Jeju-Mainland 2: A submarine cable connecting South Korea's mainland to Jeju Island
The Jeju-Mainland 2 submarine cable is a repeatered fiber optic system linking the South Korean mainland at
Goheung to Jeju Island at
Goseong-ri. Owned by KT, one of South Korea's major telecommunications operators, the cable has been in service since 1996 according to GeoCables records. Its primary role is to support telecommunications traffic between Jeju Island and the mainland, complementing other cables in the corridor such as
Jeju-Mainland 3 and
Jeju-Udo.
What makes Jeju-Mainland 2 particularly interesting is the limited public disclosure regarding its technical specifications, including design capacity and fiber pair count. While the supplier is most likely LS Cable & System, this attribution remains unconfirmed without operator documentation. The cable employs SDH/SONET technology, a standard for synchronous optical networking, and includes repeaters to amplify the signal over its 191 km length.
Quick facts
| Length | 191 km |
| Ready-for-service year | 1996 (GeoCables database) |
| Owners | KT |
| Status | In service |
| Design capacity | Not disclosed |
| Fiber pairs | Not disclosed |
| Supplier | LS Cable & System (probable) |
| Technology | SDH/SONET, Repeatered |
| Landing points | Goheung (South Korea); Goseong-ri (South Korea) |
| Other cables at Goseong-ri | Jeju-Mainland 3, Jeju-Udo |
| Same-family systems | Jeju-Mainland 3 |
🗺 Show Jeju-Mainland 2 on the interactive cable map
Route
The cable connects Goheung on the South Korean mainland to Goseong-ri on Jeju Island. Both landing points are strategically located to facilitate reliable connectivity between the island and the mainland. Jeju Island, a popular tourist destination and a growing economic hub, relies on submarine cables like Jeju-Mainland 2 to ensure uninterrupted communication and data transfer.
Why it was built and what it carries
Jeju-Mainland 2 was built to strengthen telecommunications infrastructure between Jeju Island and the mainland, addressing the increasing demand for connectivity in the region. Jeju Island's economic development, tourism, and growing population have made reliable communication channels essential. The cable likely carries internet, voice, and data traffic, although specific details about its traffic composition are not publicly disclosed.
History: what can be established
GeoCables records indicate that Jeju-Mainland 2 was ready for service in 1996. Publicly available data does not suggest any alternative commissioning year, nor does it provide insight into significant upgrades or changes since its deployment. The cable's ownership by KT aligns with the company's role as a major telecom operator in South Korea.
Capacity and technology
The design capacity of Jeju-Mainland 2 is not disclosed in public sources, nor is the number of fiber pairs it contains. The cable uses SDH/SONET technology, which was widely adopted in the 1990s for its ability to provide synchronized data transmission. Repeaters are used along the cable's 191 km length to maintain signal strength, a standard practice for repeatered systems.
Latency: the physics
The computed one-way light propagation latency over the 191 km wet segment is approximately 0.9 ms, while the theoretical round-trip time (RTT) floor is around 1.9 ms. Real-world latency measurements, however, are higher due to additional delays introduced by land tails, terminal equipment, and routing. For example, GeoCables live measurements show RTTs of 311.2 ms from Almaty to Goheung, 69.3 ms from Singapore to Goheung, and 283.4 ms from Sao Paulo to Goheung. These values reflect the full internet path, not the cable itself.
Redundancy: what happens if it breaks
In the event of a failure, redundancy is provided by other cables in the corridor, such as Jeju-Mainland 3 and Jeju-Udo, which also land at Goseong-ri. Repairing submarine cables typically involves deploying specialized cable ships to locate, retrieve, and fix the damaged section. Given the relatively short length of Jeju-Mainland 2, repair operations would likely be less complex compared to longer transoceanic systems.
Bottom line
- Jeju-Mainland 2 is a repeatered submarine cable connecting Goheung and Goseong-ri in South Korea.
- Owned by KT, it has been in service since 1996 according to GeoCables records.
- Key technical details like design capacity and fiber pairs are not publicly disclosed.
- Its computed one-way latency is approximately 0.9 ms, with real-world RTTs reflecting broader internet paths.
- Redundancy is provided by other cables in the corridor, such as Jeju-Mainland 3 and Jeju-Udo.