Hokkaido-Akita Cable: connecting northern Japan
The Hokkaido-Akita Cable is a submarine telecommunications cable linking
Akita Prefecture on Japan's main island of Honshu with
Sapporo, the capital city of Hokkaido. Spanning 770 kilometers, this cable is owned jointly by four major Japanese telecom operators: KDDI, NTT, Rakuten, and Softbank. As of 2023, it is listed as in service according to GeoCables records.
What stands out about this cable is the absence of publicly disclosed technical specifications, such as its design capacity, fiber pair count, or supplier details. This lack of transparency is unusual for a cable serving a developed market like Japan, where submarine cable projects are typically well-documented. Additionally, its role in connecting two key regions of Japan raises questions about its integration with other cables in the area, such as the
Japan Information Highway (JIH) at Akita.
Quick facts
| Cable name | Hokkaido-Akita Cable |
| Length | 770 km |
| Ready for service | 2023 (GeoCables database) |
| Owners | KDDI, NTT, Rakuten, Softbank |
| Status | In service |
| Design capacity | Not disclosed |
| Fiber pairs | Not disclosed |
| Supplier | Not disclosed |
| Landing points | Akita (Japan), Sapporo (Japan) |
| Other cables at Akita | Japan Information Highway (JIH) |
Route
The Hokkaido-Akita Cable connects Akita, located on the northwest coast of Honshu, with Sapporo on Hokkaido, Japan's northernmost main island. Akita serves as a critical hub for telecommunications infrastructure, as evidenced by the presence of other cables such as the Japan Information Highway (JIH). Sapporo, on the other hand, is a major urban center and economic hub in Hokkaido, making it a logical endpoint for a cable designed to enhance connectivity between these regions.
Geographically, the cable traverses the Tsugaru Strait, a narrow body of water separating Honshu and Hokkaido. The strait's depth and geological conditions likely influenced the cable's design and installation, though specific details about its burial depth or routing are not publicly available.
Why it was built and what it carries
The Hokkaido-Akita Cable was likely built to improve telecommunications reliability and capacity between Hokkaido and Honshu. As Japan's northernmost island, Hokkaido has unique connectivity needs due to its geographic isolation and economic significance. Sapporo, in particular, is a hub for industries such as agriculture, tourism, and technology, all of which require strong data connectivity.
While the cable's design capacity is not disclosed, its ownership by four major telecom operators suggests it plays a significant role in supporting consumer internet, enterprise services, and possibly mobile network backhaul. This is consistent with industry trends in Japan, where submarine cables are integral to maintaining high-speed, low-latency connectivity across the archipelago.
History: what can be established
GeoCables records the Hokkaido-Akita Cable as having been ready for service in 2023. No conflicting dates have been identified in industry sources, so this year appears reliable. However, the absence of detailed announcements or public documentation about its construction timeline leaves gaps in understanding its development.
The involvement of KDDI, NTT, Rakuten, and Softbank suggests a collaborative approach to addressing regional connectivity needs. These companies are among Japan's largest telecom operators, each with extensive experience in submarine cable projects. Their shared ownership likely reflects the strategic importance of the cable for multiple stakeholders.
Capacity and technology
Publicly available information does not disclose the Hokkaido-Akita Cable's design capacity, fiber pair count, or supplier. Without operator documentation, attributing specific technologies or performance metrics would be speculative. Given the involvement of major telecom operators, it is reasonable to assume the cable employs modern optical technologies, but this cannot be confirmed.
Latency: the physics
The computed one-way light propagation latency over the cable's 770 km length is approximately 3.8 milliseconds, with a theoretical round-trip time (RTT) floor of about 7.5 milliseconds. This calculation assumes light travels at 200,000 to 204,000 km/s in optical fiber.
Real-world latency measurements would be higher due to additional factors such as signal processing at terminals, routing through network nodes, and the inclusion of land-based segments. No live measurements are currently available for this cable, so its actual performance remains unverified.
Redundancy: what happens if it breaks
If the Hokkaido-Akita Cable were to experience a fault, redundancy would likely be provided by other cables in the region, such as the Japan Information Highway (JIH), which also lands at Akita. Repairing submarine cables typically involves deploying specialized cable ships to locate and fix the fault, a process that can take days to weeks depending on weather, fault location, and cable complexity.
Given the cable's ownership by four major operators, it is likely that contingency plans are in place to reroute traffic through alternative infrastructure during outages. However, specific details about redundancy arrangements are not publicly available.
Bottom line
- The Hokkaido-Akita Cable spans 770 km, connecting Akita and Sapporo in northern Japan.
- It is owned by KDDI, NTT, Rakuten, and Softbank, and listed as in service since 2023.
- Design capacity, fiber pair count, and supplier details are not publicly disclosed.
- Its theoretical latency is approximately 7.5 ms RTT over the wet segment, though real-world latency is higher.
- Redundancy may be provided by the Japan Information Highway (JIH) at Akita, but specific arrangements are not documented.