Groix 4: Short-distance submarine cable connecting mainland France to Groix Island
The Groix 4 submarine cable is a 7-kilometer fiber optic system connecting
Petit Perello on the French mainland to
Port Nâl on Groix Island, located off the coast of Brittany, France. Owned by Orange, a major telecommunications operator in France, the cable is listed as in service and was recorded as ready for service (RFS) in 2022 in the GeoCables database.
What makes Groix 4 notable is its extremely short length compared to typical submarine cables, which often span hundreds or thousands of kilometers. This cable serves a localized purpose, linking Groix Island to the mainland for telecommunications services. However, public information about its design capacity, fiber pairs, supplier, and technology is not disclosed, leaving certain technical aspects of the cable unknown.
Quick facts
| Cable name | Groix 4 |
| Length (km) | 7 |
| Ready for service (RFS) | 2022 (GeoCables database) |
| Owners | Orange |
| Status | In service |
| Design capacity (Tbps) | Not disclosed |
| Fiber pairs | Not disclosed |
| Supplier | Not disclosed |
| Technology | Not disclosed |
| Landing points | Petit Perello (France); Port Nâl (France) |
Route
Groix 4 spans a short distance across the Bay of Biscay, connecting Petit Perello on the French mainland to Port Nâl on Groix Island. Groix Island is situated approximately 7 kilometers off the coast of Brittany and is known for its scenic landscapes and small population. The cable provides a direct link between the island and mainland France, facilitating telecommunications services for residents and businesses on Groix.
Why it was built and what it carries
The primary purpose of Groix 4 is to ensure reliable connectivity between Groix Island and the mainland. As an island community, Groix relies on submarine cables for internet, phone, and data services, which are essential for modern communication and economic activity. Given the short distance of the cable, it is likely designed to handle relatively modest traffic compared to larger international systems. However, without public disclosure of its design capacity or fiber pairs, the specific capabilities of Groix 4 remain unclear.
History: what can be established
Groix 4 is recorded in the GeoCables database as having been ready for service in 2022. No conflicting dates from industry sources are currently known, so this date is treated as accurate. The cable was built to replace or supplement earlier systems serving Groix Island, ensuring continued connectivity for the local population. Details about its construction, including the supplier and installation process, are not publicly documented.
Capacity and technology
The design capacity of Groix 4, as well as the number of fiber pairs it contains, has not been disclosed in public sources. Similarly, no information is available regarding the specific technology used in the cable, such as whether it employs wavelength division multiplexing (WDM) or other advanced techniques. Without operator documentation, attributing these details would be speculative.
Latency: the physics
Theoretical latency for Groix 4 is extremely low due to its short length. Light propagation over the 7-kilometer wet segment results in a one-way latency of approximately 0.0 milliseconds, with a round-trip time (RTT) floor of about 0.1 milliseconds when accounting for the speed of light in fiber (200-204,000 km/s). However, real-world latency will be higher due to factors such as land-based tails, terminal equipment, and routing. No live measurements are currently available for this cable.
Redundancy: what happens if it breaks
If Groix 4 were to experience a fault, redundancy would depend on alternative systems serving Groix Island. While specific details about backup cables or microwave links are not provided in the GeoCables database, island communities often rely on secondary systems to ensure continuity of service during outages. Repairs on short cables like Groix 4 are typically faster than on longer systems, as the localized nature of the route simplifies logistics. Standard industry practices for submarine cable repair include deploying specialized ships to locate and fix faults, often by replacing damaged sections of the cable.
Bottom line
- Groix 4 is a 7-kilometer submarine cable connecting Petit Perello to Port Nâl on Groix Island.
- Owned by Orange, it was recorded as ready for service in 2022.
- Design capacity, fiber pairs, supplier, and technology are not publicly disclosed.
- Theoretical latency is minimal due to the cable's short length, but real-world latency is higher.
- Redundancy and repair logistics are likely straightforward given the localized nature of the cable.