Hosan-ri, South Korea: no other cable lands within 50 km.
Ulleung, South Korea: no other cable lands within 50 km.
On an island this means losing the submarine link; on the mainland traffic can still go over land.
Our alerts on this cable in the last 180 days: 6, last on 29 Sep 2026. Events feed →
Counted: other international cables landing in the same country (domestic cables between points of one country are not a way out), other cables at landing points within 50 km, and whether the country has land links. Not counted: cable capacity, operator contracts and satellite. Use as a first look at dependence, not as a statement of what would happen.
Live Performance
304
measurements
15
probes
72
days monitored
325.8
ms avg RTT
6
anomalies
Monitored from 2026-07-19 through 2026-09-29 - live ICMP round-trip time measurements via our monitoring probes. All values below are recomputed daily from raw probe data.
Measurement sources
Probe
Location
Samples
Avg
Min-Max
Last seen
own probe
Almaty KZ
33
344.0 ms
309.6-452.8
2026-09-29
#6410 own probe
Sao Paulo BR
26
319.8 ms
302.7-330.8
2026-09-29
own probe
Moscow RU
23
273.3 ms
183.6-307.5
2026-09-29
#6427 own probe
Sydney AU
22
298.4 ms
285.5-302.6
2026-09-29
#7062 own probe
Cape Town ZA
22
412.6 ms
367.2-428.9
2026-09-29
own probe
Minsk BY
22
375.8 ms
249.4-417.3
2026-09-29
own probe
Tbilisi GE
22
334.2 ms
317.5-349.7
2026-09-29
own probe
Sevastopol UA
22
298.5 ms
205.7-332.0
2026-09-29
own probe
Odessa UA
22
305.2 ms
260.2-326.6
2026-09-29
own probe
Kyiv UA
22
314.4 ms
302.3-324.2
2026-09-29
own probe
Jerusalem IL
17
319.2 ms
286.0-336.7
2026-09-29
own probe
Saint Petersburg RU
17
316.7 ms
184.9-413.5
2026-09-29
own probe
Balancer IL
17
327.4 ms
290.9-337.9
2026-09-29
own probe
Rostov RU
15
337.6 ms
326.2-339.0
2026-09-26
#6487
control probe
2
99.4 ms
99.4-99.5
2026-08-17
About the Ulleung-Mainland 2 Cable System
Ulleung-Mainland 2: Connecting South Korea's mainland to Ulleung Island
The Ulleung-Mainland 2 submarine cable is a fiber-optic telecommunications link spanning 164 kilometers, connecting Hosan-ri on South Korea's mainland to Ulleung Island. Owned and operated by KT, this cable is listed as in service and was recorded as ready for service in 2016 according to the GeoCables database. Its purpose is to provide reliable connectivity to Ulleung Island, a remote location in the East Sea (Sea of Japan), ensuring reliable communication and internet services for residents and businesses.
What makes the Ulleung-Mainland 2 cable particularly interesting is the lack of publicly disclosed technical details, such as its design capacity, fiber pair count, supplier, and specific technology. This absence of information reflects the relatively low-profile nature of regional submarine cables that serve smaller, localized markets. Additionally, while the cable's latency floor can be calculated based on its length, real-world performance data is not currently available, leaving some aspects of its operational characteristics unverified.
The Ulleung-Mainland 2 cable connects Hosan-ri, a coastal area on South Korea's eastern mainland, to Ulleung Island, a volcanic island located approximately 164 kilometers offshore in the East Sea (Sea of Japan). Ulleung Island is known for its rugged terrain and sparse population, making reliable telecommunications infrastructure essential for its residents and visitors. This cable provides a direct link between the island and the mainland, bypassing the need for satellite connectivity, which is typically slower and less reliable.
Why it was built and what it carries
The primary purpose of the Ulleung-Mainland 2 cable is to ensure stable and high-speed communication for Ulleung Island, which relies heavily on such infrastructure due to its geographic isolation. Submarine cables like this are essential for delivering internet, voice, and data services to remote locations. While specific details about the cable's capacity and usage are not disclosed, it is reasonable to assume that it supports both residential and commercial telecommunications needs, as well as government and emergency services.
History: what can be established
The GeoCables database records the Ulleung-Mainland 2 cable as ready for service in 2016. No conflicting dates have been identified in industry sources, so this timeline appears consistent. The cable's deployment likely involved standard industry practices, including seabed surveys, cable laying, and burial where necessary to protect against environmental hazards and fishing activity. However, without public documentation, details about the construction process and challenges remain unknown.
Capacity and technology
Publicly available data does not disclose the design capacity, fiber pair count, supplier, or technology used in the Ulleung-Mainland 2 cable. These parameters are typically proprietary for regional cables serving smaller markets, where competitive pressures and regulatory requirements may not mandate transparency. As a result, attributing specific technical characteristics to this cable without operator documentation would be speculative.
Latency: the physics
The computed one-way light propagation latency for the Ulleung-Mainland 2 cable is approximately 0.8 milliseconds, based on its 164-kilometer length and the speed of light in fiber (200,000 to 204,000 km/s). This yields a theoretical round-trip time (RTT) floor of 1.6 milliseconds over the wet segment. However, real-world latency is higher due to additional factors such as land tails, terminal equipment, and network routing. Since no live measurements are currently available for this cable, its actual performance remains unverified.
Redundancy: what happens if it breaks
In the event of a failure, redundancy for the Ulleung-Mainland 2 cable would depend on alternative connectivity options for Ulleung Island. These could include satellite links or older submarine cables, though their capacity and reliability may not match that of the Ulleung-Mainland 2. Repairing a submarine cable typically involves deploying specialized cable ships to locate and fix the fault, which can be time-consuming depending on weather conditions and the nature of the damage. Given the cable's relatively short length, repairs may be logistically simpler compared to longer transoceanic systems.
Bottom line
The Ulleung-Mainland 2 cable spans 164 kilometers, connecting Hosan-ri to Ulleung Island in South Korea.
Owned by KT, it was recorded as ready for service in 2016 and is listed as in service.
Technical details such as design capacity, fiber pairs, supplier, and technology are not publicly disclosed.
Computed latency is approximately 0.8 ms one-way, with a theoretical RTT floor of 1.6 ms over the wet segment.
Redundancy options for Ulleung Island may include satellite links or older cables, but specifics are unclear.