STO-HEL-One: A Sweden-Finland Submarine Cable
The STO-HEL-One submarine cable connects Sweden and Finland across the Baltic Sea, providing telecommunications infrastructure between the two countries. Owned by GlobalConnect, the cable has been operational since 2008, according to GeoCables records. It spans approximately 560 kilometers and lands at four points:
Nothamnsbacken in Sweden, and
Hamnäs,
Lokalahti, and
Skatörarna in Finland.
While STO-HEL-One is listed as in service, several technical details about its design and capacity remain undisclosed in public sources. These include its design capacity, the number of fiber pairs, the supplier, and specific technological specifications. Such gaps in publicly available data make it challenging to fully assess the cable's operational characteristics and potential.
Quick facts
| Name |
STO-HEL-One |
| Length |
560 km |
| Ready for Service (RFS) |
2008 (GeoCables database) |
| Owner |
GlobalConnect |
| Status |
In service |
| Design Capacity |
Not disclosed |
| Fiber Pairs |
Not disclosed |
| Supplier |
Not disclosed |
| Technology |
Not disclosed |
| Landing Points |
Hamnäs (Finland), Lokalahti (Finland), Nothamnsbacken (Sweden), Skatörarna (Finland) |
Route
The STO-HEL-One cable connects Sweden and Finland via the Baltic Sea, landing at Nothamnsbacken in Sweden and three locations in Finland: Hamnäs, Lokalahti, and Skatörarna. This routing provides direct connectivity between the two countries, bypassing terrestrial routes and reducing latency for cross-border data transmission.
Lokalahti is also a landing site for another submarine cable,
Mjolner West, which suggests that the area is a hub for international connectivity in Finland. The cable's Swedish landing point, Nothamnsbacken, is strategically positioned to link Sweden's telecommunications network to Finland's.
Why it was built and what it carries
STO-HEL-One was likely constructed to enhance connectivity between Sweden and Finland, two countries with strong economic and cultural ties. Submarine cables like this one are essential for supporting international data traffic, including internet, voice, and enterprise communications. While the specific data capacity of STO-HEL-One is not disclosed, its role in facilitating cross-border connectivity is evident.
The Baltic Sea corridor is a critical region for telecommunications infrastructure due to its proximity to multiple Nordic and Baltic countries. STO-HEL-One contributes to the redundancy and resilience of the region's network, ensuring reliable communication between Sweden and Finland.
History: what can be established
According to GeoCables records, STO-HEL-One became ready for service in 2008. No alternative dates are mentioned in industry sources, so this year is assumed to be accurate. The cable has been listed as in service since its deployment, and its ownership by GlobalConnect suggests it is part of a broader network strategy in the Nordic region.
Publicly available information does not provide insights into the construction timeline, initial testing, or specific milestones during its operational history. This lack of detail highlights the limited transparency surrounding some submarine cable projects.
Capacity and technology
The design capacity, number of fiber pairs, supplier, and technology used in STO-HEL-One are not disclosed in publicly available sources. Without operator documentation, it is impossible to provide a definitive assessment of the cable's technical specifications. However, it is reasonable to assume that the cable employs industry-standard optical fiber technology to achieve high-speed data transmission across the Baltic Sea.
Latency: the physics
The computed one-way light propagation latency for STO-HEL-One over its 560 km length is approximately 2.7 milliseconds, with a theoretical round-trip time (RTT) floor of 5.5 milliseconds. This calculation assumes light travels through fiber at speeds between 200,000 and 204,000 km/s.
Live measurements conducted via remote probes show significantly higher RTT values, as expected due to the inclusion of land tails, terminal equipment, and routing. For example:
- Nothamnsbacken to Lokalahti: Minimum 10.4 ms, average 14.2 ms over 77 checks.
- Saint Petersburg to Lokalahti: Minimum 21.1 ms, average 21.5 ms over 8 checks.
- Minsk to Lokalahti: Minimum 52.1 ms, average 52.2 ms over 8 checks.
Anomalous measurements, such as a reported minimum of 0.9 ms for Lokalahti to Nothamnsbacken, are below the physical latency floor and should be treated as artifacts caused by rate-limited ICMP replies or other measurement inaccuracies. These values do not reflect the actual performance of the cable.
Redundancy: what happens if it breaks
In the event of a failure, redundancy in the Baltic Sea corridor is supported by alternative cables, such as Mjolner West, which also lands at Lokalahti. This redundancy ensures that connectivity between Sweden and Finland can be maintained through other routes. Repairs to submarine cables typically involve specialized vessels equipped to locate, retrieve, and fix the damaged sections. However, repair times can vary depending on weather conditions, the nature of the fault, and the availability of repair ships.
Bottom line
- STO-HEL-One is a submarine cable connecting Sweden and Finland, operational since 2008.
- Owned by GlobalConnect, it spans 560 km and lands at four points: Nothamnsbacken (Sweden), Hamnäs, Lokalahti, and Skatörarna (Finland).
- Technical specifications such as design capacity, fiber pairs, supplier, and technology are not publicly disclosed.
- Computed latency floor is approximately 5.5 ms RTT over the wet segment; real-world measurements show higher values due to additional network factors.
- Redundancy is supported by other cables in the Baltic Sea corridor, such as Mjolner West.