Jeju-Mainland 3: A Submarine Link Between Jeju Island and the Korean Mainland
Jeju-Mainland 3 is a submarine cable connecting Jeju Island to the mainland of South Korea. Owned by KT, one of South Korea's largest telecommunications operators, the cable is listed as in service and spans 236 km. It lands at
Goseong-ri on Jeju Island and
Mijo-myeon on the mainland. While specific technical details such as design capacity, fiber pair count, and supplier are not publicly disclosed, the cable plays a role in providing connectivity between Jeju and the mainland, complementing other cables in the corridor.
What stands out about Jeju-Mainland 3 is the lack of publicly available technical data, which is unusual for submarine cables of this scale. Additionally, its recorded ready-for-service (RFS) year of 2000 is consistent with GeoCables database records, though no conflicting industry sources have surfaced to challenge this date. The cable’s role in redundancy and regional connectivity is noteworthy, as it shares landing points with other cables, including
Jeju-Mainland 2 and
Jeju-Udo.
Quick facts
| System Name | Jeju-Mainland 3 |
| Length | 236 km |
| Ready-for-Service Year | 2000 (GeoCables database) |
| Owner | KT |
| Status | In service |
| Design Capacity | Not disclosed |
| Fiber Pairs | Not disclosed |
| Supplier | Not disclosed |
| Technology | Not disclosed |
| Landing Points | Goseong-ri (South Korea); Mijo-myeon (South Korea) |
Route
Jeju-Mainland 3 connects Goseong-ri on Jeju Island to Mijo-myeon on the mainland of South Korea. Goseong-ri is a key landing site on Jeju Island, hosting other cables such as Jeju-Mainland 2 and Jeju-Udo. Mijo-myeon, located on the southern coast of the mainland, serves as the mainland landing point. The route spans 236 km undersea, traversing the Korea Strait, which separates Jeju Island from the mainland.
Why it was built and what it carries
Jeju-Mainland 3 was built to enhance connectivity between Jeju Island and the mainland of South Korea, ensuring reliable communication for residents, businesses, and government operations. Jeju Island is a popular tourist destination and a growing economic hub, making strong telecommunications infrastructure essential. While the cable's specific data transmission capacity is not disclosed, it likely supports internet traffic, voice communications, and other data services.
The cable complements other systems in the corridor, such as Jeju-Mainland 2, providing redundancy and additional bandwidth. Its importance lies in maintaining connectivity in a region prone to weather-related disruptions and high data demand.
History: what can be established
According to GeoCables records, Jeju-Mainland 3 became ready for service in 2000. No conflicting industry sources have been identified, so this date is assumed accurate. KT, the cable's owner, has a long history of operating submarine cables in South Korea, and Jeju-Mainland 3 is part of a family of systems that includes Jeju-Mainland 2.
Publicly available information about the cable's construction, supplier, and initial deployment is scarce, which is not uncommon for older submarine cables in regional corridors.
Capacity and technology
The design capacity, fiber pair count, and specific technology used in Jeju-Mainland 3 are not disclosed in public sources. Without operator documentation, it is impossible to state these parameters. Given its RFS year of 2000, the cable likely uses technology typical of that era, but attributing specific details would be speculative.
Latency: the physics
The theoretical one-way light propagation time over the 236 km wet segment of Jeju-Mainland 3 is approximately 1.2 ms, assuming light travels at 200,000 to 204,000 km/s in optical fiber. The theoretical round-trip time (RTT) for the wet segment is about 2.3 ms. However, real-world latency is higher due to land tails, terminal equipment, and routing inefficiencies. No live latency measurements for Jeju-Mainland 3 are currently available, and any estimates beyond the theoretical floor would require direct testing.
Redundancy: what happens if it breaks
Jeju-Mainland 3 shares landing points at Goseong-ri with Jeju-Mainland 2 and Jeju-Udo, providing redundancy in the corridor. If the cable were to break, traffic could potentially be rerouted through these alternative systems, minimizing disruption. Repairing submarine cables typically involves locating the fault using underwater survey techniques, deploying cable ships, and splicing or replacing the damaged section. The Korea Strait is a relatively shallow water body, which may simplify repair operations compared to deeper oceanic environments.
Bottom line
- Jeju-Mainland 3 is a submarine cable connecting Jeju Island to the South Korean mainland, spanning 236 km.
- Owned by KT, it has been in service since 2000 according to GeoCables records.
- Technical details such as design capacity, fiber pairs, and supplier are not publicly disclosed.
- The cable shares landing points with Jeju-Mainland 2 and Jeju-Udo, providing redundancy in the corridor.
- Theoretical latency over the wet segment is approximately 2.3 ms RTT, though real-world latency is higher.
- Public information about its construction and deployment is limited.