Japan Information Highway (JIH)

Japan Information Highway (JIH): A domestic submarine cable system in Japan

The Japan Information Highway (JIH) is a submarine cable system spanning 5,150 kilometers, designed to connect multiple landing points across Japan. Owned by KDDI, one of Japan's leading telecommunications providers, the cable has been operational since 1999 according to GeoCables records. It serves as an important domestic infrastructure, linking key regions and cities with high-speed connectivity. While the cable's geographical scope and landing points are well-documented, several technical details remain undisclosed in public sources. The design capacity, number of fiber pairs, supplier, and specific technological configurations have not been published, leaving room for speculation about its exact capabilities. This lack of transparency is not uncommon in older cable systems, especially those that primarily serve domestic routes rather than international corridors.

Quick facts

System Name	Japan Information Highway (JIH)
Length	5150 km
Ready-for-Service (RFS) Year	1999 (GeoCables database)
Owner	KDDI
Status	In service
Design Capacity	Not disclosed
Fiber Pairs	Not disclosed
Supplier	Not disclosed
Technology	Not disclosed
Landing Points	Akita, Chikura, Ibaraki, Ishikari, Miyazaki, Naha, Ninomiya, Sendai, Shima

Show Japan Information Highway (JIH) on the interactive cable map

Route

The JIH connects nine landing points across Japan: Akita, Chikura, Ibaraki, Ishikari, Miyazaki, Naha, Ninomiya, Sendai, and Shima. These locations span Japan's main islands, including Honshu, Hokkaido, Kyushu, and Okinawa, ensuring comprehensive coverage of the country. The cable's route reflects Japan's need for reliable domestic connectivity between major urban centers and regional hubs.

Why it was built and what it carries

The Japan Information Highway was built to support Japan's growing demand for domestic telecommunications infrastructure in the late 1990s. As Japan's economy and internet usage expanded, the need for reliable, high-capacity connectivity between different parts of the country became apparent. The cable most likely facilitates a mix of internet traffic, private network connectivity, and domestic data exchange, although specific details about its traffic composition are not publicly disclosed.

History: what can be established

GeoCables records indicate that the JIH entered service in 1999. However, no conflicting dates have been identified in industry sources, suggesting general agreement on its operational timeline. The cable's construction coincided with a period of rapid growth in Japan's telecommunications sector, driven by increasing internet penetration and the rise of broadband technologies.

Capacity and technology

The design capacity, fiber count, supplier, and underlying technology of the Japan Information Highway have not been disclosed in public sources. Without operator documentation, it is impossible to attribute specific figures or technological features to the cable. Given its age, the JIH likely uses older optical transmission technologies compared to modern systems, but this cannot be confirmed without further information.

Latency: the physics

The theoretical one-way light propagation latency over the JIH's 5,150 km length is approximately 25.2 milliseconds, with a round-trip time (RTT) floor of 50.5 milliseconds. These calculations assume ideal conditions, such as light traveling at 200,000 to 204,000 km/s in fiber. Real-world latency measurements, however, are higher due to factors like land tails, terminal equipment, and routing inefficiencies. Live measurements from remote probes show significantly higher RTTs for paths involving Ibaraki, one of JIH's landing points. For example:

• Almaty -> Ibaraki: 320.7 ms
• Singapore -> Ibaraki: 94.4 ms
• Moscow -> Ibaraki: 264.5 ms
• Sao Paulo -> Ibaraki: 319.3 ms

These figures reflect the latency of the entire internet path, not the JIH cable itself, and include delays from terrestrial networks and intermediate routing.

Redundancy: what happens if it breaks

The JIH's landing points are served by multiple other submarine cables, providing redundancy in case of outages. For example:

• Akita: Hokkaido-Akita Cable
• Chikura: APCN-2, EAC-C2C, FASTER, Southeast Asia-Japan Cable (SJC), Unity
• Ishikari: Hokkaido-Sakhalin Cable System (HSCS)
• Miyazaki: Miyazaki-Okinawa Cable (MOC)
• Naha: Guam Okinawa Kyushu Incheon (GOKI), YUI
• Shima: Asia Pacific Gateway (APG), Australia-Japan Cable (AJC), JUNO

These alternative systems reduce the risk of service disruption, particularly for international traffic that might transit through Japan.

Bottom line

• The Japan Information Highway (JIH) spans 5,150 km and connects nine landing points across Japan.
• Owned by KDDI, the cable has been in service since 1999 according to GeoCables records.
• Technical details such as design capacity, fiber pairs, and supplier are not publicly disclosed.
• Theoretical latency over the cable is approximately 25.2 ms one-way, but real-world measurements reflect higher values due to network factors.
• Redundancy is provided by multiple other cables serving the same landing points.