Guam Okinawa Kyushu Incheon (GOKI)

GOKI: A Cable Built from the Legacy of the First Trans-Pacific Era

GOKI is a unique regional submarine cable connecting Guam with Japan's Okinawa and Kyushu islands. It spans approximately 4,244 km, is owned and operated by AT&T, and has active landing points at Tumon Bay in Guam, Naha in Okinawa, and the Kitakyushu area in Kyushu.

At first glance, GOKI appears to be a typical cable system built in the early 2010s to connect Guam with Japan. However, its history is far more intriguing. The system was constructed using resources from the decommissioned TPC-5 cable, equipped with new optical technology from Xtera, and retained a name referencing South Korea's Incheon, despite having no confirmed landing point in South Korea.

Thus, GOKI is not just another regional cable. It serves as an example of how older oceanic infrastructure can be partially recovered, retrofitted, and repurposed into a new system.

Key Facts

🗺 Show Guam Okinawa Kyushu Incheon (GOKI) on the interactive cable map

A Name That Doesn't Match the Current Route

The name GOKI is derived from four geographic locations: Guam, Okinawa, Kyushu, and Incheon. However, the modern map of the system shows only three landing points across two territories: Guam and Japan. South Korea is absent from the list of active landing points.

Historical records indicate that a branch or extension to Incheon was indeed considered in the original concept. However, the deployed configuration does not confirm the South Korean segment. The project name remained unchanged, even though the actual route turned out to be shorter than initially planned.

This situation is not unique in the submarine cable industry. Cable names are often finalized during the early stages of planning, when the project includes more countries and branches. If one participant withdraws, fails to obtain permissions, or delays investments, the system's name is not always updated. Therefore, describing GOKI as a cable connecting Guam, Japan, and South Korea is incorrect: the confirmed operational system connects Guam, Okinawa, and Kyushu.

The History Begins with TPC-5

The most fascinating part of GOKI's story is its connection to the TPC-5 cable-Trans-Pacific Cable 5. TPC-5 belonged to a previous generation of trans-Pacific infrastructure. After its commercial operation ended, some of its submarine resources were not simply abandoned on the ocean floor. AT&T utilized suitable segments to create a new regional system.

This approach sets GOKI apart from most new cables. Typically, operators order new optical fiber, new repeaters, new branching units, complete marine installation, and the construction of new shore landings. In the case of GOKI, parts of the existing infrastructure were retrieved, inspected, modified, and re-laid. This approach is known as cable recovery and relaying.

The economic rationale is clear. Manufacturing and laying thousands of kilometers of new deep-sea cable require significant investment and specialized vessels. If an old cable is physically functional, suitable segments can still be valuable assets even after the original system ceases operation.

However, reuse does not mean that the entire GOKI system is an unchanged fragment of TPC-5. The new system required surveys, recovery, topology modifications, section connections, new terminal equipment, and re-testing.

Who Built GOKI

AT&T selected two specialized companies for the project: Xtera Communications for the optical transmission system and Kokusai Cable Ship (KCS) for marine operations and cable handling. Xtera provided DWDM equipment, while Kokusai Cable Ship carried out the recovery and re-laying of the relevant submarine segments.

There is no comprehensive technical specification of the system available in the public domain: the exact number of fiber pairs, repeater configuration, optical budget, and final capacity after potential upgrades remain unknown. However, the suppliers and initial DWDM equipment are documented.

What Is Known About Capacity

In its early configuration, Xtera specified eight optical channels of 10 Gbps each. This translates to approximately 80 Gbps of known initial equipped capacity. Some catalogs, therefore, list the design capacity as 0.08 Tbps.

However, care must be taken when using the term "design capacity." Eight channels of 10 Gbps may describe the initially installed equipment, the first commercially activated set of wavelengths, the equipment of a specific segment, or the baseline configuration at launch. This does not necessarily represent the absolute physical limit of the fiber.

Submarine cables are often upgraded by replacing terrestrial terminal equipment. If the fiber characteristics, repeaters, and optical budget allow, operators can switch from 10G to more efficient transmission formats without replacing the cable on the seabed. Therefore, the correct statement is: historical data indicates an initial configuration of eight channels at 10 Gbps, approximately 80 Gbps; the maximum physical and currently activated capacity of GOKI is not publicly confirmed.

For comparison, 80 Gbps seems modest compared to modern systems with design capacities in the hundreds of terabits. However, GOKI should not be evaluated solely by contemporary standards. It is a specialized regional route, partially built on older infrastructure and intended not to replace all trans-Pacific systems but to connect specific AT&T nodes.

Disputed Commissioning Date

GeoCables and several modern cable catalogs list GOKI's commissioning year as 2013. At the same time, historical project descriptions claim the system was approved by the U.S. regulator in 2011 but was only operational by 2017. Thus, it cannot be definitively stated that there are no discrepancies in the dates.

Several explanations are possible: 2013 might refer to the initial readiness of part of the system; 2017 might mark the completion of final reconfiguration or commercial activation; different segments might have been commissioned in phases; catalogs might have used a planned RFS as the actual date; historical sources might have referenced the latest commissioning of an updated configuration.

Without AT&T's original acceptance documentation, it is impossible to definitively choose one date. The correct statement is: modern cable databases list an RFS of 2013, but historical project materials cite 2017 as the actual commissioning date.

Why the Route Includes Okinawa

GOKI connects Guam not only with Japan's main islands but also with Okinawa. This is significant because the Japanese archipelago is a long chain of islands. Okinawa is located significantly south of Kyushu and serves as a natural intermediary node between Japan, Taiwan, the East China Sea, and the western Pacific.

Landing at Naha enables Okinawa to connect directly to an international route, transmit traffic between Guam and Japan through a separate island point, create an additional path to Japan's national network, reduce Okinawa's dependence on a single domestic direction, and utilize the island as an intermediate telecommunications hub.

However, having two Japanese points does not prove complete physical redundancy. If both branches share a common deep-sea segment to Guam, damage to the shared trunk will disable both Japanese directions simultaneously.

Kitakyushu or Fukutsu

In modern databases, GOKI's northern Japanese landing point is listed as Kitakyushu. Historical materials sometimes refer to Fukutsu. Both locations are in northern Kyushu, but they are not the same city.

The discrepancy may arise from differences between the actual cable landing site, the cable station, the nearest major telecommunications hub, the administrative name of the area, and the point used by mapping databases. For precise technical descriptions, Kitakyushu and Fukutsu should not be automatically considered interchangeable: Kitakyushu is marked on system maps, but Fukutsu appears in historical project records.

The Role of Guam

Guam is situated roughly between East Asia, Australia, and the central Pacific. This strategic location has made the island one of the largest regional cable hubs. GOKI lands at Tumon Bay, one of Guam's cable landing areas. Numerous systems pass through the island, connecting Japan, Australia, Southeast Asia, Hawaii, and the continental United States.

For AT&T, the Guam-Japan route could serve multiple purposes: handling its international traffic, providing redundancy for other trans-Pacific routes, connecting AT&T's infrastructure in Guam and Japan, transmitting corporate and carrier data, selling or leasing capacity to partners, and creating an additional pathway to other systems converging on Guam.

It cannot be definitively stated that GOKI carries any specific type of government or military traffic. While Guam does hold strategic importance for the U.S., this does not imply that the cable is predominantly used by military organizations.

Latency Physics: Why Two Different Limits Are Reported

The full length of GOKI is approximately 4,244 km. If a signal traverses this entire length, the idealized physical minimum latency would be approximately 20.8 ms one-way and 41.6 ms round-trip (assuming light speed in fiber is around 204,000 km/s).

However, GeoCables lists a physical limit of 26.0 ms and the best RTT as 50.4 ms with a ratio of 1.94x. This is not a calculation error or contradiction: the reported figure intentionally refers to a specific segment. From the 26 ms value, the estimated length of this segment can be derived: 26 ms x 204,000 km/s / 2 = approximately 2,650 km. This corresponds to the Kitakyushu-Tumon Bay segment, between two specific landing points where measurements are conducted.

Thus, the system has two distinct figures, and they should not be confused:

• 41.6 ms - the approximate limit for the full published length of GOKI (4,244 km), which is not being measured;
• 26.0 ms - the calculated limit for the specific measured segment Kitakyushu-Tumon Bay (approximately 2,650 km);
• 50.4 ms - the minimum observed RTT for this segment, yielding a ratio of 1.94x specifically to the segment's limit.

Comparing the observed 50.4 ms to the full system limit of 41.6 ms and calling the ratio 1.94x would be mathematically incorrect. For multi-point systems where the cable branches across multiple territories, a single meaningful "ratio to the limit" does not exist: measurements are only comparable to the segment on which they are conducted. Therefore, GOKI's ratio is specified for the Kitakyushu-Tumon Bay segment, alongside its length.

What 30-Day Measurements Show

For the Kitakyushu-Tumon Bay direction, the following metrics were recorded: 72 measurements, minimum RTT of 50.4 ms, average RTT of 139.5 ms, maximum RTT of 150.5 ms, standard deviation of 27.25 ms, and a median hop count of 13.

The minimum RTT of 50.4 ms appears physically realistic: it is approximately 1.94 times the calculated limit for the specific segment. However, the average RTT of 139.5 ms requires further explanation. It is nearly three times higher than the minimum RTT, with a maximum of 150.5 ms. This suggests the presence of two distinct routing modes: a small portion of measurements followed a short route with RTT around 50 ms, while the majority took a longer detour with RTT between 140-150 ms.

This distribution may result from changes in BGP routing, use of another submarine cable, detours through Tokyo, Singapore, Hong Kong, or the U.S., changes in the destination address, responses from anycast infrastructure, or switches between carrier networks.

The main takeaway: the average RTT of 139.5 ms does not reflect GOKI's physical performance. It reflects a mix of complete IP routes, some of which may not pass through this cable at all. The two stable latency levels-around 50 ms and 145 ms-indicate route switching rather than gradual load increases on the line.

Why Measurements from Singapore and Sydney Look Odd

Older minimum values from Singapore and Sydney-66 ms and 71 ms-could theoretically correspond to relatively direct regional routes to Guam. However, in the current 30-day sample, the metrics are significantly higher: Singapore-Tumon Bay minimum RTT is 201.1 ms with an average of 281.2 ms; Sydney-Tumon Bay minimum RTT is 246.8 ms with an average of 250.5 ms. These are very high values for regions geographically close to Guam.

The most likely explanation is that traffic is not following the shortest oceanic route. For example, the route may first go to another Asian hub, the U.S., or a major external network before returning to Guam. This is a good example of why geographic proximity and the presence of a cable do not guarantee low latency. The internet selects routes based on commercial agreements, BGP policies, peering availability, transit costs, current network conditions, and the addressing of the destination node.

Remote Probes Do Not Measure GOKI

Latencies from Kyiv, Minsk, Moscow, Tbilisi, Jerusalem, Cape Town, or Almaty pertain to the full international path to the Tumon Bay destination: Kyiv around 273-277 ms, Moscow around 285-290 ms, Jerusalem around 308-314 ms, Cape Town up to 493 ms, Almaty around 336-370 ms.

These figures are useful for assessing the global accessibility of the Guam node but reveal little about GOKI's performance. Without traceroute data, it is impossible to determine whether traffic passed through Japan, utilized GOKI, routed through the U.S., which submarine system was used, or where the latency occurred. Therefore, it is incorrect to claim that GOKI has an RTT of 300 ms based on measurements from Jerusalem or Moscow.

Known Incidents and Failures

No reliably confirmed history of major physical damage to GOKI has been found in publicly available sources. This does not mean the cable has never been repaired or experienced brief outages: private operators are not obligated to publicly report every incident, especially if traffic is quickly rerouted to backup infrastructure.

At the time of available monitoring, GOKI is listed as operational, and no confirmed anomalies have been recorded in our sample. Therefore, the correct conclusion is: no publicly confirmed major incidents involving GOKI have been found in available sources, and observed RTT changes may be related to IP routing and are not evidence of physical cable damage.

What Are the Most Significant Risks?

GOKI's route traverses the seismically active western Pacific Ocean. Japan, Okinawa, and Guam are located in a region prone to earthquakes, typhoons, submarine landslides, and volcanic activity.

Submarine earthquakes. A strong earthquake can cause ground displacement or submarine landslides. The greatest danger comes not from the tremor itself but from the movement of large masses of seabed sediment, which can sever multiple cables simultaneously.

Typhoons. At great depths, the cable is usually protected from waves. However, typhoons can damage shore stations, power supplies, terrestrial lines, and shallow-water segments.

Anchors and fishing. Most cable damage occurs near the shore. In the deep-sea portion, GOKI is relatively protected, but approaches to Tumon Bay, Naha, and Kyushu are vulnerable to human activity.

Infrastructure aging. The reuse of TPC-5 components makes the system's age a particularly interesting question. When evaluating its lifespan, one must consider not only GOKI's formal RFS but also the age of individual reused submarine elements. This does not mean that an older cable is automatically unreliable: segments undergo inspection before re-laying. However, the remaining lifespan and availability of compatible components may affect future operations.

Real Redundancy

Neighboring systems such as KJCN, JIH, MOC, YUI, and AJC are often cited as GOKI's backup. This is an oversimplification. While these systems do provide alternative connectivity in Japan, Okinawa, and Guam, they are not necessarily automatic backups.

KJCN connects Japan to South Korea but does not replace the direct route to Guam. Domestic Japanese cables help route traffic from Okinawa to the main islands but do not provide an international path to Guam. AJC, which passes through Guam and Japan, is a closer functional alternative. Other Guam-based systems can route traffic through Australia, the U.S., or other Asian hubs, but with higher latency.

For effective redundancy, an operator needs capacity rights in an alternative system, configured routing, available bandwidth, independent shore infrastructure, independent terrestrial backhaul, and routes that do not pass through the same damaged area. Thus, while the abundance of cables around Guam and Japan enhances the region's overall resilience, it does not guarantee seamless replacement for GOKI.

Conclusion

• GOKI is an AT&T cable approximately 4,244 km long, connecting Tumon Bay in Guam, Naha in Okinawa, and northern Kyushu. Despite its name, no confirmed landing exists in Incheon.
• The system was created by repurposing resources from the decommissioned TPC-5; optical equipment was supplied by Xtera Communications, and marine operations were conducted by Kokusai Cable Ship.
• The initial known configuration consisted of eight channels of 10 Gbps, providing approximately 80 Gbps of equipped capacity. The number of fiber pairs and current capacity after potential upgrades remain publicly unconfirmed.
• There is a genuine discrepancy in the commissioning date: modern catalogs list 2013, while historical records suggest 2017.
• A minimum RTT of 50.4 ms between Kitakyushu and Tumon Bay is physically plausible. The limit of 26 ms applies to this specific segment (approximately 2,650 km), not the entire system length; the limit for the full length is approximately 41.6 ms.
• The average RTT of 139.5 ms indicates changes in IP routing or the use of alternative infrastructure, rather than typical cable latency.
• No publicly confirmed major incidents involving GOKI have been found, so claims of damage without operator confirmation should be considered unverified.
• The historical significance of GOKI lies in its demonstration that submarine infrastructure does not always end its life with the original project-older oceanic segments can be recovered, retrofitted, and transformed into new operational systems.