Jeju-Udo: A Short Submarine Cable Linking Two South Korean Islands
The Jeju-Udo submarine cable connects
Goseong-ri on Jeju Island to Udo, a smaller island off the eastern coast of Jeju. At just 3 kilometers in length, it is among the shortest submarine cables in operation, designed to provide reliable connectivity between these two islands. The cable is owned by four major South Korean telecom operators: KCTV Jeju Broadcasting, KT, LG Uplus, and SK Telecom (SKT), reflecting a collaborative approach to regional connectivity.
What makes this cable particularly interesting is its simplicity and localized focus. Unlike transoceanic cables that span thousands of kilometers and connect continents, Jeju-Udo serves a very specific regional need. However, much about its technical specifications, such as design capacity, fiber pairs, supplier, and technology, remains undisclosed in public sources, leaving room for speculation and highlighting the limited transparency around smaller-scale submarine projects.
Quick facts
| Cable name | Jeju-Udo |
| Length | 3 km |
| Ready-for-service year | 2023 (GeoCables database value; conflicting data not surfaced) |
| Owners | KCTV Jeju Broadcasting, KT, LG Uplus, SK Telecom (SKT) |
| Status | In service |
| Design capacity | Not disclosed |
| Fiber pairs | Not disclosed |
| Supplier | Not disclosed |
| Technology | Not disclosed |
| Landing points | Goseong-ri (South Korea); Udo (South Korea) |
| Other cables at Goseong-ri | Jeju-Mainland 2, Jeju-Mainland 3 |
🗺 Show Jeju-Udo on the interactive cable map
Route
The Jeju-Udo cable runs between Goseong-ri, located on the northeastern coast of Jeju Island, and Udo, a small island just east of Jeju. This corridor spans only 3 kilometers across shallow waters, making it one of the shortest submarine cable routes globally. Both landing points are situated within South Korea, and the cable serves as a direct link to enhance connectivity between these two islands. Goseong-ri is also a landing site for two larger cables, Jeju-Mainland 2 and Jeju-Mainland 3, which connect Jeju Island to the South Korean mainland.
Why it was built and what it carries
The Jeju-Udo cable was likely built to meet localized connectivity needs between Jeju and Udo, such as internet access, telecommunication services, and potentially broadcasting. Udo is a popular tourist destination known for its scenic landscapes and cultural significance, and the cable likely supports both residential and commercial connectivity on the island. While specific details regarding its data transmission capacity are not disclosed, its short length and regional focus suggest it is designed for moderate traffic rather than high-capacity international data transmission.
History: what can be established
The GeoCables database records the Jeju-Udo cable as ready for service in 2023. No conflicting industry sources have surfaced to suggest a different year, so this date is taken as accurate. The cable's ownership by four major telecom operators indicates a collaborative effort to address regional connectivity needs, but further details about its construction timeline, supplier, and deployment logistics are not publicly available.
Capacity and technology
Publicly available data does not disclose the design capacity, fiber pairs, supplier, or specific technology used in the Jeju-Udo cable. Without operator documentation, attributing these characteristics would be speculative. Given its short length and regional focus, it is reasonable to assume the cable employs standard submarine cable technology suitable for shallow water and moderate traffic, but this cannot be confirmed without further information.
Latency: the physics
The theoretical one-way light propagation latency over the 3-kilometer wet segment of the Jeju-Udo cable is approximately 0.0 milliseconds, assuming light travels at speeds between 200,000 and 204,000 kilometers per second in optical fiber. The round-trip time (RTT) for the wet segment is similarly negligible, at approximately 0.0 milliseconds. However, real-world latency measurements would be higher due to additional factors such as signal processing in terminal equipment, routing through land tails, and network congestion. No live measurements for this cable are currently available.
Redundancy: what happens if it breaks
In the event of a failure, redundancy for connectivity between Jeju and Udo would likely depend on terrestrial wireless networks or other localized solutions, as no alternative submarine cables directly connect these two islands. However, Goseong-ri serves as a landing point for Jeju-Mainland 2 and Jeju-Mainland 3, which connect Jeju Island to the mainland. These cables could provide indirect redundancy for broader connectivity needs involving Jeju.
Repairing a cable as short as Jeju-Udo would likely involve standard industry practices, including deploying cable repair ships equipped with remotely operated vehicles (ROVs) for shallow-water operations. Given the cable's proximity to shore and its short length, repairs would likely be faster and less complex than for longer, deep-water cables.
Bottom line
- The Jeju-Udo submarine cable spans 3 kilometers, connecting Goseong-ri on Jeju Island to Udo, South Korea.
- It is owned by KCTV Jeju Broadcasting, KT, LG Uplus, and SK Telecom (SKT).
- Ready-for-service year is recorded as 2023, with no conflicting data identified.
- Design capacity, fiber pairs, supplier, and technology are not disclosed in public sources.
- Theoretical latency over the wet segment is negligible, but real-world RTT would be higher.
- Redundancy options are limited to terrestrial networks or indirect routes via other cables landing at Goseong-ri.