Ulleung-Mainland 2 cable: endpoint unreachable from all probes, 26 Sep 2026
What we measured
| Cable | Ulleung-Mainland 2 |
| Segment | Kazakhstan → Ulleung |
| Detected | 2026-09-26 09:01 UTC |
| Resolved | 2026-09-26 21:02 UTC |
| Duration | 12h 0m |
| Observed latency | 310.7 ms |
| Severity | critical |
Who is affected
Countries where Ulleung-Mainland 2 comes ashore, how much of their submarine diversity this cable represents, and what our measurements into them show.
| Country | Dependence on this cable | Other submarine cables | What the measurements show |
|---|---|---|---|
| South Korea resilience index: 100 · resilient |
1 of 17 cables (6% of submarine diversity) | APCN-2, Asia Pacific Gateway (APG), Asia United Gateway East (AUG East) +13 more | no measurement today; median 110 ms over 30 days (34 routes) |
Dependence is structural (share of the country's submarine cables), not a traffic share: real traffic distribution across cables is not public.
Vessels nearby at the time of the incident
No vessel activity was seen within 5 km of the cable route in the window from 48 hours before to 6 hours after the start (by AIS; vessels with transmitters off are not visible).
Path analysis
Traffic changed route while latency was elevated. A reroute of this kind usually follows a fault somewhere on the original path.
Cross-probe verdict. Too few independent vantage points were watching this endpoint to reach a cross-probe verdict.
Timeline
- Alert #207 improving: 1/3 consecutive OK
- Alert #207 improving: 2/3 consecutive OK
- Alert #207 resolved: RTT 310.7ms (baseline 0ms), 4 consecutive OK
Evidence
Network measurements behind this detection, verifiable independently:
Detection method
Latency is sampled continuously from our probe network. An alert opens when round-trip time to a monitored endpoint holds above its rolling baseline, and closes automatically once it returns. Full method is described on the methodology page.