Sirius South: A Submarine Cable Linking Blackpool and Dublin
Sirius South is a submarine telecommunications cable connecting Blackpool in the United Kingdom to Dublin in Ireland. With a length of 219 kilometers, it is owned and operated by Virgin Media Business and is listed as in service. This cable serves as one of several critical links between the UK and Ireland, supporting data transmission across the Irish Sea.
While Sirius South has been recorded as ready for service (RFS) since 1999 in the GeoCables database, there is limited publicly available information about its design capacity, fiber pair count, supplier, and specific technological features. This lack of transparency makes it challenging to fully assess its technical specifications and operational capabilities.
Quick facts
| Cable name | Sirius South |
| Length | 219 km |
| Ready for service | 1999 (GeoCables database; conflicting industry sources, if any, not identified) |
| Owners | Virgin Media Business |
| Status | In service |
| Design capacity | Not disclosed |
| Fiber pairs | Not disclosed |
| Supplier | Not disclosed |
| Technology | Not disclosed |
| Landing points | Blackpool (United Kingdom), Dublin (Ireland) |
Route
Sirius South spans the Irish Sea, connecting Blackpool on the northwestern coast of England to Dublin, Ireland's capital city. Blackpool is a hub for multiple submarine cables, including
E-LLAN,
Havhingsten/CeltixConnect-2 (CC-2), and
Lanis-1. Similarly, Dublin serves as a major landing point for several other cables, such as
CeltixConnect-1 (CC-1), EXA North, and EXA South. This geographic proximity to other cables provides redundancy options for data traffic between the UK and Ireland.
Why it was built and what it carries
Sirius South was built to enhance connectivity between the United Kingdom and Ireland, two countries with significant economic, cultural, and technological ties. The cable likely supports a mix of commercial internet traffic, enterprise data, and potentially wholesale bandwidth services. Its role in the broader telecom infrastructure is to facilitate high-speed, reliable connectivity across the Irish Sea, contributing to the smooth exchange of data between the two nations.
History: what can be established
The GeoCables database lists Sirius South as ready for service since 1999. Publicly available information does not indicate any conflicting dates from industry sources, nor does it provide details about the construction process, initial capacity, or subsequent upgrades. The lack of transparency in its historical documentation leaves room for uncertainty about its development and operational milestones.
Capacity and technology
The design capacity and fiber pair count of Sirius South are not disclosed in public sources. Similarly, information about the supplier and specific technological features, such as modulation formats or repeater configurations, is unavailable. Without operator documentation or industry confirmation, attributing technical specifications to this cable would be speculative.
Latency: the physics
The theoretical one-way light propagation latency over Sirius South's 219 km wet segment is approximately 1.1 milliseconds, with a round-trip time (RTT) floor of 2.1 milliseconds. However, real-world end-to-end latency is higher due to additional factors such as land-based tails, terminal equipment delays, and routing inefficiencies.
Remote probes measuring the full internet path between Blackpool and Dublin reported a minimum RTT of 2.1 milliseconds and an average of 48.7 milliseconds over 243 checks. The minimum value of 2.1 milliseconds matches the theoretical floor but is flagged as a measurement artifact, likely caused by rate-limited ICMP replies from intermediate routers. This artifact should not be interpreted as the actual cable performance. For the reverse direction, Dublin to Blackpool, the minimum RTT was recorded as 22.2 milliseconds, with an average of 52.0 milliseconds over 30 checks. These values reflect the broader internet path rather than the cable's isolated latency.
Redundancy: what happens if it breaks
In the event of a disruption to Sirius South, several alternative cables are available to maintain connectivity between the UK and Ireland. At Blackpool, redundancy options include E-LLAN, Havhingsten/CeltixConnect-2 (CC-2), and Lanis-1. Dublin offers additional alternatives such as CeltixConnect-1 (CC-1), EXA North, and EXA South. Standard industry practices for submarine cable repair, including fault localization, cable retrieval, and splicing, would be employed to restore service. However, repair timelines can vary depending on weather conditions, cable burial depth, and the availability of specialized vessels.
Bottom line
- Sirius South is a 219 km submarine cable connecting Blackpool, UK, to Dublin, Ireland.
- Owned by Virgin Media Business, it has been listed as in service since 1999.
- Design capacity, fiber pair count, supplier, and technological details are not publicly disclosed.
- Theoretical RTT floor over the wet segment is approximately 2.1 ms, but real-world latency is higher due to additional factors.
- Redundancy is available via other cables landing at Blackpool and Dublin.