A deep-ocean submarine cable can be only about 17–21 mm wide—roughly garden-hose-sized—because it does not carry data as electrical current through a thick metal wire. Lasers encode data as light, and very fine glass fibres guide that light across the ocean. The surrounding cable protects and supports the fibres; optical amplifiers along long repeatered routes compensate for signal loss. The International Telecommunication Union (ITU) estimates that submarine cables carry approximately 99% of the world’s Internet traffic, though other sources use different estimates and definitions.
How can a small cable carry so much data?
The cable’s small diameter does not limit it to one signal. Its optical fibres carry data as light, and modern cable systems are designed to send many signals through those fibres. The fibres form the information path; the cable’s outer layers provide mechanical and environmental protection. A transoceanic link is therefore a complete engineered system, not simply a long piece of glass.
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From a network to a pulse of light
At one end, terrestrial networks connect to a submarine cable through a landing station. Transmission equipment converts digital data into patterns of light using lasers. The glass fibre guides that light along the route, and equipment at the far landing station reads the optical signal and passes the data into the next terrestrial network.
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1Repair Windows errors before they cause bigger problems2Fix the driver behind crashes, sound loss and screen glitches3Clear out junk files and repair common Windows errorsWhy long routes need repeaters
Light weakens as it travels through fibre. On long, repeatered systems, powered optical amplifiers placed along the route compensate for that loss. The power conductor in the cable supplies electrical power to repeaters and, where applicable, branching units; it is separate from the data signals carried by the glass fibres. An ICPC/UNEP technical account from 2009 gives about 70 km as typical repeater spacing for the system class it describes. That is a historical, source-specific typical value, not a universal spacing rule for present-day cables; route and system designs differ. ITU-T Recommendation G.978 (2025) covers repeatered and repeaterless cable designs as well as cable characteristics and remote power feeding.
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What is inside a submarine cable?
The optical fibres occupy only a small part of the cable. Around them, a system may use protective materials, strength members, power conductors and other components selected for the route and design. The construction varies with water depth and the protection required; there is no single cross-section that describes every submarine cable. ITU-T G.978 sets out characteristics for lightweight, protected, armoured, repeatered, repeaterless and sensing cable types.
| Route section | Reported diameter | Typical protection approach |
|---|---|---|
| Deep ocean | About 17–21 mm, according to the ICPC/UNEP report | Generally laid directly on the seabed; lighter construction can be used where exposure to human activity is lower. |
| Near shore and shallower water | About 40–50 mm where protective wire armour is added, according to the ICPC/UNEP report | More likely to be armoured and buried in exposed areas, where fishing gear and anchors pose greater risks. |
These are reported ranges, not dimensions for every cable. A European Commission Joint Research Centre explainer also describes telecommunications cables as up to 4–5 cm in diameter, consistent with thicker protected sections. The contrast explains why “garden-hose-sized” is a useful image for a deep-ocean cable, but not a precise description of every part of a route.
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Why say submarine cables carry “roughly 99%” of traffic?
The figure is an attributed estimate, not a single precisely defined measure that all authorities state identically. The ITU’s April 2026 “Submarine cable resilience” backgrounder says submarine cables carry approximately 99% of the world’s Internet traffic. NOAA’s “Submarine Cables” page gives a differently framed estimate: over 95% of international data and voice transfers. The figures use different wording and denominators, so they should not be treated as interchangeable measurements.
The point behind either estimate is that submarine cables are central to international connectivity. They link national and regional networks across oceans, while the Internet also relies on terrestrial networks and other infrastructure at each end of a cable route.
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How are routes chosen and cables laid?
A route is surveyed and engineered rather than chosen as a straight line across a map. The survey considers seabed depth and shape, bottom conditions, seasonal temperature variation, currents, seismic activity, existing cables and pipelines, prior faults, fishing and mining, and applicable laws. These factors help reduce engineering risks and conflicts with other uses of the sea. ITU-T Recommendation G.971 (2024) covers route survey considerations along with system features and maintenance guidance.
Deep water and exposed shallows
In deep water, cables generally rest directly on the seabed. Closer to shore, where anchors and fishing gear are more likely to reach them, cable sections are more likely to receive extra armour and be buried. Burial is a protection measure for exposed areas, not a description of how every ocean cable is installed. The European Commission’s Joint Research Centre describes burial alongside monitoring and surveillance as ways to protect cable infrastructure.
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- High-End: This metal-free fiber optic audio cable, featuring a fully flexible PVC jacket, is entirely immune to electrical interference. Each cable undergoes multi-stage testing during manufacturing to ensure maximum product quality and durability
- 24K gold-plated connectors: Corrosion resistant gold plating keeps connectors clean. And because these cables are fiber optic, they provide 100 % signal transmission with 0 % loss
- No risk: 36 months manufacturer warranty
What happens when a cable is damaged?
Specialist repair crews use dedicated equipment and vessels to locate and recover a damaged cable. Depending on the fault and conditions, they cut away the damaged section and join in compatible replacement cable, then test the repaired link. A repair may require extra cable; deep-sea repairs can sometimes require an added repeater to compensate for signal loss. ITU-T G.971 includes maintenance and repair guidance.
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How large is the global cable network?
Counts depend on whether they cover active cables alone or include systems still planned. The European Commission Joint Research Centre reported more than 1.3 million km of subsea cable and over 400 active cables worldwide in 2025. The ITU’s 2026 backgrounder reported over 500 active and planned telecommunication submarine cable systems as of 2024. Those figures describe different categories and dates, so they should not be read as competing counts of the same set.
A 13,000 km ocean crossing is the scale of a particular route, not the standard length of every cable system. Each route is designed for its endpoints, seabed conditions, protection needs and transmission requirements.
Quick Recap
Sources
- International Telecommunication Union, “Submarine cable resilience” (updated April 2026)
- ITU-T Recommendation G.978 (May 2025)
- ITU-T Recommendation G.971 (December 2024)
- NOAA, “Submarine Cables”
- European Commission Joint Research Centre, “Subsea cables: how vulnerable are they and can we protect them?” (8 August 2025)
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