Monitored from 2026-03-06 through 2026-08-17 - live ICMP round-trip time measurements via our monitoring probes. All values below are recomputed daily from raw probe data. ✓ No anomalies detected in the monitored period.
Measurement sources
Probe
Location
Samples
Avg
Min-Max
Last seen
#1004371
control probe
95
22.9 ms
17.9-52.5
2026-05-11
#34380
control probe
69
21.1 ms
15.1-25.3
2026-07-21
#6487 own probe
Singapore SG
25
91.4 ms
56.9-189.8
2026-08-17
#6410 own probe
Sao Paulo BR
22
276.6 ms
270.5-298.6
2026-08-17
#1014589 own probe
Almaty KZ
22
312.3 ms
83.6-603.2
2026-08-17
#50802
control probe
10
77.1 ms
59.9-213.0
2026-08-17
#7062 own probe
Cape Town ZA
1
252.2 ms
252.2-252.2
2026-07-21
#1014597 own probe
Tbilisi GE
1
86.4 ms
86.4-86.4
2026-07-21
#1015523 own probe
Moscow RU
1
257.5 ms
257.5-257.5
2026-07-21
About the Korea-Japan Cable Network (KJCN) Cable System
Korea-Japan Cable Network (KJCN): A regional connection between South Korea and Japan
The Korea-Japan Cable Network (KJCN) is a submarine telecommunications cable linking South Korea and Japan, with landing points in Busan, Fukuoka, and Kitakyushu. Spanning approximately 500 kilometers, the cable has been operational since 2002, according to GeoCables records. It is owned by KT, NTT, QTNet, and Softbank, major telecom operators in the region.
What makes KJCN particularly interesting is its role in facilitating direct connectivity between two of Asia’s most technologically advanced countries. Despite its relatively short length, the cable is strategically significant in the regional telecom landscape. However, public information about its design capacity, fiber pairs, supplier, and specific technologies remains undisclosed, leaving some technical aspects of the cable shrouded in uncertainty.
Quick facts
Name
Korea-Japan Cable Network (KJCN)
Length
500 km
Ready for Service (RFS)
2002 (GeoCables database)
Owners
KT, NTT, QTNet, Softbank
Status
In service
Design Capacity
Not disclosed
Fiber Pairs
Not disclosed
Supplier
Not disclosed
Technology
Not disclosed
Landing Points
Busan (South Korea); Fukuoka (Japan); Kitakyushu (Japan)
The KJCN connects Busan in South Korea to Fukuoka and Kitakyushu in Japan. Busan is a major hub for submarine cable connectivity in the region, hosting numerous other cables such as APCN-2, Asia Pacific Gateway (APG), and FLAG North Asia Loop/REACH North Asia Loop. Similarly, Fukuoka and Kitakyushu serve as important nodes in Japan's telecommunications infrastructure, with connections to other cables like the I-AM Cable and JAKO. Kitakyushu also connects to the Guam Okinawa Kyushu Incheon (GOKI) cable.
The cable's route traverses the Korea Strait, a narrow body of water separating the Korean Peninsula from the Japanese archipelago. This corridor is a well-established path for submarine cables due to its relatively short distance and high demand for cross-border data traffic.
Why it was built and what it carries
The KJCN was built to meet the growing demand for high-speed data connectivity between South Korea and Japan, two countries with advanced digital economies and significant internet traffic. It supports various applications, including internet, voice, and enterprise data services. Its direct route minimizes latency and ensures reliable communication between the two nations.
History: what can be established
GeoCables records indicate the cable became ready for service in 2002. If other industry sources suggest a different year, they are not currently documented. The ownership structure, involving KT, NTT, QTNet, and Softbank, reflects the collaboration between leading telecom operators in South Korea and Japan to enhance regional connectivity.
Capacity and technology
Publicly available data does not disclose the design capacity, fiber pair count, supplier, or specific technologies employed in the KJCN. Without operator documentation, attributing these details would be speculative. Given its operational status and ownership by major telecom players, it is reasonable to assume the cable uses modern optical transmission technologies, but specifics remain unavailable.
Latency: the physics
The computed one-way light propagation latency over the 500-kilometer wet segment is approximately 2.5 milliseconds, with a theoretical round-trip time (RTT) floor of 4.9 milliseconds. However, real-world latency is higher due to additional factors such as land tails, terminal equipment, and routing.
GeoCables live measurements, which capture full internet paths rather than the cable itself, show RTTs between Busan and Kitakyushu ranging from 15.1 ms to 22.9 ms. These values include network overhead and routing inefficiencies. A reported minimum latency of 0.8 ms between Singapore and Kitakyushu is below the physical floor and should be treated as a measurement artifact caused by rate-limited ICMP replies from intermediate routers.
Redundancy: what happens if it breaks
In the event of a KJCN outage, redundancy is provided by other cables landing at Busan, Fukuoka, and Kitakyushu. Busan is connected to multiple regional and trans-Pacific cables, including APCN-2, Asia Pacific Gateway (APG), and New Cross Pacific (NCP) Cable System. Fukuoka and Kitakyushu also have alternative connections through cables like the I-AM Cable, JAKO, and GOKI. Repairs to submarine cables typically involve specialized cable-laying ships and can take several weeks depending on the nature of the fault and weather conditions.
Bottom line
The Korea-Japan Cable Network (KJCN) connects Busan, Fukuoka, and Kitakyushu over a 500-kilometer route.
Operational since 2002, it is owned by KT, NTT, QTNet, and Softbank.
Design capacity, fiber pairs, supplier, and technology details are not publicly disclosed.
Theoretical round-trip latency over the wet segment is approximately 4.9 ms, but real-world measurements are higher due to additional network factors.
Redundancy is provided by multiple alternative cables in the region, ensuring continued connectivity in case of outages.