Sirius North: A Short Submarine Cable in the United Kingdom
Sirius North is a submarine telecommunications cable connecting
Carrickfergus in Northern Ireland to
Saltcoats in Scotland, United Kingdom. Spanning a modest 147 kilometers, it is owned and operated by Virgin Media Business and has been listed as in service since its recorded ready-for-service (RFS) year of 1999. Its primary purpose is to facilitate regional connectivity across the Irish Sea.
What makes Sirius North particularly interesting is the scarcity of publicly disclosed technical details about its design and capacity. While its short length suggests it is a regional cable rather than a transcontinental one, the absence of information on fiber pairs, supplier, and technology leaves its exact specifications open to speculation. This lack of transparency is not uncommon for older cables, particularly those serving domestic markets.
Quick facts
| Length | 147 km |
| Ready-for-Service (RFS) Year | 1999 (GeoCables database value; no conflicting sources surfaced) |
| Owners | Virgin Media Business |
| Status | In service |
| Design Capacity | Not disclosed |
| Fiber Pairs | Not disclosed |
| Supplier | Not disclosed |
| Technology | Not disclosed |
| Landing Points | Carrickfergus (United Kingdom); Saltcoats (United Kingdom) |
| One-way Latency (theoretical) | 0.7 ms |
| Round-trip Latency (theoretical floor) | 1.4 ms |
Route
Sirius North connects Carrickfergus, a town on the northern coast of Northern Ireland, to Saltcoats, a town on the western coast of Scotland. This route spans the North Channel, a narrow portion of the Irish Sea. The cable's corridor is geographically straightforward, avoiding the complexities of deep ocean trenches or multiple branching units that characterize longer international cables.
Carrickfergus is historically significant as one of Northern Ireland's oldest towns, while Saltcoats is a small coastal town in North Ayrshire. Both locations are well-suited for cable landings due to their proximity to stable infrastructure and manageable coastal conditions.
Why it was built and what it carries
Sirius North was likely built to enhance regional connectivity between Northern Ireland and Scotland, providing a dedicated link for telecommunications traffic. It serves as part of Virgin Media Business's network infrastructure, supporting enterprise communications, broadband services, and potentially other data traffic. Its relatively short length and domestic scope suggest it is not designed for high-capacity international transit but rather for reliable regional service.
History: what can be established
The GeoCables database lists Sirius North's ready-for-service year as 1999, and no conflicting industry sources have surfaced to challenge this date. This places the cable among the older submarine systems still in operation, which is notable given the rapid technological advancements in the industry since the late 1990s.
While details about its construction, supplier, and initial deployment are not publicly disclosed, its continued service suggests it has been adequately maintained or upgraded to meet evolving demands. Virgin Media Business's role as the operator aligns with its focus on UK-based connectivity solutions.
Capacity and technology
Publicly available data does not disclose the design capacity, fiber pair count, supplier, or specific technology used in Sirius North. Without operator documentation or reliable sources, attributing these specifications would be speculative. Given its age, it is reasonable to assume that its original capacity was modest compared to modern systems, but potential upgrades over time cannot be ruled out.
Latency: the physics
The theoretical one-way latency for light propagation over the 147 km wet segment of Sirius North is approximately 0.7 milliseconds, with a round-trip time (RTT) floor of 1.4 milliseconds. These calculations assume light travels through fiber at speeds between 200,000 and 204,000 km/s. However, real-world end-to-end latency is higher due to factors such as land-based network tails, terminal equipment processing, and routing inefficiencies. No live measurements of latency are currently available for this cable.
Redundancy: what happens if it breaks
In the event of a failure, redundancy for Sirius North would depend on alternative routes across the Irish Sea. Other cables or terrestrial networks connecting Northern Ireland and Scotland could potentially reroute traffic, though specific alternatives are not listed in the GeoCables database. Repair logistics for a cable of this length are relatively straightforward compared to deep-sea systems, with cable ships typically able to access the North Channel's shallow waters without significant difficulty.
Bottom line
- Sirius North is a 147 km submarine cable connecting Carrickfergus and Saltcoats in the United Kingdom.
- Owned by Virgin Media Business, it has been listed as in service since 1999.
- Publicly disclosed technical details, including design capacity, fiber pairs, supplier, and technology, are not available.
- Theoretical latency over the wet segment is 0.7 ms one-way, with a round-trip floor of 1.4 ms.
- Redundancy would rely on alternative Irish Sea routes, though specifics are not documented.