Russia-Japan Cable Network (RJCN)

Russia-Japan Cable Network (RJCN): A submarine link between two nations

The Russia-Japan Cable Network (RJCN) is a submarine telecommunications cable connecting Joetsu, Japan, and Nahodka, Russia. Stretching approximately 1800 kilometers across the Sea of Japan, this cable facilitates data exchange between two geographically close but geopolitically distinct regions. Owned jointly by KDDI of Japan and Rostelecom of Russia, the RJCN is listed as in service and has been operational since 2008, according to GeoCables records. What makes RJCN particularly noteworthy is the limited public disclosure regarding its technical specifications, such as design capacity, fiber pair count, and supplier information. This lack of transparency is not uncommon in the submarine cable industry, especially for cables serving sensitive geopolitical corridors. Furthermore, live latency measurements reveal a significant discrepancy between theoretical and observed performance, raising questions about the cable's configuration and broader network routing.

Quick facts

Cable name	Russia-Japan Cable Network (RJCN)
Length	1800 km
Ready for service (RFS)	2008 (GeoCables database value)
Owners	KDDI, Rostelecom
Status	In service
Design capacity	Not disclosed
Fiber pairs	Not disclosed
Supplier	Not disclosed
Technology	Not disclosed
Landing points	Joetsu (Japan), Nahodka (Russia)
Other cables at Nahodka	Polar Express

Route

The RJCN connects Joetsu on Japan’s western coast to Nahodka, a port city in Russia’s Far East. Both landing points are strategically positioned for intercontinental data exchange, with Joetsu serving as a hub for Japanese telecommunications and Nahodka providing access to Russia's vast terrestrial network infrastructure. The cable traverses the Sea of Japan, a maritime region known for its challenging weather conditions and variable seabed topography.

Why it was built and what it carries

The RJCN was built to enhance connectivity between Japan and Russia, two nations with growing economic and technological ties. By providing a direct submarine link, the cable reduces reliance on longer terrestrial routes through third countries. It is likely used to carry a mix of internet traffic, enterprise data, and possibly government communications, although specific usage patterns are not publicly detailed.

History: what can be established

GeoCables database records state that the RJCN was ready for service in 2008. No conflicting dates have been identified in publicly available industry sources, suggesting that this timeline is accurate. However, the lack of detailed historical documentation about the cable's construction and commissioning limits further analysis of its development process.

Capacity and technology

Publicly available data does not disclose the cable's design capacity, number of fiber pairs, or the specific technology employed. Without operator documentation, it is impossible to determine these parameters. It is reasonable to assume that the cable uses industry-standard optical fiber technology for high-speed data transmission, but attributing specific capabilities would be speculative.

Latency: the physics

Theoretical one-way light propagation over the 1800 km wet segment of the RJCN is approximately 8.8 milliseconds, resulting in a round-trip time (RTT) floor of 17.6 milliseconds. However, live measurements from remote probes show significantly higher RTTs:

• Joetsu -> Nahodka: minimum 39.1 ms, average 43.5 ms
• Nahodka -> Joetsu: minimum 40.7 ms, average 106.6 ms

These discrepancies can be attributed to additional latency introduced by land-based network tails, terminal equipment, and routing inefficiencies beyond the cable itself. The asymmetry in RTT between directions may reflect differences in routing paths or network congestion.

Redundancy: what happens if it breaks

In the event of a failure, redundancy for the RJCN could be provided by other cables landing at Nahodka, such as the Polar Express. However, alternative routes would likely involve longer paths through terrestrial networks or other submarine cables, potentially increasing latency. Repair logistics for submarine cables typically involve specialized cable ships equipped to locate, retrieve, and repair damaged sections, a process that can take weeks depending on the location and severity of the fault.

Bottom line

• The RJCN is a 1800 km submarine cable connecting Joetsu, Japan, and Nahodka, Russia.
• Operational since 2008, it is owned by KDDI and Rostelecom.
• Technical specifications such as design capacity and fiber pairs are not publicly disclosed.
• Theoretical latency is approximately 17.6 ms RTT over the wet segment, but live measurements show higher values due to additional network factors.
• Redundancy options include the Polar Express cable, but failure recovery could be time-consuming.