About 99% of data runs through 500+ cables [7].
• The cables bunch together at chokepoints like the Red Sea and Bab-el-Mandeb. There they face anchors, trawlers, earthquakes and sabotage.

• So cable security is now part of geopolitics and maritime security [7].

• India's response.

• Island cables (CANI 2020, KLI-SOFC 2024) narrow the digital divide. They bring e-governance, telemedicine, online education, banking and tourism, and they tie strategic islands near the sea lanes to the mainland [1][3].
• TRAI (Telecom Regulatory Authority of India) made recommendations in June 2023. It proposed government help to fund Indian-flagged repair ships, cable depots on both the west and east coasts, two types of landing station (Main CLS and CLS-PoP), and a waiver of Right-of-Way charges on OFC links to landing stations [4].

• Data-centre capacity has grown from 375 MW in 2020 to more than 1,500 MW [5]. India needs more landing stations on both coasts so that it does not depend only on Mumbai and Chennai.

• Building resilience.

• Spread cable routes across more landing points on both coasts.
• Add more repair ships.
• Work with other countries through the ITU–ICPC Advisory Body, which held a summit in Abuja, Nigeria, in February 2025 [6].
• Together these steps lower the risk that a single cut stops a region's economy.

Related concepts

• Communication
• Telephone and telegraph
• Telecommunication
• Mass media
• Optical fibre cable

Read more

• Communication: telegraph and telephone to optical fibre and submarine cables